LCOV - code coverage report
Current view: top level - contrib/postgres_fdw - connection.c (source / functions) Hit Total Coverage
Test: PostgreSQL 11devel Lines: 260 333 78.1 %
Date: 2018-05-21 18:20:01 Functions: 19 20 95.0 %
Legend: Lines: hit not hit

          Line data    Source code
       1             : /*-------------------------------------------------------------------------
       2             :  *
       3             :  * connection.c
       4             :  *        Connection management functions for postgres_fdw
       5             :  *
       6             :  * Portions Copyright (c) 2012-2018, PostgreSQL Global Development Group
       7             :  *
       8             :  * IDENTIFICATION
       9             :  *        contrib/postgres_fdw/connection.c
      10             :  *
      11             :  *-------------------------------------------------------------------------
      12             :  */
      13             : #include "postgres.h"
      14             : 
      15             : #include "postgres_fdw.h"
      16             : 
      17             : #include "access/htup_details.h"
      18             : #include "catalog/pg_user_mapping.h"
      19             : #include "access/xact.h"
      20             : #include "mb/pg_wchar.h"
      21             : #include "miscadmin.h"
      22             : #include "pgstat.h"
      23             : #include "storage/latch.h"
      24             : #include "utils/hsearch.h"
      25             : #include "utils/inval.h"
      26             : #include "utils/memutils.h"
      27             : #include "utils/syscache.h"
      28             : 
      29             : 
      30             : /*
      31             :  * Connection cache hash table entry
      32             :  *
      33             :  * The lookup key in this hash table is the user mapping OID. We use just one
      34             :  * connection per user mapping ID, which ensures that all the scans use the
      35             :  * same snapshot during a query.  Using the user mapping OID rather than
      36             :  * the foreign server OID + user OID avoids creating multiple connections when
      37             :  * the public user mapping applies to all user OIDs.
      38             :  *
      39             :  * The "conn" pointer can be NULL if we don't currently have a live connection.
      40             :  * When we do have a connection, xact_depth tracks the current depth of
      41             :  * transactions and subtransactions open on the remote side.  We need to issue
      42             :  * commands at the same nesting depth on the remote as we're executing at
      43             :  * ourselves, so that rolling back a subtransaction will kill the right
      44             :  * queries and not the wrong ones.
      45             :  */
      46             : typedef Oid ConnCacheKey;
      47             : 
      48             : typedef struct ConnCacheEntry
      49             : {
      50             :     ConnCacheKey key;           /* hash key (must be first) */
      51             :     PGconn     *conn;           /* connection to foreign server, or NULL */
      52             :     /* Remaining fields are invalid when conn is NULL: */
      53             :     int         xact_depth;     /* 0 = no xact open, 1 = main xact open, 2 =
      54             :                                  * one level of subxact open, etc */
      55             :     bool        have_prep_stmt; /* have we prepared any stmts in this xact? */
      56             :     bool        have_error;     /* have any subxacts aborted in this xact? */
      57             :     bool        changing_xact_state;    /* xact state change in process */
      58             :     bool        invalidated;    /* true if reconnect is pending */
      59             :     uint32      server_hashvalue;   /* hash value of foreign server OID */
      60             :     uint32      mapping_hashvalue;  /* hash value of user mapping OID */
      61             : } ConnCacheEntry;
      62             : 
      63             : /*
      64             :  * Connection cache (initialized on first use)
      65             :  */
      66             : static HTAB *ConnectionHash = NULL;
      67             : 
      68             : /* for assigning cursor numbers and prepared statement numbers */
      69             : static unsigned int cursor_number = 0;
      70             : static unsigned int prep_stmt_number = 0;
      71             : 
      72             : /* tracks whether any work is needed in callback functions */
      73             : static bool xact_got_connection = false;
      74             : 
      75             : /* prototypes of private functions */
      76             : static PGconn *connect_pg_server(ForeignServer *server, UserMapping *user);
      77             : static void disconnect_pg_server(ConnCacheEntry *entry);
      78             : static void check_conn_params(const char **keywords, const char **values, UserMapping *user);
      79             : static void configure_remote_session(PGconn *conn);
      80             : static void do_sql_command(PGconn *conn, const char *sql);
      81             : static void begin_remote_xact(ConnCacheEntry *entry);
      82             : static void pgfdw_xact_callback(XactEvent event, void *arg);
      83             : static void pgfdw_subxact_callback(SubXactEvent event,
      84             :                        SubTransactionId mySubid,
      85             :                        SubTransactionId parentSubid,
      86             :                        void *arg);
      87             : static void pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue);
      88             : static void pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry);
      89             : static bool pgfdw_cancel_query(PGconn *conn);
      90             : static bool pgfdw_exec_cleanup_query(PGconn *conn, const char *query,
      91             :                          bool ignore_errors);
      92             : static bool pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime,
      93             :                          PGresult **result);
      94             : 
      95             : 
      96             : /*
      97             :  * Get a PGconn which can be used to execute queries on the remote PostgreSQL
      98             :  * server with the user's authorization.  A new connection is established
      99             :  * if we don't already have a suitable one, and a transaction is opened at
     100             :  * the right subtransaction nesting depth if we didn't do that already.
     101             :  *
     102             :  * will_prep_stmt must be true if caller intends to create any prepared
     103             :  * statements.  Since those don't go away automatically at transaction end
     104             :  * (not even on error), we need this flag to cue manual cleanup.
     105             :  */
     106             : PGconn *
     107        2626 : GetConnection(UserMapping *user, bool will_prep_stmt)
     108             : {
     109             :     bool        found;
     110             :     ConnCacheEntry *entry;
     111             :     ConnCacheKey key;
     112             : 
     113             :     /* First time through, initialize connection cache hashtable */
     114        2626 :     if (ConnectionHash == NULL)
     115             :     {
     116             :         HASHCTL     ctl;
     117             : 
     118           2 :         MemSet(&ctl, 0, sizeof(ctl));
     119           2 :         ctl.keysize = sizeof(ConnCacheKey);
     120           2 :         ctl.entrysize = sizeof(ConnCacheEntry);
     121             :         /* allocate ConnectionHash in the cache context */
     122           2 :         ctl.hcxt = CacheMemoryContext;
     123           2 :         ConnectionHash = hash_create("postgres_fdw connections", 8,
     124             :                                      &ctl,
     125             :                                      HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
     126             : 
     127             :         /*
     128             :          * Register some callback functions that manage connection cleanup.
     129             :          * This should be done just once in each backend.
