Line data Source code
1 : /*-------------------------------------------------------------------------
2 : *
3 : * pmchild.c
4 : * Functions for keeping track of postmaster child processes.
5 : *
6 : * Postmaster keeps track of all child processes so that when a process exits,
7 : * it knows what kind of a process it was and can clean up accordingly. Every
8 : * child process is allocated a PMChild struct from a fixed pool of structs.
9 : * The size of the pool is determined by various settings that configure how
10 : * many worker processes and backend connections are allowed, i.e.
11 : * autovacuum_worker_slots, max_worker_processes, max_wal_senders, and
12 : * max_connections.
13 : *
14 : * Dead-end backends are handled slightly differently. There is no limit
15 : * on the number of dead-end backends, and they do not need unique IDs, so
16 : * their PMChild structs are allocated dynamically, not from a pool.
17 : *
18 : * The structures and functions in this file are private to the postmaster
19 : * process. But note that there is an array in shared memory, managed by
20 : * pmsignal.c, that mirrors this.
21 : *
22 : *
23 : * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
24 : * Portions Copyright (c) 1994, Regents of the University of California
25 : *
26 : * IDENTIFICATION
27 : * src/backend/postmaster/pmchild.c
28 : *
29 : *-------------------------------------------------------------------------
30 : */
31 :
32 : #include "postgres.h"
33 :
34 : #include "miscadmin.h"
35 : #include "postmaster/autovacuum.h"
36 : #include "postmaster/postmaster.h"
37 : #include "replication/walsender.h"
38 : #include "storage/pmsignal.h"
39 : #include "storage/proc.h"
40 :
41 : /*
42 : * Freelists for different kinds of child processes. We maintain separate
43 : * pools for each, so that for example launching a lot of regular backends
44 : * cannot prevent autovacuum or an aux process from launching.
45 : */
46 : typedef struct PMChildPool
47 : {
48 : int size; /* number of PMChild slots reserved for this
49 : * kind of processes */
50 : int first_slotno; /* first slot belonging to this pool */
51 : dlist_head freelist; /* currently unused PMChild entries */
52 : } PMChildPool;
53 :
54 : static PMChildPool pmchild_pools[BACKEND_NUM_TYPES];
55 : NON_EXEC_STATIC int num_pmchild_slots = 0;
56 :
57 : /*
58 : * List of active child processes. This includes dead-end children.
59 : */
60 : dlist_head ActiveChildList;
61 :
62 : /*
63 : * Dummy pointer to persuade Valgrind that we've not leaked the array of
64 : * PMChild structs. Make it global to ensure the compiler doesn't
65 : * optimize it away.
66 : */
67 : #ifdef USE_VALGRIND
68 : extern PMChild *pmchild_array;
69 : PMChild *pmchild_array;
70 : #endif
71 :
72 :
73 : /*
74 : * MaxLivePostmasterChildren
75 : *
76 : * This reports the number of postmaster child processes that can be active.
77 : * It includes all children except for dead-end children. This allows the
78 : * array in shared memory (PMChildFlags) to have a fixed maximum size.
79 : */
80 : int
81 5642 : MaxLivePostmasterChildren(void)
82 : {
83 5642 : if (num_pmchild_slots == 0)
84 0 : elog(ERROR, "PM child array not initialized yet");
85 5642 : return num_pmchild_slots;
86 : }
87 :
88 : /*
89 : * Initialize at postmaster startup
90 : *
91 : * Note: This is not called on crash restart. We rely on PMChild entries to
92 : * remain valid through the restart process. This is important because the
93 : * syslogger survives through the crash restart process, so we must not
94 : * invalidate its PMChild slot.
95 : */
96 : void
97 1157 : InitPostmasterChildSlots(void)
98 : {
99 : int slotno;
100 : PMChild *slots;
101 :
102 : /*
103 : * We allow more connections here than we can have backends because some
104 : * might still be authenticating; they might fail auth, or some existing
105 : * backend might exit before the auth cycle is completed. The exact
106 : * MaxConnections limit is enforced when a new backend tries to join the
107 : * PGPROC array.
108 : *
109 : * WAL senders start out as regular backends, so they share the same pool.
