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Finish up the flat-files project: get rid of GetRawDatabaseInfo() hack
in favor of looking at the flat file copy of pg_database during backend startup. This should finally eliminate the various corner cases in which backend startup fails unexpectedly because it isn't able to distinguish live and dead tuples in pg_database. Simplify locking on pg_database to be similar to the rules used with pg_shadow and pg_group, and eliminate FlushRelationBuffers operations that were used only to reduce the odds of failure of GetRawDatabaseInfo. initdb forced due to addition of a trigger to pg_database.
This commit is contained in:
Tom Lane
@ -3,13 +3,19 @@
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* dbcommands.c
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* Database management commands (create/drop database).
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*
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* Note: database creation/destruction commands take ExclusiveLock on
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* pg_database to ensure that no two proceed in parallel. We must use
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* at least this level of locking to ensure that no two backends try to
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* write the flat-file copy of pg_database at once. We avoid using
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* AccessExclusiveLock since there's no need to lock out ordinary readers
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* of pg_database.
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*
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* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.150 2005/02/20 02:21:34 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/commands/dbcommands.c,v 1.151 2005/02/26 18:43:33 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -446,13 +452,13 @@ createdb(const CreatedbStmt *stmt)
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/*
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* Now OK to grab exclusive lock on pg_database.
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*/
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pg_database_rel = heap_openr(DatabaseRelationName, AccessExclusiveLock);
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pg_database_rel = heap_openr(DatabaseRelationName, ExclusiveLock);
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/* Check to see if someone else created same DB name meanwhile. */
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if (get_db_info(dbname, NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL))
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{
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/* Don't hold lock while doing recursive remove */
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heap_close(pg_database_rel, AccessExclusiveLock);
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heap_close(pg_database_rel, ExclusiveLock);
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remove_dbtablespaces(dboid);
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ereport(ERROR,
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(errcode(ERRCODE_DUPLICATE_DATABASE),
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@ -498,13 +504,6 @@ createdb(const CreatedbStmt *stmt)
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/* Update indexes */
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CatalogUpdateIndexes(pg_database_rel, tuple);
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/*
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* Force dirty buffers out to disk, so that newly-connecting backends
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* will see the new database in pg_database right away. (They'll see
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* an uncommitted tuple, but they don't care; see GetRawDatabaseInfo.)
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*/
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FlushRelationBuffers(pg_database_rel, MaxBlockNumber);
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/* Close pg_database, but keep exclusive lock till commit */
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heap_close(pg_database_rel, NoLock);
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@ -542,12 +541,15 @@ dropdb(const char *dbname)
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* Obtain exclusive lock on pg_database. We need this to ensure that
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* no new backend starts up in the target database while we are
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* deleting it. (Actually, a new backend might still manage to start
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* up, because it will read pg_database without any locking to
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* discover the database's OID. But it will detect its error in
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* ReverifyMyDatabase and shut down before any serious damage is done.
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* See postinit.c.)
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* up, because it isn't able to lock pg_database while starting. But
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* it will detect its error in ReverifyMyDatabase and shut down before
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* any serious damage is done. See postinit.c.)
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*
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* An ExclusiveLock, rather than AccessExclusiveLock, is sufficient
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* since ReverifyMyDatabase takes RowShareLock. This allows ordinary
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* readers of pg_database to proceed in parallel.
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*/
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pgdbrel = heap_openr(DatabaseRelationName, AccessExclusiveLock);
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pgdbrel = heap_openr(DatabaseRelationName, ExclusiveLock);
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if (!get_db_info(dbname, &db_id, &db_owner, NULL,
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&db_istemplate, NULL, NULL, NULL, NULL))
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@ -638,14 +640,6 @@ dropdb(const char *dbname)
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*/
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remove_dbtablespaces(db_id);
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/*
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* Force dirty buffers out to disk, so that newly-connecting backends
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* will see the database tuple marked dead in pg_database right away.
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* (They'll see an uncommitted deletion, but they don't care; see
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* GetRawDatabaseInfo.)