     130             :          */
     131           2 :         RegisterXactCallback(pgfdw_xact_callback, NULL);
     132           2 :         RegisterSubXactCallback(pgfdw_subxact_callback, NULL);
     133           2 :         CacheRegisterSyscacheCallback(FOREIGNSERVEROID,
     134             :                                       pgfdw_inval_callback, (Datum) 0);
     135           2 :         CacheRegisterSyscacheCallback(USERMAPPINGOID,
     136             :                                       pgfdw_inval_callback, (Datum) 0);
     137             :     }
     138             : 
     139             :     /* Set flag that we did GetConnection during the current transaction */
     140        2626 :     xact_got_connection = true;
     141             : 
     142             :     /* Create hash key for the entry.  Assume no pad bytes in key struct */
     143        2626 :     key = user->umid;
     144             : 
     145             :     /*
     146             :      * Find or create cached entry for requested connection.
     147             :      */
     148        2626 :     entry = hash_search(ConnectionHash, &key, HASH_ENTER, &found);
     149        2626 :     if (!found)
     150             :     {
     151             :         /*
     152             :          * We need only clear "conn" here; remaining fields will be filled
     153             :          * later when "conn" is set.
     154             :          */
     155           6 :         entry->conn = NULL;
     156             :     }
     157             : 
     158             :     /* Reject further use of connections which failed abort cleanup. */
     159        2626 :     pgfdw_reject_incomplete_xact_state_change(entry);
     160             : 
     161             :     /*
     162             :      * If the connection needs to be remade due to invalidation, disconnect as
     163             :      * soon as we're out of all transactions.
     164             :      */
     165        2626 :     if (entry->conn != NULL && entry->invalidated && entry->xact_depth == 0)
     166             :     {
     167          26 :         elog(DEBUG3, "closing connection %p for option changes to take effect",
     168             :              entry->conn);
     169          26 :         disconnect_pg_server(entry);
     170             :     }
     171             : 
     172             :     /*
     173             :      * We don't check the health of cached connection here, because it would
     174             :      * require some overhead.  Broken connection will be detected when the
     175             :      * connection is actually used.
     176             :      */
     177             : 
     178             :     /*
     179             :      * If cache entry doesn't have a connection, we have to establish a new
     180             :      * connection.  (If connect_pg_server throws an error, the cache entry
     181             :      * will remain in a valid empty state, ie conn == NULL.)
     182             :      */
     183        2626 :     if (entry->conn == NULL)
     184             :     {
     185          36 :         ForeignServer *server = GetForeignServer(user->serverid);
     186             : 
     187             :         /* Reset all transient state fields, to be sure all are clean */
     188          36 :         entry->xact_depth = 0;
     189          36 :         entry->have_prep_stmt = false;
     190          36 :         entry->have_error = false;
     191          36 :         entry->changing_xact_state = false;
     192          36 :         entry->invalidated = false;
     193          36 :         entry->server_hashvalue =
     194          36 :             GetSysCacheHashValue1(FOREIGNSERVEROID,
     195             :                                   ObjectIdGetDatum(server->serverid));
     196          36 :         entry->mapping_hashvalue =
     197          36 :             GetSysCacheHashValue1(USERMAPPINGOID,
     198             :                                   ObjectIdGetDatum(user->umid));
     199             : 
     200             :         /* Now try to make the connection */
     201          36 :         entry->conn = connect_pg_server(server, user);
     202             : 
     203          32 :         elog(DEBUG3, "new postgres_fdw connection %p for server \"%s\" (user mapping oid %u, userid %u)",
     204             :              entry->conn, server->servername, user->umid, user->userid);
     205             :     }
     206             : 
     207             :     /*
     208             :      * Start a new transaction or subtransaction if needed.
     209             :      */
     210        2622 :     begin_remote_xact(entry);
     211             : 
     212             :     /* Remember if caller will prepare statements */
     213        2622 :     entry->have_prep_stmt |= will_prep_stmt;
     214             : 
     215        2622 :     return entry->conn;
     216             : }
     217             : 
     218             : /*
     219             :  * Connect to remote server using specified server and user mapping properties.
     220             :  */
     221             : static PGconn *
     222          36 : connect_pg_server(ForeignServer *server, UserMapping *user)
     223             : {
     224          36 :     PGconn     *volatile conn = NULL;
     225             : 
     226             :     /*
     227             :      * Use PG_TRY block to ensure closing connection on error.
     228             :      */
     229          36 :     PG_TRY();
     230             :     {
     231             :         const char **keywords;
     232             :         const char **values;
     233             :         int         n;
     234             : 
     235             :         /*
     236             :          * Construct connection params from generic options of ForeignServer
     237             :          * and UserMapping.  (Some of them might not be libpq options, in
     238             :          * which case we'll just waste a few array slots.)  Add 3 extra slots
     239             :          * for fallback_application_name, client_encoding, end marker.
     240             :          */
     241          36 :         n = list_length(server->options) + list_length(user->options) + 3;
     242          36 :         keywords = (const char **) palloc(n * sizeof(char *));
     243          36 :         values = (const char **) palloc(n * sizeof(char *));
     244             : 
     245          36 :         n = 0;
     246          72 :         n += ExtractConnectionOptions(server->options,
     247          72 :                                       keywords + n, values + n);
     248          72 :         n += ExtractConnectionOptions(user->options,
     249          72 :                                       keywords + n, values + n);
     250             : 
     251             :         /* Use "postgres_fdw" as fallback_application_name. */
     252          36 :         keywords[n] = "fallback_application_name";
     253          36 :         values[n] = "postgres_fdw";
     254          36 :         n++;
     255             : 
     256             :         /* Set client_encoding so that libpq can convert encoding properly. */
     257          36 :         keywords[n] = "client_encoding";
     258          36 :         values[n] = GetDatabaseEncodingName();
     259          36 :         n++;
     260             : 
     261          36 :         keywords[n] = values[n] = NULL;
     262             : 
     263             :         /* verify connection parameters and make connection */
     264          36 :         check_conn_params(keywords, values, user);
     265             : 
     266          36 :         conn = PQconnectdbParams(keywords, values, false);
     267          36 :         if (!conn || PQstatus(conn) != CONNECTION_OK)
     268           4 :             ereport(ERROR,
     269             :                     (errcode(ERRCODE_SQLCLIENT_UNABLE_TO_ESTABLISH_SQLCONNECTION),
     270             :                      errmsg("could not connect to server \"%s\"",
     271             :                             server->servername),
     272             :                      errdetail_internal("%s", pchomp(PQerrorMessage(conn)))));
     273             : 
     274             :         /*
     275             :          * Check that non-superuser has used password to establish connection;
     276             :          * otherwise, he's piggybacking on the postgres server's user
     277             :          * identity. See also dblink_security_check() in contrib/dblink.
