From 13752743bf7010f7cbf07bdf2a0087c3960121c5 Mon Sep 17 00:00:00 2001 From: Andrew Dunstan Date: Wed, 1 Feb 2017 17:52:35 -0500 Subject: [PATCH] Don't count background workers against a user's connection limit. Doing so doesn't seem to be within the purpose of the per user connection limits, and has particularly unfortunate effects in conjunction with parallel queries. Backpatch to 9.6 where parallel queries were introduced. David Rowley, reviewed by Robert Haas and Albe Laurenz. --- doc/src/sgml/ref/create_database.sgml | 3 ++- doc/src/sgml/ref/create_role.sgml | 5 +++- src/backend/access/transam/twophase.c | 1 + src/backend/storage/ipc/procarray.c | 34 +++++++++++++++++++++++++++ src/backend/storage/lmgr/proc.c | 2 ++ src/backend/utils/init/postinit.c | 2 +- src/include/storage/proc.h | 2 ++ src/include/storage/procarray.h | 1 + 8 files changed, 47 insertions(+), 3 deletions(-) diff --git a/doc/src/sgml/ref/create_database.sgml b/doc/src/sgml/ref/create_database.sgml index cf33746c1e2..cf0d53b3014 100644 --- a/doc/src/sgml/ref/create_database.sgml +++ b/doc/src/sgml/ref/create_database.sgml @@ -258,7 +258,8 @@ CREATE DATABASE name The CONNECTION LIMIT option is only enforced approximately; if two new sessions start at about the same time when just one connection slot remains for the database, it is possible that - both will fail. Also, the limit is not enforced against superusers. + both will fail. Also, the limit is not enforced against superusers or + background worker processes. diff --git a/doc/src/sgml/ref/create_role.sgml b/doc/src/sgml/ref/create_role.sgml index a3b8ed9ab4c..2ae576ede69 100644 --- a/doc/src/sgml/ref/create_role.sgml +++ b/doc/src/sgml/ref/create_role.sgml @@ -198,7 +198,10 @@ CREATE ROLE name [ [ WITH ] If role can log in, this specifies how many concurrent connections - the role can make. -1 (the default) means no limit. + the role can make. -1 (the default) means no limit. Note that only + normal connections are counted towards this limit. Neither prepared + transactions nor background worker connections are counted towards + this limit. diff --git a/src/backend/access/transam/twophase.c b/src/backend/access/transam/twophase.c index 5415604993a..ea7bfa0578b 100644 --- a/src/backend/access/transam/twophase.c +++ b/src/backend/access/transam/twophase.c @@ -420,6 +420,7 @@ MarkAsPreparing(TransactionId xid, const char *gid, proc->backendId = InvalidBackendId; proc->databaseId = databaseid; proc->roleId = owner; + proc->isBackgroundWorker = false; proc->lwWaiting = false; proc->lwWaitMode = 0; proc->waitLock = NULL; diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c index 4adb286d5b5..651c561dfd5 100644 --- a/src/backend/storage/ipc/procarray.c +++ b/src/backend/storage/ipc/procarray.c @@ -2751,6 +2751,38 @@ CountDBBackends(Oid databaseid) return count; } +/* + * CountDBConnections --- counts database backends ignoring any background + * worker processes + */ +int +CountDBConnections(Oid databaseid) +{ + ProcArrayStruct *arrayP = procArray; + int count = 0; + int index; + + LWLockAcquire(ProcArrayLock, LW_SHARED); + + for (index = 0; index < arrayP->numProcs; index++) + { + int pgprocno = arrayP->pgprocnos[index]; + volatile PGPROC *proc = &allProcs[pgprocno]; + + if (proc->pid == 0) + continue; /* do not count prepared xacts */ + if (proc->isBackgroundWorker) + continue; /* do not count background workers */ + if (!OidIsValid(databaseid) || + proc->databaseId == databaseid) + count++; + } + + LWLockRelease(ProcArrayLock); + + return count; +} + /* * CancelDBBackends --- cancel backends that are using specified database */ @@ -2810,6 +2842,8 @@ CountUserBackends(Oid roleid) if (proc->pid == 0) continue; /* do not count prepared xacts */ + if (proc->isBackgroundWorker) + continue; /* do not count background workers */ if (proc->roleId == roleid) count++; } diff --git a/src/backend/storage/lmgr/proc.c b/src/backend/storage/lmgr/proc.c index 9a758bd9160..cb6e1e3e5bc 100644 --- a/src/backend/storage/lmgr/proc.c +++ b/src/backend/storage/lmgr/proc.c @@ -372,6 +372,7 @@ InitProcess(void) MyProc->backendId = InvalidBackendId; MyProc->databaseId = InvalidOid; MyProc->roleId = InvalidOid; + MyProc->isBackgroundWorker = IsBackgroundWorker; MyPgXact->delayChkpt = false; MyPgXact->vacuumFlags = 0; /* NB -- autovac launcher intentionally does not set IS_AUTOVACUUM */ @@ -544,6 +545,7 @@ InitAuxiliaryProcess(void) MyProc->backendId = InvalidBackendId; MyProc->databaseId = InvalidOid; MyProc->roleId = InvalidOid; + MyProc->isBackgroundWorker = IsBackgroundWorker; MyPgXact->delayChkpt = false; MyPgXact->vacuumFlags = 0; MyProc->lwWaiting = false; diff --git a/src/backend/utils/init/postinit.c b/src/backend/utils/init/postinit.c index 824d5abf11f..cde4a798b62 100644 --- a/src/backend/utils/init/postinit.c +++ b/src/backend/utils/init/postinit.c @@ -350,7 +350,7 @@ CheckMyDatabase(const char *name, bool am_superuser) */ if (dbform->datconnlimit >= 0 && !am_superuser && - CountDBBackends(MyDatabaseId) > dbform->datconnlimit) + CountDBConnections(MyDatabaseId) > dbform->datconnlimit) ereport(FATAL, (errcode(ERRCODE_TOO_MANY_CONNECTIONS), errmsg("too many connections for database \"%s\"", diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h index 775c66a1971..c44d82b90c0 100644 --- a/src/include/storage/proc.h +++ b/src/include/storage/proc.h @@ -102,6 +102,8 @@ struct PGPROC Oid databaseId; /* OID of database this backend is using */ Oid roleId; /* OID of role using this backend */ + bool isBackgroundWorker; /* true if background worker. */ + /* * While in hot standby mode, shows that a conflict signal has been sent * for the current transaction. Set/cleared while holding ProcArrayLock, diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h index dd37c0cb070..ecc3c4a4f63 100644 --- a/src/include/storage/procarray.h +++ b/src/include/storage/procarray.h @@ -73,6 +73,7 @@ extern pid_t CancelVirtualTransaction(VirtualTransactionId vxid, ProcSignalReaso extern bool MinimumActiveBackends(int min); extern int CountDBBackends(Oid databaseid); +extern int CountDBConnections(Oid databaseid); extern void CancelDBBackends(Oid databaseid, ProcSignalReason sigmode, bool conflictPending); extern int CountUserBackends(Oid roleid); extern bool CountOtherDBBackends(Oid databaseId,