Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * pgstatapprox.c
4 : * Bloat estimation functions
5 : *
6 : * Copyright (c) 2014-2024, PostgreSQL Global Development Group
7 : *
8 : * IDENTIFICATION
9 : * contrib/pgstattuple/pgstatapprox.c
10 : *
11 : *-------------------------------------------------------------------------
12 : */
13 : #include "postgres.h"
14 :
15 : #include "access/heapam.h"
16 : #include "access/htup_details.h"
17 : #include "access/multixact.h"
18 : #include "access/relation.h"
19 : #include "access/transam.h"
20 : #include "access/visibilitymap.h"
21 : #include "access/xact.h"
22 : #include "catalog/namespace.h"
23 : #include "catalog/pg_am_d.h"
24 : #include "commands/vacuum.h"
25 : #include "funcapi.h"
26 : #include "miscadmin.h"
27 : #include "storage/bufmgr.h"
28 : #include "storage/freespace.h"
29 : #include "storage/lmgr.h"
30 : #include "storage/procarray.h"
31 : #include "utils/builtins.h"
32 :
33 2 : PG_FUNCTION_INFO_V1(pgstattuple_approx);
34 4 : PG_FUNCTION_INFO_V1(pgstattuple_approx_v1_5);
35 :
36 : Datum pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo);
37 :
38 : typedef struct output_type
39 : {
40 : uint64 table_len;
41 : double scanned_percent;
42 : uint64 tuple_count;
43 : uint64 tuple_len;
44 : double tuple_percent;
45 : uint64 dead_tuple_count;
46 : uint64 dead_tuple_len;
47 : double dead_tuple_percent;
48 : uint64 free_space;
49 : double free_percent;
50 : } output_type;
51 :
52 : #define NUM_OUTPUT_COLUMNS 10
53 :
54 : /*
55 : * This function takes an already open relation and scans its pages,
56 : * skipping those that have the corresponding visibility map bit set.
57 : * For pages we skip, we find the free space from the free space map
58 : * and approximate tuple_len on that basis. For the others, we count
59 : * the exact number of dead tuples etc.
60 : *
61 : * This scan is loosely based on vacuumlazy.c:lazy_scan_heap(), but
62 : * we do not try to avoid skipping single pages.
63 : */
64 : static void
65 4 : statapprox_heap(Relation rel, output_type *stat)
66 : {
67 : BlockNumber scanned,
68 : nblocks,
69 : blkno;
70 4 : Buffer vmbuffer = InvalidBuffer;
71 : BufferAccessStrategy bstrategy;
72 : TransactionId OldestXmin;
73 :
74 4 : OldestXmin = GetOldestNonRemovableTransactionId(rel);
75 4 : bstrategy = GetAccessStrategy(BAS_BULKREAD);
76 :
77 4 : nblocks = RelationGetNumberOfBlocks(rel);
78 4 : scanned = 0;
79 :
80 4 : for (blkno = 0; blkno < nblocks; blkno++)
81 : {
82 : Buffer buf;
83 : Page page;
84 : OffsetNumber offnum,
85 : maxoff;
86 : Size freespace;
87 :
88 0 : CHECK_FOR_INTERRUPTS();
89 :
90 : /*
91 : * If the page has only visible tuples, then we can find out the free
92 : * space from the FSM and move on.
93 : */
94 0 : if (VM_ALL_VISIBLE(rel, blkno, &vmbuffer))
95 : {
96 0 : freespace = GetRecordedFreeSpace(rel, blkno);
97 0 : stat->tuple_len += BLCKSZ - freespace;
98 0 : stat->free_space += freespace;
99 0 : continue;
100 : }
101 :
102 0 : buf = ReadBufferExtended(rel, MAIN_FORKNUM, blkno,
103 : RBM_NORMAL, bstrategy);
104 :
105 0 : LockBuffer(buf, BUFFER_LOCK_SHARE);
106 :
107 0 : page = BufferGetPage(buf);
108 :
109 : /*
110 : * It's not safe to call PageGetHeapFreeSpace() on new pages, so we
111 : * treat them as being free space for our purposes.