     278             :          */
     279          32 :         if (!superuser_arg(user->userid) && !PQconnectionUsedPassword(conn))
     280           0 :             ereport(ERROR,
     281             :                     (errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
     282             :                      errmsg("password is required"),
     283             :                      errdetail("Non-superuser cannot connect if the server does not request a password."),
     284             :                      errhint("Target server's authentication method must be changed.")));
     285             : 
     286             :         /* Prepare new session for use */
     287          32 :         configure_remote_session(conn);
     288             : 
     289          32 :         pfree(keywords);
     290          32 :         pfree(values);
     291             :     }
     292           4 :     PG_CATCH();
     293             :     {
     294             :         /* Release PGconn data structure if we managed to create one */
     295           4 :         if (conn)
     296           4 :             PQfinish(conn);
     297           4 :         PG_RE_THROW();
     298             :     }
     299          32 :     PG_END_TRY();
     300             : 
     301          32 :     return conn;
     302             : }
     303             : 
     304             : /*
     305             :  * Disconnect any open connection for a connection cache entry.
     306             :  */
     307             : static void
     308          26 : disconnect_pg_server(ConnCacheEntry *entry)
     309             : {
     310          26 :     if (entry->conn != NULL)
     311             :     {
     312          26 :         PQfinish(entry->conn);
     313          26 :         entry->conn = NULL;
     314             :     }
     315          26 : }
     316             : 
     317             : /*
     318             :  * For non-superusers, insist that the connstr specify a password.  This
     319             :  * prevents a password from being picked up from .pgpass, a service file,
     320             :  * the environment, etc.  We don't want the postgres user's passwords
     321             :  * to be accessible to non-superusers.  (See also dblink_connstr_check in
     322             :  * contrib/dblink.)
     323             :  */
     324             : static void
     325          36 : check_conn_params(const char **keywords, const char **values, UserMapping *user)
     326             : {
     327             :     int         i;
     328             : 
     329             :     /* no check required if superuser */
     330          36 :     if (superuser_arg(user->userid))
     331          36 :         return;
     332             : 
     333             :     /* ok if params contain a non-empty password */
     334           0 :     for (i = 0; keywords[i] != NULL; i++)
     335             :     {
     336           0 :         if (strcmp(keywords[i], "password") == 0 && values[i][0] != '\0')
     337           0 :             return;
     338             :     }
     339             : 
     340           0 :     ereport(ERROR,
     341             :             (errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
     342             :              errmsg("password is required"),
     343             :              errdetail("Non-superusers must provide a password in the user mapping.")));
     344             : }
     345             : 
     346             : /*
     347             :  * Issue SET commands to make sure remote session is configured properly.
     348             :  *
     349             :  * We do this just once at connection, assuming nothing will change the
     350             :  * values later.  Since we'll never send volatile function calls to the
     351             :  * remote, there shouldn't be any way to break this assumption from our end.
     352             :  * It's possible to think of ways to break it at the remote end, eg making
     353             :  * a foreign table point to a view that includes a set_config call ---
     354             :  * but once you admit the possibility of a malicious view definition,
     355             :  * there are any number of ways to break things.
     356             :  */
     357             : static void
     358          32 : configure_remote_session(PGconn *conn)
     359             : {
     360          32 :     int         remoteversion = PQserverVersion(conn);
     361             : 
     362             :     /* Force the search path to contain only pg_catalog (see deparse.c) */
     363          32 :     do_sql_command(conn, "SET search_path = pg_catalog");
     364             : 
     365             :     /*
     366             :      * Set remote timezone; this is basically just cosmetic, since all
     367             :      * transmitted and returned timestamptzs should specify a zone explicitly
     368             :      * anyway.  However it makes the regression test outputs more predictable.
     369             :      *
     370             :      * We don't risk setting remote zone equal to ours, since the remote
     371             :      * server might use a different timezone database.  Instead, use UTC
     372             :      * (quoted, because very old servers are picky about case).
     373             :      */
     374          32 :     do_sql_command(conn, "SET timezone = 'UTC'");
     375             : 
     376             :     /*
     377             :      * Set values needed to ensure unambiguous data output from remote.  (This
     378             :      * logic should match what pg_dump does.  See also set_transmission_modes
     379             :      * in postgres_fdw.c.)
     380             :      */
     381          32 :     do_sql_command(conn, "SET datestyle = ISO");
     382          32 :     if (remoteversion >= 80400)
     383          32 :         do_sql_command(conn, "SET intervalstyle = postgres");
     384          32 :     if (remoteversion >= 90000)
     385          32 :         do_sql_command(conn, "SET extra_float_digits = 3");
     386             :     else
     387           0 :         do_sql_command(conn, "SET extra_float_digits = 2");
     388          32 : }
     389             : 
     390             : /*
     391             :  * Convenience subroutine to issue a non-data-returning SQL command to remote
     392             :  */
     393             : static void
     394        1880 : do_sql_command(PGconn *conn, const char *sql)
     395             : {
     396             :     PGresult   *res;
     397             : 
     398        1880 :     if (!PQsendQuery(conn, sql))
     399           0 :         pgfdw_report_error(ERROR, NULL, conn, false, sql);
     400        1880 :     res = pgfdw_get_result(conn, sql);
     401        1880 :     if (PQresultStatus(res) != PGRES_COMMAND_OK)
     402           0 :         pgfdw_report_error(ERROR, res, conn, true, sql);
     403        1880 :     PQclear(res);
     404        1880 : }
     405             : 
     406             : /*
     407             :  * Start remote transaction or subtransaction, if needed.
     408             :  *
     409             :  * Note that we always use at least REPEATABLE READ in the remote session.
     410             :  * This is so that, if a query initiates multiple scans of the same or
     411             :  * different foreign tables, we will get snapshot-consistent results from
     412             :  * those scans.  A disadvantage is that we can't provide sane emulation of
     413             :  * READ COMMITTED behavior --- it would be nice if we had some other way to
     414             :  * control which remote queries share a snapshot.
     415             :  */
     416             : static void
     417        2622 : begin_remote_xact(ConnCacheEntry *entry)
     418             : {
     419        2622 :     int         curlevel = GetCurrentTransactionNestLevel();
     420             : 
     421             :     /* Start main transaction if we haven't yet */
     422        2622 :     if (entry->xact_depth <= 0)
     423             :     {
     424             :         const char *sql;
     425             : 
     426         864 :         elog(DEBUG3, "starting remote transaction on connection %p",
     427             :              entry->conn);
     428             : 
     429         864 :         if (IsolationIsSerializable())
     430           0 :             sql = "START TRANSACTION ISOLATION LEVEL SERIALIZABLE";
     431             :         else
     432         864 :             sql = "START TRANSACTION ISOLATION LEVEL REPEATABLE READ";
     433         864 :         entry->changing_xact_state = true;
     434         864 :         do_sql_command(entry->conn, sql);
     435         864 :         entry->xact_depth = 1;
     436         864 :         entry->changing_xact_state = false;
     437             :     }
     438             : 
     439             :     /*
     440             :      * If we're in a subtransaction, stack up savepoints to match our level.