110 : */
111 1157 : pmchild_pools[B_BACKEND].size = 2 * (MaxConnections + max_wal_senders);
112 :
113 1157 : pmchild_pools[B_AUTOVAC_WORKER].size = autovacuum_worker_slots;
114 1157 : pmchild_pools[B_BG_WORKER].size = max_worker_processes;
115 1157 : pmchild_pools[B_IO_WORKER].size = MAX_IO_WORKERS;
116 :
117 : /*
118 : * There can be only one of each of these running at a time. They each
119 : * get their own pool of just one entry.
120 : */
121 1157 : pmchild_pools[B_AUTOVAC_LAUNCHER].size = 1;
122 1157 : pmchild_pools[B_SLOTSYNC_WORKER].size = 1;
123 1157 : pmchild_pools[B_ARCHIVER].size = 1;
124 1157 : pmchild_pools[B_BG_WRITER].size = 1;
125 1157 : pmchild_pools[B_CHECKPOINTER].size = 1;
126 1157 : pmchild_pools[B_STARTUP].size = 1;
127 1157 : pmchild_pools[B_WAL_RECEIVER].size = 1;
128 1157 : pmchild_pools[B_WAL_SUMMARIZER].size = 1;
129 1157 : pmchild_pools[B_WAL_WRITER].size = 1;
130 1157 : pmchild_pools[B_LOGGER].size = 1;
131 :
132 : /* The rest of the pmchild_pools are left at zero size */
133 :
134 : /* Count the total number of slots */
135 1157 : num_pmchild_slots = 0;
136 21983 : for (int i = 0; i < BACKEND_NUM_TYPES; i++)
137 20826 : num_pmchild_slots += pmchild_pools[i].size;
138 :
139 : /* Allocate enough slots, and make sure Valgrind doesn't complain */
140 1157 : slots = palloc(num_pmchild_slots * sizeof(PMChild));
141 : #ifdef USE_VALGRIND
142 : pmchild_array = slots;
143 : #endif
144 :
145 : /* Initialize them */
146 1157 : slotno = 0;
147 21983 : for (int btype = 0; btype < BACKEND_NUM_TYPES; btype++)
148 : {
149 20826 : pmchild_pools[btype].first_slotno = slotno + 1;
150 20826 : dlist_init(&pmchild_pools[btype].freelist);
151 :
152 256541 : for (int j = 0; j < pmchild_pools[btype].size; j++)
153 : {
154 235715 : slots[slotno].pid = 0;
155 235715 : slots[slotno].child_slot = slotno + 1;
156 235715 : slots[slotno].bkend_type = B_INVALID;
157 235715 : slots[slotno].rw = NULL;
158 235715 : slots[slotno].bgworker_notify = false;
159 235715 : dlist_push_tail(&pmchild_pools[btype].freelist, &slots[slotno].elem);
160 235715 : slotno++;
161 : }
162 : }
163 : Assert(slotno == num_pmchild_slots);
164 :
165 : /* Initialize other structures */
166 1157 : dlist_init(&ActiveChildList);
167 1157 : }
168 :
169 : /*
170 : * Allocate a PMChild entry for a postmaster child process of given type.
171 : *
172 : * The entry is taken from the right pool for the type.
173 : *
174 : * pmchild->child_slot in the returned struct is unique among all active child
175 : * processes.
176 : */
177 : PMChild *
178 26636 : AssignPostmasterChildSlot(BackendType btype)
179 : {
180 : dlist_head *freelist;
181 : PMChild *pmchild;
182 :
183 26636 : if (pmchild_pools[btype].size == 0)
184 0 : elog(ERROR, "cannot allocate a PMChild slot for backend type %d", btype);
185 :
186 26636 : freelist = &pmchild_pools[btype].freelist;
187 26636 : if (dlist_is_empty(freelist))
188 28 : return NULL;
189 :
190 26608 : pmchild = dlist_container(PMChild, elem, dlist_pop_head_node(freelist));
191 26608 : pmchild->pid = 0;
192 26608 : pmchild->bkend_type = btype;
193 26608 : pmchild->rw = NULL;
194 26608 : pmchild->bgworker_notify = true;
195 :
196 : /*
197 : * pmchild->child_slot for each entry was initialized when the array of
198 : * slots was allocated. Sanity check it.