112 : */
113 0 : if (!PageIsNew(page))
114 0 : stat->free_space += PageGetHeapFreeSpace(page);
115 : else
116 0 : stat->free_space += BLCKSZ - SizeOfPageHeaderData;
117 :
118 : /* We may count the page as scanned even if it's new/empty */
119 0 : scanned++;
120 :
121 0 : if (PageIsNew(page) || PageIsEmpty(page))
122 : {
123 0 : UnlockReleaseBuffer(buf);
124 0 : continue;
125 : }
126 :
127 : /*
128 : * Look at each tuple on the page and decide whether it's live or
129 : * dead, then count it and its size. Unlike lazy_scan_heap, we can
130 : * afford to ignore problems and special cases.
131 : */
132 0 : maxoff = PageGetMaxOffsetNumber(page);
133 :
134 0 : for (offnum = FirstOffsetNumber;
135 : offnum <= maxoff;
136 0 : offnum = OffsetNumberNext(offnum))
137 : {
138 : ItemId itemid;
139 : HeapTupleData tuple;
140 :
141 0 : itemid = PageGetItemId(page, offnum);
142 :
143 0 : if (!ItemIdIsUsed(itemid) || ItemIdIsRedirected(itemid) ||
144 0 : ItemIdIsDead(itemid))
145 : {
146 0 : continue;
147 : }
148 :
149 : Assert(ItemIdIsNormal(itemid));
150 :
151 0 : ItemPointerSet(&(tuple.t_self), blkno, offnum);
152 :
153 0 : tuple.t_data = (HeapTupleHeader) PageGetItem(page, itemid);
154 0 : tuple.t_len = ItemIdGetLength(itemid);
155 0 : tuple.t_tableOid = RelationGetRelid(rel);
156 :
157 : /*
158 : * We follow VACUUM's lead in counting INSERT_IN_PROGRESS tuples
159 : * as "dead" while DELETE_IN_PROGRESS tuples are "live". We don't
160 : * bother distinguishing tuples inserted/deleted by our own
161 : * transaction.
162 : */
163 0 : switch (HeapTupleSatisfiesVacuum(&tuple, OldestXmin, buf))
164 : {
165 0 : case HEAPTUPLE_LIVE:
166 : case HEAPTUPLE_DELETE_IN_PROGRESS:
167 0 : stat->tuple_len += tuple.t_len;
168 0 : stat->tuple_count++;
169 0 : break;
170 0 : case HEAPTUPLE_DEAD:
171 : case HEAPTUPLE_RECENTLY_DEAD:
172 : case HEAPTUPLE_INSERT_IN_PROGRESS:
173 0 : stat->dead_tuple_len += tuple.t_len;
174 0 : stat->dead_tuple_count++;
175 0 : break;
176 0 : default:
177 0 : elog(ERROR, "unexpected HeapTupleSatisfiesVacuum result");
178 : break;
179 : }
180 : }
181 :
182 0 : UnlockReleaseBuffer(buf);
183 : }
184 :
185 4 : stat->table_len = (uint64) nblocks * BLCKSZ;
186 :
187 : /*
188 : * We don't know how many tuples are in the pages we didn't scan, so
189 : * extrapolate the live-tuple count to the whole table in the same way
190 : * that VACUUM does. (Like VACUUM, we're not taking a random sample, so
191 : * just extrapolating linearly seems unsafe.) There should be no dead
192 : * tuples in all-visible pages, so no correction is needed for that, and
193 : * we already accounted for the space in those pages, too.
194 : */
195 8 : stat->tuple_count = vac_estimate_reltuples(rel, nblocks, scanned,
196 4 : stat->tuple_count);
197 :
198 : /* It's not clear if we could get -1 here, but be safe. */
199 4 : stat->tuple_count = Max(stat->tuple_count, 0);
200 :
201 : /*
202 : * Calculate percentages if the relation has one or more pages.
203 : */
204 4 : if (nblocks != 0)
205 : {
206 0 : stat->scanned_percent = 100.0 * scanned / nblocks;
207 0 : stat->tuple_percent = 100.0 * stat->tuple_len / stat->table_len;
208 0 : stat->dead_tuple_percent = 100.0 * stat->dead_tuple_len / stat->table_len;
209 0 : stat->free_percent = 100.0 * stat->free_space / stat->table_len;
210 : }
211 :
212 4 : if (BufferIsValid(vmbuffer))
213 : {
214 0 : ReleaseBuffer(vmbuffer);
215 0 : vmbuffer = InvalidBuffer;
216 : }
217 4 : }
218 :
219 : /*
220 : * Returns estimated live/dead tuple statistics for the given relid.