     441             :      * This ensures we can rollback just the desired effects when a
     442             :      * subtransaction aborts.
     443             :      */
     444        5260 :     while (entry->xact_depth < curlevel)
     445             :     {
     446             :         char        sql[64];
     447             : 
     448          16 :         snprintf(sql, sizeof(sql), "SAVEPOINT s%d", entry->xact_depth + 1);
     449          16 :         entry->changing_xact_state = true;
     450          16 :         do_sql_command(entry->conn, sql);
     451          16 :         entry->xact_depth++;
     452          16 :         entry->changing_xact_state = false;
     453             :     }
     454        2622 : }
     455             : 
     456             : /*
     457             :  * Release connection reference count created by calling GetConnection.
     458             :  */
     459             : void
     460        2582 : ReleaseConnection(PGconn *conn)
     461             : {
     462             :     /*
     463             :      * Currently, we don't actually track connection references because all
     464             :      * cleanup is managed on a transaction or subtransaction basis instead. So
     465             :      * there's nothing to do here.
     466             :      */
     467        2582 : }
     468             : 
     469             : /*
     470             :  * Assign a "unique" number for a cursor.
     471             :  *
     472             :  * These really only need to be unique per connection within a transaction.
     473             :  * For the moment we ignore the per-connection point and assign them across
     474             :  * all connections in the transaction, but we ask for the connection to be
     475             :  * supplied in case we want to refine that.
     476             :  *
     477             :  * Note that even if wraparound happens in a very long transaction, actual
     478             :  * collisions are highly improbable; just be sure to use %u not %d to print.
     479             :  */
     480             : unsigned int
     481         620 : GetCursorNumber(PGconn *conn)
     482             : {
     483         620 :     return ++cursor_number;
     484             : }
     485             : 
     486             : /*
     487             :  * Assign a "unique" number for a prepared statement.
     488             :  *
     489             :  * This works much like GetCursorNumber, except that we never reset the counter
     490             :  * within a session.  That's because we can't be 100% sure we've gotten rid
     491             :  * of all prepared statements on all connections, and it's not really worth
     492             :  * increasing the risk of prepared-statement name collisions by resetting.
     493             :  */
     494             : unsigned int
     495         176 : GetPrepStmtNumber(PGconn *conn)
     496             : {
     497         176 :     return ++prep_stmt_number;
     498             : }
     499             : 
     500             : /*
     501             :  * Submit a query and wait for the result.
     502             :  *
     503             :  * This function is interruptible by signals.
     504             :  *
     505             :  * Caller is responsible for the error handling on the result.
     506             :  */
     507             : PGresult *
     508        5820 : pgfdw_exec_query(PGconn *conn, const char *query)
     509             : {
     510             :     /*
     511             :      * Submit a query.  Since we don't use non-blocking mode, this also can
     512             :      * block.  But its risk is relatively small, so we ignore that for now.
     513             :      */
     514        5820 :     if (!PQsendQuery(conn, query))
     515           0 :         pgfdw_report_error(ERROR, NULL, conn, false, query);
     516             : 
     517             :     /* Wait for the result. */
     518        5820 :     return pgfdw_get_result(conn, query);
     519             : }
     520             : 
     521             : /*
     522             :  * Wait for the result from a prior asynchronous execution function call.
     523             :  *
     524             :  * This function offers quick responsiveness by checking for any interruptions.
     525             :  *
     526             :  * This function emulates PQexec()'s behavior of returning the last result
     527             :  * when there are many.
     528             :  *
     529             :  * Caller is responsible for the error handling on the result.
     530             :  */
     531             : PGresult *
     532        9656 : pgfdw_get_result(PGconn *conn, const char *query)
     533             : {
     534        9656 :     PGresult   *volatile last_res = NULL;
     535             : 
     536             :     /* In what follows, do not leak any PGresults on an error. */
     537        9656 :     PG_TRY();
     538             :     {
     539             :         for (;;)
     540        9656 :         {
     541             :             PGresult   *res;
     542             : 
     543       48376 :             while (PQisBusy(conn))
     544             :             {
     545             :                 int         wc;
     546             : 
     547             :                 /* Sleep until there's something to do */
     548        9752 :                 wc = WaitLatchOrSocket(MyLatch,
     549             :                                        WL_LATCH_SET | WL_SOCKET_READABLE,
     550             :                                        PQsocket(conn),
     551             :                                        -1L, PG_WAIT_EXTENSION);
     552        9752 :                 ResetLatch(MyLatch);
     553             : 
     554        9752 :                 CHECK_FOR_INTERRUPTS();
     555             : 
     556             :                 /* Data available in socket? */
     557        9752 :                 if (wc & WL_SOCKET_READABLE)
     558             :                 {
     559        9752 :                     if (!PQconsumeInput(conn))
     560           0 :                         pgfdw_report_error(ERROR, NULL, conn, false, query);
     561             :                 }
     562             :             }
     563             : 
     564       19312 :             res = PQgetResult(conn);
     565       19312 :             if (res == NULL)
     566        9656 :                 break;          /* query is complete */
     567             : 
     568        9656 :             PQclear(last_res);
     569        9656 :             last_res = res;
     570             :         }
     571             :     }
     572           0 :     PG_CATCH();
     573             :     {
     574           0 :         PQclear(last_res);
     575           0 :         PG_RE_THROW();
     576             :     }
     577        9656 :     PG_END_TRY();
     578             : 
     579        9656 :     return last_res;
     580             : }
     581             : 
     582             : /*
     583             :  * Report an error we got from the remote server.
     584             :  *
     585             :  * elevel: error level to use (typically ERROR, but might be less)
     586             :  * res: PGresult containing the error
     587             :  * conn: connection we did the query on
     588             :  * clear: if true, PQclear the result (otherwise caller will handle it)
     589             :  * sql: NULL, or text of remote command we tried to execute
     590             :  *
     591             :  * Note: callers that choose not to throw ERROR for a remote error are
     592             :  * responsible for making sure that the associated ConnCacheEntry gets
     593             :  * marked with have_error = true.