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*/
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FlushRelationBuffers(pgdbrel, MaxBlockNumber);
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/* Close pg_database, but keep exclusive lock till commit */
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heap_close(pgdbrel, NoLock);
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@ -671,10 +665,10 @@ RenameDatabase(const char *oldname, const char *newname)
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key2;
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/*
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* Obtain AccessExclusiveLock so that no new session gets started
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* Obtain ExclusiveLock so that no new session gets started
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* while the rename is in progress.
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*/
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rel = heap_openr(DatabaseRelationName, AccessExclusiveLock);
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rel = heap_openr(DatabaseRelationName, ExclusiveLock);
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ScanKeyInit(&key,
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Anum_pg_database_datname,
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@ -742,14 +736,6 @@ RenameDatabase(const char *oldname, const char *newname)
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systable_endscan(scan);
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/*
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* Force dirty buffers out to disk, so that newly-connecting backends
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* will see the renamed database in pg_database right away. (They'll
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* see an uncommitted tuple, but they don't care; see
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* GetRawDatabaseInfo.)
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*/
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FlushRelationBuffers(rel, MaxBlockNumber);
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/* Close pg_database, but keep exclusive lock till commit */
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heap_close(rel, NoLock);
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@ -779,9 +765,10 @@ AlterDatabaseSet(AlterDatabaseSetStmt *stmt)
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valuestr = flatten_set_variable_args(stmt->variable, stmt->value);
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/*
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* We need AccessExclusiveLock so we can safely do FlushRelationBuffers.
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* We don't need ExclusiveLock since we aren't updating the
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* flat file.
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*/
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rel = heap_openr(DatabaseRelationName, AccessExclusiveLock);
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rel = heap_openr(DatabaseRelationName, RowExclusiveLock);
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ScanKeyInit(&scankey,
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Anum_pg_database_datname,
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BTEqualStrategyNumber, F_NAMEEQ,
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@ -840,15 +827,7 @@ AlterDatabaseSet(AlterDatabaseSetStmt *stmt)
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systable_endscan(scan);
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/*
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* Force dirty buffers out to disk, so that newly-connecting backends
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* will see the altered row in pg_database right away. (They'll
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* see an uncommitted tuple, but they don't care; see
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* GetRawDatabaseInfo.)
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*/
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FlushRelationBuffers(rel, MaxBlockNumber);
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/* Close pg_database, but keep exclusive lock till commit */
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/* Close pg_database, but keep lock till commit */
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heap_close(rel, NoLock);
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/*
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@ -871,9 +850,10 @@ AlterDatabaseOwner(const char *dbname, AclId newOwnerSysId)
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Form_pg_database datForm;
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/*
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* We need AccessExclusiveLock so we can safely do FlushRelationBuffers.
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* We don't need ExclusiveLock since we aren't updating the
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* flat file.
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*/
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rel = heap_openr(DatabaseRelationName, AccessExclusiveLock);
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rel = heap_openr(DatabaseRelationName, RowExclusiveLock);
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ScanKeyInit(&scankey,
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Anum_pg_database_datname,
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BTEqualStrategyNumber, F_NAMEEQ,
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@ -937,22 +917,11 @@ AlterDatabaseOwner(const char *dbname, AclId newOwnerSysId)
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CatalogUpdateIndexes(rel, newtuple);
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heap_freetuple(newtuple);
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/* must release buffer pins before FlushRelationBuffers */
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systable_endscan(scan);
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/*
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* Force dirty buffers out to disk, so that newly-connecting backends
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* will see the altered row in pg_database right away. (They'll
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* see an uncommitted tuple, but they don't care; see
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* GetRawDatabaseInfo.)
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*/
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FlushRelationBuffers(rel, MaxBlockNumber);
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}
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else
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systable_endscan(scan);
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/* Close pg_database, but keep exclusive lock till commit */
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systable_endscan(scan);
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/* Close pg_database, but keep lock till commit */
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heap_close(rel, NoLock);
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/*
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