199 : */
200 26608 : if (!(pmchild->child_slot >= pmchild_pools[btype].first_slotno &&
201 26608 : pmchild->child_slot < pmchild_pools[btype].first_slotno + pmchild_pools[btype].size))
202 : {
203 0 : elog(ERROR, "pmchild freelist for backend type %d is corrupt",
204 : pmchild->bkend_type);
205 : }
206 :
207 26608 : dlist_push_head(&ActiveChildList, &pmchild->elem);
208 :
209 : /* Update the status in the shared memory array */
210 26608 : MarkPostmasterChildSlotAssigned(pmchild->child_slot);
211 :
212 26608 : elog(DEBUG2, "assigned pm child slot %d for %s",
213 : pmchild->child_slot, PostmasterChildName(btype));
214 :
215 26608 : return pmchild;
216 : }
217 :
218 : /*
219 : * Allocate a PMChild struct for a dead-end backend. Dead-end children are
220 : * not assigned a child_slot number. The struct is palloc'd; returns NULL if
221 : * out of memory.
222 : */
223 : PMChild *
224 238 : AllocDeadEndChild(void)
225 : {
226 : PMChild *pmchild;
227 :
228 238 : elog(DEBUG2, "allocating dead-end child");
229 :
230 238 : pmchild = (PMChild *) palloc_extended(sizeof(PMChild), MCXT_ALLOC_NO_OOM);
231 238 : if (pmchild)
232 : {
233 238 : pmchild->pid = 0;
234 238 : pmchild->child_slot = 0;
235 238 : pmchild->bkend_type = B_DEAD_END_BACKEND;
236 238 : pmchild->rw = NULL;
237 238 : pmchild->bgworker_notify = false;
238 :
239 238 : dlist_push_head(&ActiveChildList, &pmchild->elem);
240 : }
241 :
242 238 : return pmchild;
243 : }
244 :
245 : /*
246 : * Release a PMChild slot, after the child process has exited.
247 : *
248 : * Returns true if the child detached cleanly from shared memory, false
249 : * otherwise (see MarkPostmasterChildSlotUnassigned).
250 : */
251 : bool
252 26825 : ReleasePostmasterChildSlot(PMChild *pmchild)
253 : {
254 26825 : dlist_delete(&pmchild->elem);
255 26825 : if (pmchild->bkend_type == B_DEAD_END_BACKEND)
256 : {
257 238 : elog(DEBUG2, "releasing dead-end backend");
258 238 : pfree(pmchild);
259 238 : return true;
260 : }
261 : else
262 : {
263 : PMChildPool *pool;
264 :
265 26587 : elog(DEBUG2, "releasing pm child slot %d", pmchild->child_slot);
266 :
267 : /* WAL senders start out as regular backends, and share the pool */
268 26587 : if (pmchild->bkend_type == B_WAL_SENDER)
269 43 : pool = &pmchild_pools[B_BACKEND];
270 : else
271 26544 : pool = &pmchild_pools[pmchild->bkend_type];
272 :
273 : /* sanity check that we return the entry to the right pool */
274 26587 : if (!(pmchild->child_slot >= pool->first_slotno &&
275 26587 : pmchild->child_slot < pool->first_slotno + pool->size))
276 : {
277 0 : elog(ERROR, "pmchild freelist for backend type %d is corrupt",
278 : pmchild->bkend_type);
279 : }
280 :
281 26587 : dlist_push_head(&pool->freelist, &pmchild->elem);
282 26587 : return MarkPostmasterChildSlotUnassigned(pmchild->child_slot);
283 : }
284 : }
285 :
286 : /*
287 : * Find the PMChild entry of a running child process by PID.
288 : */
289 : PMChild *
290 19351 : FindPostmasterChildByPid(int pid)
291 : {
292 : dlist_iter iter;
293 :
294 42699 : dlist_foreach(iter, &ActiveChildList)
295 : {
296 42699 : PMChild *bp = dlist_container(PMChild, elem, iter.cur);
297 :
298 42699 : if (bp->pid == pid)
299 19351 : return bp;
300 : }
301 0 : return NULL;
302 : }
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