     594             :  */
     595             : void
     596          18 : pgfdw_report_error(int elevel, PGresult *res, PGconn *conn,
     597             :                    bool clear, const char *sql)
     598             : {
     599             :     /* If requested, PGresult must be released before leaving this function. */
     600          18 :     PG_TRY();
     601             :     {
     602          18 :         char       *diag_sqlstate = PQresultErrorField(res, PG_DIAG_SQLSTATE);
     603          18 :         char       *message_primary = PQresultErrorField(res, PG_DIAG_MESSAGE_PRIMARY);
     604          18 :         char       *message_detail = PQresultErrorField(res, PG_DIAG_MESSAGE_DETAIL);
     605          18 :         char       *message_hint = PQresultErrorField(res, PG_DIAG_MESSAGE_HINT);
     606          18 :         char       *message_context = PQresultErrorField(res, PG_DIAG_CONTEXT);
     607             :         int         sqlstate;
     608             : 
     609          18 :         if (diag_sqlstate)
     610          18 :             sqlstate = MAKE_SQLSTATE(diag_sqlstate[0],
     611             :                                      diag_sqlstate[1],
     612             :                                      diag_sqlstate[2],
     613             :                                      diag_sqlstate[3],
     614             :                                      diag_sqlstate[4]);
     615             :         else
     616           0 :             sqlstate = ERRCODE_CONNECTION_FAILURE;
     617             : 
     618             :         /*
     619             :          * If we don't get a message from the PGresult, try the PGconn.  This
     620             :          * is needed because for connection-level failures, PQexec may just
     621             :          * return NULL, not a PGresult at all.
     622             :          */
     623          18 :         if (message_primary == NULL)
     624           0 :             message_primary = pchomp(PQerrorMessage(conn));
     625             : 
     626          18 :         ereport(elevel,
     627             :                 (errcode(sqlstate),
     628             :                  message_primary ? errmsg_internal("%s", message_primary) :
     629             :                  errmsg("could not obtain message string for remote error"),
     630             :                  message_detail ? errdetail_internal("%s", message_detail) : 0,
     631             :                  message_hint ? errhint("%s", message_hint) : 0,
     632             :                  message_context ? errcontext("%s", message_context) : 0,
     633             :                  sql ? errcontext("remote SQL command: %s", sql) : 0));
     634             :     }
     635          18 :     PG_CATCH();
     636             :     {
     637          18 :         if (clear)
     638          16 :             PQclear(res);
     639          18 :         PG_RE_THROW();
     640             :     }
     641           0 :     PG_END_TRY();
     642           0 :     if (clear)
     643           0 :         PQclear(res);
     644           0 : }
     645             : 
     646             : /*
     647             :  * pgfdw_xact_callback --- cleanup at main-transaction end.
     648             :  */
     649             : static void
     650        4508 : pgfdw_xact_callback(XactEvent event, void *arg)
     651             : {
     652             :     HASH_SEQ_STATUS scan;
     653             :     ConnCacheEntry *entry;
     654             : 
     655             :     /* Quick exit if no connections were touched in this transaction. */
     656        4508 :     if (!xact_got_connection)
     657        3646 :         return;
     658             : 
     659             :     /*
     660             :      * Scan all connection cache entries to find open remote transactions, and
     661             :      * close them.
     662             :      */
     663         862 :     hash_seq_init(&scan, ConnectionHash);
     664        3888 :     while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
     665             :     {
     666             :         PGresult   *res;
     667             : 
     668             :         /* Ignore cache entry if no open connection right now */
     669        2164 :         if (entry->conn == NULL)
     670           4 :             continue;
     671             : 
     672             :         /* If it has an open remote transaction, try to close it */
     673        2160 :         if (entry->xact_depth > 0)
     674             :         {
     675         864 :             bool        abort_cleanup_failure = false;
     676             : 
     677         864 :             elog(DEBUG3, "closing remote transaction on connection %p",
     678             :                  entry->conn);
     679             : 
     680         864 :             switch (event)
     681             :             {
     682             :                 case XACT_EVENT_PARALLEL_PRE_COMMIT:
     683             :                 case XACT_EVENT_PRE_COMMIT:
     684             : 
     685             :                     /*
     686             :                      * If abort cleanup previously failed for this connection,
     687             :                      * we can't issue any more commands against it.
     688             :                      */
     689         830 :                     pgfdw_reject_incomplete_xact_state_change(entry);
     690             : 
     691             :                     /* Commit all remote transactions during pre-commit */
     692         830 :                     entry->changing_xact_state = true;
     693         830 :                     do_sql_command(entry->conn, "COMMIT TRANSACTION");
     694         830 :                     entry->changing_xact_state = false;
     695             : 
     696             :                     /*
     697             :                      * If there were any errors in subtransactions, and we
     698             :                      * made prepared statements, do a DEALLOCATE ALL to make
     699             :                      * sure we get rid of all prepared statements. This is
     700             :                      * annoying and not terribly bulletproof, but it's
     701             :                      * probably not worth trying harder.
     702             :                      *
     703             :                      * DEALLOCATE ALL only exists in 8.3 and later, so this
     704             :                      * constrains how old a server postgres_fdw can
     705             :                      * communicate with.  We intentionally ignore errors in
     706             :                      * the DEALLOCATE, so that we can hobble along to some
     707             :                      * extent with older servers (leaking prepared statements
     708             :                      * as we go; but we don't really support update operations
     709             :                      * pre-8.3 anyway).
     710             :                      */
     711         830 :                     if (entry->have_prep_stmt && entry->have_error)
     712             :                     {
     713           0 :                         res = PQexec(entry->conn, "DEALLOCATE ALL");
     714           0 :                         PQclear(res);
     715             :                     }
     716         830 :                     entry->have_prep_stmt = false;
     717         830 :                     entry->have_error = false;
     718         830 :                     break;
     719             :                 case XACT_EVENT_PRE_PREPARE:
     720             : 
     721             :                     /*
     722             :                      * We disallow remote transactions that modified anything,
     723             :                      * since it's not very reasonable to hold them open until
     724             :                      * the prepared transaction is committed.  For the moment,
     725             :                      * throw error unconditionally; later we might allow
     726             :                      * read-only cases.  Note that the error will cause us to
     727             :                      * come right back here with event == XACT_EVENT_ABORT, so
     728             :                      * we'll clean up the connection state at that point.
     729             :                      */
     730           0 :                     ereport(ERROR,
     731             :                             (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
     732             :                              errmsg("cannot prepare a transaction that modified remote tables")));
     733             :                     break;
     734             :                 case XACT_EVENT_PARALLEL_COMMIT:
     735             :                 case XACT_EVENT_COMMIT:
     736             :                 case XACT_EVENT_PREPARE:
     737             :                     /* Pre-commit should have closed the open transaction */
     738           0 :                     elog(ERROR, "missed cleaning up connection during pre-commit");
     739             :                     break;
     740             :                 case XACT_EVENT_PARALLEL_ABORT:
     741             :                 case XACT_EVENT_ABORT:
     742             : 
     743             :                     /*
     744             :                      * Don't try to clean up the connection if we're already
     745             :                      * in error recursion trouble.
