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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
@ -8,7 +8,7 @@
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*
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*
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* IDENTIFICATION
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* $PostgreSQL: pgsql/src/backend/utils/init/postinit.c,v 1.140 2005/02/20 21:46:49 tgl Exp $
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* $PostgreSQL: pgsql/src/backend/utils/init/postinit.c,v 1.141 2005/02/26 18:43:33 tgl Exp $
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*
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*
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*-------------------------------------------------------------------------
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@ -27,14 +27,16 @@
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#include "catalog/pg_database.h"
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#include "catalog/pg_shadow.h"
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#include "catalog/pg_tablespace.h"
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#include "libpq/hba.h"
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#include "mb/pg_wchar.h"
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#include "miscadmin.h"
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#include "postmaster/postmaster.h"
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#include "storage/backendid.h"
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#include "storage/fd.h"
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#include "storage/ipc.h"
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#include "storage/proc.h"
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#include "storage/sinval.h"
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#include "storage/smgr.h"
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#include "utils/flatfiles.h"
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#include "utils/fmgroids.h"
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#include "utils/guc.h"
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#include "utils/portal.h"
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@ -42,6 +44,7 @@
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#include "utils/syscache.h"
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static bool FindMyDatabase(const char *name, Oid *db_id, Oid *db_tablespace);
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static void ReverifyMyDatabase(const char *name);
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static void InitCommunication(void);
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static void ShutdownPostgres(int code, Datum arg);
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@ -51,18 +54,60 @@ static bool ThereIsAtLeastOneUser(void);
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/*** InitPostgres support ***/
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/* --------------------------------
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* ReverifyMyDatabase
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/*
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* FindMyDatabase -- get the critical info needed to locate my database
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*
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* Since we are forced to fetch the database OID out of pg_database without
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* benefit of locking or transaction ID checking (see utils/misc/database.c),
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* we might have gotten a wrong answer. Or, we might have attached to a
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* database that's in process of being destroyed by destroydb(). This
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* routine is called after we have all the locking and other infrastructure
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* running --- now we can check that we are really attached to a valid
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* database.
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* Find the named database in pg_database, return its database OID and the
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* OID of its default tablespace. Return TRUE if found, FALSE if not.
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*
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* In reality, if destroydb() is running in parallel with our startup,
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* Since we are not yet up and running as a backend, we cannot look directly
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* at pg_database (we can't obtain locks nor participate in transactions).
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* So to get the info we need before starting up, we must look at the "flat
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* file" copy of pg_database that is helpfully maintained by flatfiles.c.
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* This is subject to various race conditions, so after we have the
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* transaction infrastructure started, we have to recheck the information;
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* see ReverifyMyDatabase.
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*/
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static bool
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FindMyDatabase(const char *name, Oid *db_id, Oid *db_tablespace)
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{
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bool result = false;
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char *filename;
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FILE *db_file;
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char thisname[NAMEDATALEN];
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filename = database_getflatfilename();
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db_file = AllocateFile(filename, "r");
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if (db_file == NULL)
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ereport(FATAL,
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(errcode_for_file_access(),
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errmsg("could not open file \"%s\": %m", filename)));
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while (read_pg_database_line(db_file, thisname, db_id, db_tablespace))
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{
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if (strcmp(thisname, name) == 0)
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{
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result = true;
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break;
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}
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}
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FreeFile(db_file);
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pfree(filename);
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return result;
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}
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/*
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* ReverifyMyDatabase -- recheck info obtained by FindMyDatabase
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*
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* Since FindMyDatabase cannot lock pg_database, the information it read
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* could be stale; for example we might have attached to a database that's in
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* process of being destroyed by dropdb(). This routine is called after
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* we have all the locking and other infrastructure running --- now we can
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* check that we are really attached to a valid database.
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*
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* In reality, if dropdb() is running in parallel with our startup,
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* it's pretty likely that we will have failed before now, due to being
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* unable to read some of the system tables within the doomed database.
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* This routine just exists to make *sure* we have not started up in an
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@ -75,7 +120,6 @@ static bool ThereIsAtLeastOneUser(void);
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* To avoid having to read pg_database more times than necessary
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* during session startup, this place is also fitting to set up any
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* database-specific configuration variables.
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* --------------------------------
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*/
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static void
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ReverifyMyDatabase(const char *name)
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@ -87,10 +131,10 @@ ReverifyMyDatabase(const char *name)
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Form_pg_database dbform;
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/*
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* Because we grab AccessShareLock here, we can be sure that destroydb
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* Because we grab RowShareLock here, we can be sure that dropdb()
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* is not running in parallel with us (any more).
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*/
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pgdbrel = heap_openr(DatabaseRelationName, AccessShareLock);
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pgdbrel = heap_openr(DatabaseRelationName, RowShareLock);
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ScanKeyInit(&key,
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Anum_pg_database_datname,
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@ -104,7 +148,7 @@ ReverifyMyDatabase(const char *name)
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HeapTupleGetOid(tup) != MyDatabaseId)
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{
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/* OOPS */
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heap_close(pgdbrel, AccessShareLock);
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heap_close(pgdbrel, RowShareLock);
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/*
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* The only real problem I could have created is to load dirty
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@ -131,7 +175,7 @@ ReverifyMyDatabase(const char *name)
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name)));
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/*
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* OK, we're golden. Only other to-do item is to save the encoding
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* OK, we're golden. Next to-do item is to save the encoding
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* info out of the pg_database tuple.
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*/
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SetDatabaseEncoding(dbform->encoding);
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@ -143,7 +187,7 @@ ReverifyMyDatabase(const char *name)
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PGC_BACKEND, PGC_S_DEFAULT);
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/*
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* Set up database-specific configuration variables.
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* Lastly, set up any database-specific configuration variables.
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*/
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if (IsUnderPostmaster)
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{
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@ -161,7 +205,7 @@ ReverifyMyDatabase(const char *name)
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}
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heap_endscan(pgdbscan);
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heap_close(pgdbrel, AccessShareLock);
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heap_close(pgdbrel, RowShareLock);
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}
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@ -261,11 +305,9 @@ InitPostgres(const char *dbname, const char *username)
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/*
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* Find oid and tablespace of the database we're about to open.
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* Since we're not yet up and running we have to use the hackish
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* GetRawDatabaseInfo.
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* FindMyDatabase.
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*/
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GetRawDatabaseInfo(dbname, &MyDatabaseId, &MyDatabaseTableSpace);
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if (!OidIsValid(MyDatabaseId))
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if (!FindMyDatabase(dbname, &MyDatabaseId, &MyDatabaseTableSpace))
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ereport(FATAL,
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(errcode(ERRCODE_UNDEFINED_DATABASE),
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errmsg("database \"%s\" does not exist",
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