221 : *
222 : * The superuser() check here must be kept as the library might be upgraded
223 : * without the extension being upgraded, meaning that in pre-1.5 installations
224 : * these functions could be called by any user.
225 : */
226 : Datum
227 0 : pgstattuple_approx(PG_FUNCTION_ARGS)
228 : {
229 0 : Oid relid = PG_GETARG_OID(0);
230 :
231 0 : if (!superuser())
232 0 : ereport(ERROR,
233 : (errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
234 : errmsg("must be superuser to use pgstattuple functions")));
235 :
236 0 : PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
237 : }
238 :
239 : /*
240 : * As of pgstattuple version 1.5, we no longer need to check if the user
241 : * is a superuser because we REVOKE EXECUTE on the SQL function from PUBLIC.
242 : * Users can then grant access to it based on their policies.
243 : *
244 : * Otherwise identical to pgstattuple_approx (above).
245 : */
246 : Datum
247 10 : pgstattuple_approx_v1_5(PG_FUNCTION_ARGS)
248 : {
249 10 : Oid relid = PG_GETARG_OID(0);
250 :
251 10 : PG_RETURN_DATUM(pgstattuple_approx_internal(relid, fcinfo));
252 : }
253 :
254 : Datum
255 10 : pgstattuple_approx_internal(Oid relid, FunctionCallInfo fcinfo)
256 : {
257 : Relation rel;
258 10 : output_type stat = {0};
259 : TupleDesc tupdesc;
260 : bool nulls[NUM_OUTPUT_COLUMNS];
261 : Datum values[NUM_OUTPUT_COLUMNS];
262 : HeapTuple ret;
263 10 : int i = 0;
264 :
265 10 : if (get_call_result_type(fcinfo, NULL, &tupdesc) != TYPEFUNC_COMPOSITE)
266 0 : elog(ERROR, "return type must be a row type");
267 :
268 10 : if (tupdesc->natts != NUM_OUTPUT_COLUMNS)
269 0 : elog(ERROR, "incorrect number of output arguments");
270 :
271 10 : rel = relation_open(relid, AccessShareLock);
272 :
273 : /*
274 : * Reject attempts to read non-local temporary relations; we would be
275 : * likely to get wrong data since we have no visibility into the owning
276 : * session's local buffers.
277 : */
278 10 : if (RELATION_IS_OTHER_TEMP(rel))
279 0 : ereport(ERROR,
280 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
281 : errmsg("cannot access temporary tables of other sessions")));
282 :
283 : /*
284 : * We support only relation kinds with a visibility map and a free space
285 : * map.
286 : */
287 10 : if (!(rel->rd_rel->relkind == RELKIND_RELATION ||
288 8 : rel->rd_rel->relkind == RELKIND_MATVIEW ||
289 8 : rel->rd_rel->relkind == RELKIND_TOASTVALUE))
290 6 : ereport(ERROR,
291 : (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
292 : errmsg("relation \"%s\" is of wrong relation kind",
293 : RelationGetRelationName(rel)),
294 : errdetail_relkind_not_supported(rel->rd_rel->relkind)));
295 :
296 4 : if (rel->rd_rel->relam != HEAP_TABLE_AM_OID)
297 0 : ereport(ERROR, (errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
298 : errmsg("only heap AM is supported")));
299 :
300 4 : statapprox_heap(rel, &stat);
301 :
302 4 : relation_close(rel, AccessShareLock);
303 :
304 4 : memset(nulls, 0, sizeof(nulls));
305 :
306 4 : values[i++] = Int64GetDatum(stat.table_len);
307 4 : values[i++] = Float8GetDatum(stat.scanned_percent);
308 4 : values[i++] = Int64GetDatum(stat.tuple_count);
309 4 : values[i++] = Int64GetDatum(stat.tuple_len);
310 4 : values[i++] = Float8GetDatum(stat.tuple_percent);
311 4 : values[i++] = Int64GetDatum(stat.dead_tuple_count);
312 4 : values[i++] = Int64GetDatum(stat.dead_tuple_len);
313 4 : values[i++] = Float8GetDatum(stat.dead_tuple_percent);
314 4 : values[i++] = Int64GetDatum(stat.free_space);
315 4 : values[i++] = Float8GetDatum(stat.free_percent);
316 :
317 4 : ret = heap_form_tuple(tupdesc, values, nulls);
318 4 : return HeapTupleGetDatum(ret);
319 : }
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