     746             :                      */
     747          34 :                     if (in_error_recursion_trouble())
     748           0 :                         entry->changing_xact_state = true;
     749             : 
     750             :                     /*
     751             :                      * If connection is already unsalvageable, don't touch it
     752             :                      * further.
     753             :                      */
     754          34 :                     if (entry->changing_xact_state)
     755           0 :                         break;
     756             : 
     757             :                     /*
     758             :                      * Mark this connection as in the process of changing
     759             :                      * transaction state.
     760             :                      */
     761          34 :                     entry->changing_xact_state = true;
     762             : 
     763             :                     /* Assume we might have lost track of prepared statements */
     764          34 :                     entry->have_error = true;
     765             : 
     766             :                     /*
     767             :                      * If a command has been submitted to the remote server by
     768             :                      * using an asynchronous execution function, the command
     769             :                      * might not have yet completed.  Check to see if a
     770             :                      * command is still being processed by the remote server,
     771             :                      * and if so, request cancellation of the command.
     772             :                      */
     773          34 :                     if (PQtransactionStatus(entry->conn) == PQTRANS_ACTIVE &&
     774           0 :                         !pgfdw_cancel_query(entry->conn))
     775             :                     {
     776             :                         /* Unable to cancel running query. */
     777           0 :                         abort_cleanup_failure = true;
     778             :                     }
     779          34 :                     else if (!pgfdw_exec_cleanup_query(entry->conn,
     780             :                                                        "ABORT TRANSACTION",
     781             :                                                        false))
     782             :                     {
     783             :                         /* Unable to abort remote transaction. */
     784           0 :                         abort_cleanup_failure = true;
     785             :                     }
     786          48 :                     else if (entry->have_prep_stmt && entry->have_error &&
     787          14 :                              !pgfdw_exec_cleanup_query(entry->conn,
     788             :                                                        "DEALLOCATE ALL",
     789             :                                                        true))
     790             :                     {
     791             :                         /* Trouble clearing prepared statements. */
     792           0 :                         abort_cleanup_failure = true;
     793             :                     }
     794             :                     else
     795             :                     {
     796          34 :                         entry->have_prep_stmt = false;
     797          34 :                         entry->have_error = false;
     798             :                     }
     799             : 
     800             :                     /* Disarm changing_xact_state if it all worked. */
     801          34 :                     entry->changing_xact_state = abort_cleanup_failure;
     802          34 :                     break;
     803             :             }
     804             :         }
     805             : 
     806             :         /* Reset state to show we're out of a transaction */
     807        2160 :         entry->xact_depth = 0;
     808             : 
     809             :         /*
     810             :          * If the connection isn't in a good idle state, discard it to
     811             :          * recover. Next GetConnection will open a new connection.
     812             :          */
     813        4320 :         if (PQstatus(entry->conn) != CONNECTION_OK ||
     814        4320 :             PQtransactionStatus(entry->conn) != PQTRANS_IDLE ||
     815        2160 :             entry->changing_xact_state)
     816             :         {
     817           0 :             elog(DEBUG3, "discarding connection %p", entry->conn);
     818           0 :             disconnect_pg_server(entry);
     819             :         }
     820             :     }
     821             : 
     822             :     /*
     823             :      * Regardless of the event type, we can now mark ourselves as out of the
     824             :      * transaction.  (Note: if we are here during PRE_COMMIT or PRE_PREPARE,
     825             :      * this saves a useless scan of the hashtable during COMMIT or PREPARE.)
     826             :      */
     827         862 :     xact_got_connection = false;
     828             : 
     829             :     /* Also reset cursor numbering for next transaction */
     830         862 :     cursor_number = 0;
     831             : }
     832             : 
     833             : /*
     834             :  * pgfdw_subxact_callback --- cleanup at subtransaction end.
     835             :  */
     836             : static void
     837          46 : pgfdw_subxact_callback(SubXactEvent event, SubTransactionId mySubid,
     838             :                        SubTransactionId parentSubid, void *arg)
     839             : {
     840             :     HASH_SEQ_STATUS scan;
     841             :     ConnCacheEntry *entry;
     842             :     int         curlevel;
     843             : 
     844             :     /* Nothing to do at subxact start, nor after commit. */
     845          46 :     if (!(event == SUBXACT_EVENT_PRE_COMMIT_SUB ||
     846             :           event == SUBXACT_EVENT_ABORT_SUB))
     847          56 :         return;
     848             : 
     849             :     /* Quick exit if no connections were touched in this transaction. */
     850          18 :     if (!xact_got_connection)
     851           0 :         return;
     852             : 
     853             :     /*
     854             :      * Scan all connection cache entries to find open remote subtransactions
     855             :      * of the current level, and close them.
     856             :      */
     857          18 :     curlevel = GetCurrentTransactionNestLevel();
     858          18 :     hash_seq_init(&scan, ConnectionHash);
     859          90 :     while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
     860             :     {
     861             :         char        sql[100];
     862             : 
     863             :         /*
     864             :          * We only care about connections with open remote subtransactions of
     865             :          * the current level.
     866             :          */
     867          54 :         if (entry->conn == NULL || entry->xact_depth < curlevel)
     868          38 :             continue;
     869             : 
     870          16 :         if (entry->xact_depth > curlevel)
     871           0 :             elog(ERROR, "missed cleaning up remote subtransaction at level %d",
     872             :                  entry->xact_depth);
     873             : 
     874          16 :         if (event == SUBXACT_EVENT_PRE_COMMIT_SUB)
     875             :         {
     876             :             /*
     877             :              * If abort cleanup previously failed for this connection, we
     878             :              * can't issue any more commands against it.
     879             :              */
     880          10 :             pgfdw_reject_incomplete_xact_state_change(entry);
     881             : 
     882             :             /* Commit all remote subtransactions during pre-commit */
     883          10 :             snprintf(sql, sizeof(sql), "RELEASE SAVEPOINT s%d", curlevel);
     884          10 :             entry->changing_xact_state = true;
     885          10 :             do_sql_command(entry->conn, sql);
     886          10 :             entry->changing_xact_state = false;
     887             :         }
     888           6 :         else if (in_error_recursion_trouble())
     889             :         {
     890             :             /*
     891             :              * Don't try to clean up the connection if we're already in error
     892             :              * recursion trouble.
     893             :              */
     894           0 :             entry->changing_xact_state = true;
     895             :         }
     896           6 :         else if (!entry->changing_xact_state)
     897             :         {
     898           6 :             bool        abort_cleanup_failure = false;
     899             : 
     900             :             /* Remember that abort cleanup is in progress. */
     901           6 :             entry->changing_xact_state = true;
     902             : 
     903             :             /* Assume we might have lost track of prepared statements */
     904           6 :             entry->have_error = true;
     905             : 
     906             :             /*
     907             :              * If a command has been submitted to the remote server by using
     908             :              * an asynchronous execution function, the command might not have
     909             :              * yet completed.  Check to see if a command is still being
     910             :              * processed by the remote server, and if so, request cancellation
     911             :              * of the command.
     912             :              */
     913           6 :             if (PQtransactionStatus(entry->conn) == PQTRANS_ACTIVE &&
     914           0 :                 !pgfdw_cancel_query(entry->conn))
     915           0 :                 abort_cleanup_failure = true;
     916             :             else
     917             :             {
     918             :                 /* Rollback all remote subtransactions during abort */
     919           6 :                 snprintf(sql, sizeof(sql),
     920             :                          "ROLLBACK TO SAVEPOINT s%d; RELEASE SAVEPOINT s%d",
     921             :                          curlevel, curlevel);
     922           6 :                 if (!pgfdw_exec_cleanup_query(entry->conn, sql, false))
     923           0 :                     abort_cleanup_failure = true;
     924             :             }
     925             : 
     926             :             /* Disarm changing_xact_state if it all worked. */
     927           6 :             entry->changing_xact_state = abort_cleanup_failure;
     928             :         }
     929             : 
     930             :         /* OK, we're outta that level of subtransaction */
     931          16 :         entry->xact_depth--;
     932             :     }
     933             : }
     934             : 
     935             : /*
     936             :  * Connection invalidation callback function
     937             :  *
     938             :  * After a change to a pg_foreign_server or pg_user_mapping catalog entry,
     939             :  * mark connections depending on that entry as needing to be remade.
     940             :  * We can't immediately destroy them, since they might be in the midst of
     941             :  * a transaction, but we'll remake them at the next opportunity.
     942             :  *
     943             :  * Although most cache invalidation callbacks blow away all the related stuff
     944             :  * regardless of the given hashvalue, connections are expensive enough that
     945             :  * it's worth trying to avoid that.
     946             :  *
     947             :  * NB: We could avoid unnecessary disconnection more strictly by examining
     948             :  * individual option values, but it seems too much effort for the gain.
     949             :  */
     950             : static void
     951          46 : pgfdw_inval_callback(Datum arg, int cacheid, uint32 hashvalue)
     952             : {
     953             :     HASH_SEQ_STATUS scan;
     954             :     ConnCacheEntry *entry;
     955             : 
     956             :     Assert(cacheid == FOREIGNSERVEROID || cacheid == USERMAPPINGOID);
     957             : 
     958             :     /* ConnectionHash must exist already, if we're registered */
     959          46 :     hash_seq_init(&scan, ConnectionHash);
     960         196 :     while ((entry = (ConnCacheEntry *) hash_seq_search(&scan)))
     961             :     {
     962             :         /* Ignore invalid entries */
     963         104 :         if (entry->conn == NULL)
     964           6 :             continue;
     965             : 
     966             :         /* hashvalue == 0 means a cache reset, must clear all state */
     967          98 :         if (hashvalue == 0 ||
     968          80 :             (cacheid == FOREIGNSERVEROID &&
     969         138 :              entry->server_hashvalue == hashvalue) ||
     970          18 :             (cacheid == USERMAPPINGOID &&
     971          18 :              entry->mapping_hashvalue == hashvalue))
     972          46 :             entry->invalidated = true;
     973             :     }
     974          46 : }
     975             : 
     976             : /*
     977             :  * Raise an error if the given connection cache entry is marked as being
     978             :  * in the middle of an xact state change.  This should be called at which no
     979             :  * such change is expected to be in progress; if one is found to be in
     980             :  * progress, it means that we aborted in the middle of a previous state change
     981             :  * and now don't know what the remote transaction state actually is.
     982             :  * Such connections can't safely be further used.  Re-establishing the
     983             :  * connection would change the snapshot and roll back any writes already
     984             :  * performed, so that's not an option, either. Thus, we must abort.
     985             :  */
     986             : static void
     987        3466 : pgfdw_reject_incomplete_xact_state_change(ConnCacheEntry *entry)
     988             : {
     989             :     HeapTuple   tup;
     990             :     Form_pg_user_mapping umform;
     991             :     ForeignServer *server;
     992             : 
     993             :     /* nothing to do for inactive entries and entries of sane state */
     994        3466 :     if (entry->conn == NULL || !entry->changing_xact_state)
     995        3466 :         return;
     996             : 
     997             :     /* make sure this entry is inactive */
     998           0 :     disconnect_pg_server(entry);
     999             : 
    1000             :     /* find server name to be shown in the message below */
    1001           0 :     tup = SearchSysCache1(USERMAPPINGOID,
    1002           0 :                           ObjectIdGetDatum(entry->key));
    1003           0 :     if (!HeapTupleIsValid(tup))
    1004           0 :         elog(ERROR, "cache lookup failed for user mapping %u", entry->key);
    1005           0 :     umform = (Form_pg_user_mapping) GETSTRUCT(tup);
    1006           0 :     server = GetForeignServer(umform->umserver);
    1007           0 :     ReleaseSysCache(tup);
    1008             : 
    1009           0 :     ereport(ERROR,
    1010             :             (errcode(ERRCODE_CONNECTION_EXCEPTION),
    1011             :              errmsg("connection to server \"%s\" was lost",
    1012             :                     server->servername)));
    1013             : }
    1014             : 
    1015             : /*
    1016             :  * Cancel the currently-in-progress query (whose query text we do not have)
    1017             :  * and ignore the result.  Returns true if we successfully cancel the query
    1018             :  * and discard any pending result, and false if not.
    1019             :  */
    1020             : static bool
    1021           0 : pgfdw_cancel_query(PGconn *conn)
    1022             : {
    1023             :     PGcancel   *cancel;
    1024             :     char        errbuf[256];
    1025           0 :     PGresult   *result = NULL;
    1026             :     TimestampTz endtime;
    1027             : 
    1028             :     /*
    1029             :      * If it takes too long to cancel the query and discard the result, assume
    1030             :      * the connection is dead.
    1031             :      */
    1032           0 :     endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), 30000);
    1033             : 
    1034             :     /*
    1035             :      * Issue cancel request.  Unfortunately, there's no good way to limit the
    1036             :      * amount of time that we might block inside PQgetCancel().
    1037             :      */
    1038           0 :     if ((cancel = PQgetCancel(conn)))
    1039             :     {
    1040           0 :         if (!PQcancel(cancel, errbuf, sizeof(errbuf)))
    1041             :         {
    1042           0 :             ereport(WARNING,
    1043             :                     (errcode(ERRCODE_CONNECTION_FAILURE),
    1044             :                      errmsg("could not send cancel request: %s",
    1045             :                             errbuf)));
    1046           0 :             PQfreeCancel(cancel);
    1047           0 :             return false;
    1048             :         }
    1049           0 :         PQfreeCancel(cancel);
    1050             :     }
    1051             : 
    1052             :     /* Get and discard the result of the query. */
    1053           0 :     if (pgfdw_get_cleanup_result(conn, endtime, &result))
    1054           0 :         return false;
    1055           0 :     PQclear(result);
    1056             : 
    1057           0 :     return true;
    1058             : }
    1059             : 
    1060             : /*
    1061             :  * Submit a query during (sub)abort cleanup and wait up to 30 seconds for the
    1062             :  * result.  If the query is executed without error, the return value is true.
    1063             :  * If the query is executed successfully but returns an error, the return
    1064             :  * value is true if and only if ignore_errors is set.  If the query can't be
    1065             :  * sent or times out, the return value is false.
    1066             :  */
    1067             : static bool
    1068          54 : pgfdw_exec_cleanup_query(PGconn *conn, const char *query, bool ignore_errors)
    1069             : {
    1070          54 :     PGresult   *result = NULL;
    1071             :     TimestampTz endtime;
    1072             : 
    1073             :     /*
    1074             :      * If it takes too long to execute a cleanup query, assume the connection
    1075             :      * is dead.  It's fairly likely that this is why we aborted in the first
    1076             :      * place (e.g. statement timeout, user cancel), so the timeout shouldn't
    1077             :      * be too long.
    1078             :      */
    1079          54 :     endtime = TimestampTzPlusMilliseconds(GetCurrentTimestamp(), 30000);
    1080             : 
    1081             :     /*
    1082             :      * Submit a query.  Since we don't use non-blocking mode, this also can
    1083             :      * block.  But its risk is relatively small, so we ignore that for now.
    1084             :      */
    1085          54 :     if (!PQsendQuery(conn, query))
    1086             :     {
    1087           0 :         pgfdw_report_error(WARNING, NULL, conn, false, query);
    1088           0 :         return false;
    1089             :     }
    1090             : 
    1091             :     /* Get the result of the query. */
    1092          54 :     if (pgfdw_get_cleanup_result(conn, endtime, &result))
    1093           0 :         return false;
    1094             : 
    1095             :     /* Issue a warning if not successful. */
    1096          54 :     if (PQresultStatus(result) != PGRES_COMMAND_OK)
    1097             :     {
    1098           0 :         pgfdw_report_error(WARNING, result, conn, true, query);
    1099           0 :         return ignore_errors;
    1100             :     }
    1101          54 :     PQclear(result);
    1102             : 
    1103          54 :     return true;
    1104             : }
    1105             : 
    1106             : /*
    1107             :  * Get, during abort cleanup, the result of a query that is in progress.  This
    1108             :  * might be a query that is being interrupted by transaction abort, or it might
    1109             :  * be a query that was initiated as part of transaction abort to get the remote
    1110             :  * side back to the appropriate state.
    1111             :  *
    1112             :  * It's not a huge problem if we throw an ERROR here, but if we get into error
    1113             :  * recursion trouble, we'll end up slamming the connection shut, which will
    1114             :  * necessitate failing the entire toplevel transaction even if subtransactions
    1115             :  * were used.  Try to use WARNING where we can.
    1116             :  *
    1117             :  * endtime is the time at which we should give up and assume the remote
    1118             :  * side is dead.  Returns true if the timeout expired, otherwise false.
    1119             :  * Sets *result except in case of a timeout.
    1120             :  */
    1121             : static bool
    1122          54 : pgfdw_get_cleanup_result(PGconn *conn, TimestampTz endtime, PGresult **result)
    1123             : {
    1124          54 :     volatile bool timed_out = false;
    1125          54 :     PGresult   *volatile last_res = NULL;
    1126             : 
    1127             :     /* In what follows, do not leak any PGresults on an error. */
    1128          54 :     PG_TRY();
    1129             :     {
    1130             :         for (;;)
    1131          60 :         {
    1132             :             PGresult   *res;
    1133             : 
    1134         282 :             while (PQisBusy(conn))
    1135             :             {
    1136             :                 int         wc;
    1137          54 :                 TimestampTz now = GetCurrentTimestamp();
    1138             :                 long        secs;
    1139             :                 int         microsecs;
    1140             :                 long        cur_timeout;
    1141             : 
    1142             :                 /* If timeout has expired, give up, else get sleep time. */
    1143          54 :                 if (now >= endtime)
    1144             :                 {
    1145           0 :                     timed_out = true;
    1146           0 :                     goto exit;
    1147             :                 }
    1148          54 :                 TimestampDifference(now, endtime, &secs, &microsecs);
    1149             : 
    1150             :                 /* To protect against clock skew, limit sleep to one minute. */
    1151          54 :                 cur_timeout = Min(60000, secs * USECS_PER_SEC + microsecs);
    1152             : 
    1153             :                 /* Sleep until there's something to do */
    1154          54 :                 wc = WaitLatchOrSocket(MyLatch,
    1155             :                                        WL_LATCH_SET | WL_SOCKET_READABLE | WL_TIMEOUT,
    1156             :                                        PQsocket(conn),
    1157             :                                        cur_timeout, PG_WAIT_EXTENSION);
    1158          54 :                 ResetLatch(MyLatch);
    1159             : 
    1160          54 :                 CHECK_FOR_INTERRUPTS();
    1161             : 
    1162             :                 /* Data available in socket? */
    1163          54 :                 if (wc & WL_SOCKET_READABLE)
    1164             :                 {
    1165          54 :                     if (!PQconsumeInput(conn))
    1166             :                     {
    1167             :                         /* connection trouble; treat the same as a timeout */
    1168           0 :                         timed_out = true;
    1169           0 :                         goto exit;
    1170             :                     }
    1171             :                 }
    1172             :             }
    1173             : 
    1174         114 :             res = PQgetResult(conn);
    1175         114 :             if (res == NULL)
    1176          54 :                 break;          /* query is complete */
    1177             : 
    1178          60 :             PQclear(last_res);
    1179          60 :             last_res = res;
    1180             :         }
    1181             : exit:   ;
    1182             :     }
    1183           0 :     PG_CATCH();
    1184             :     {
    1185           0 :         PQclear(last_res);
    1186           0 :         PG_RE_THROW();
    1187             :     }
    1188          54 :     PG_END_TRY();
    1189             : 
    1190          54 :     if (timed_out)
    1191           0 :         PQclear(last_res);
    1192             :     else
    1193          54 :         *result = last_res;
    1194          54 :     return timed_out;
    1195             : }

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