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Add a function pg_stat_clear_snapshot() that discards any statistics snapshot

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already collected in the current transaction; this allows plpgsql functions to
watch for stats updates even though they are confined to a single transaction.
Use this instead of the previous kluge involving pg_stat_file() to wait for
the stats collector to update in the stats regression test.  Internally,
decouple storage of stats snapshots from transaction boundaries; they'll
now stick around until someone calls pgstat_clear_snapshot --- which xact.c
still does at transaction end, to maintain the previous behavior.  This makes
the logic a lot cleaner, at the price of a couple dozen cycles per transaction
exit.
This commit is contained in:
Tom Lane
2007-02-07 23:11:30 +00:00
parent d9ce68872f
commit aec4cf1c8c
9 changed files with 192 additions and 170 deletions
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154
src/backend/postmaster/pgstat.c
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@ -13,7 +13,7 @@
*
* Copyright (c) 2001-2007, PostgreSQL Global Development Group
*
* $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.144 2007/01/26 20:06:52 tgl Exp $
* $PostgreSQL: pgsql/src/backend/postmaster/pgstat.c,v 1.145 2007/02/07 23:11:29 tgl Exp $
* ----------
*/
#include "postgres.h"
@ -130,9 +130,8 @@ static TabStatArray SharedTabStat = {0, 0, NULL};
static int pgStatXactCommit = 0;
static int pgStatXactRollback = 0;
static TransactionId pgStatDBHashXact = InvalidTransactionId;
static MemoryContext pgStatLocalContext = NULL;
static HTAB *pgStatDBHash = NULL;
static TransactionId pgStatLocalStatusXact = InvalidTransactionId;
static PgBackendStatus *localBackendStatusTable = NULL;
static int localNumBackends = 0;
@ -156,11 +155,13 @@ static void pgstat_beshutdown_hook(int code, Datum arg);
static PgStat_StatDBEntry *pgstat_get_db_entry(Oid databaseid, bool create);
static void pgstat_drop_database(Oid databaseid);
static void pgstat_write_statsfile(void);
static void pgstat_read_statsfile(HTAB **dbhash, Oid onlydb);
static HTAB *pgstat_read_statsfile(Oid onlydb);
static void backend_read_statsfile(void);
static void pgstat_read_current_status(void);
static HTAB *pgstat_collect_oids(Oid catalogid);
static void pgstat_setup_memcxt(void);
static void pgstat_setheader(PgStat_MsgHdr *hdr, StatMsgType mtype);
static void pgstat_send(void *msg, int len);
@ -1535,22 +1536,24 @@ pgstat_report_waiting(bool waiting)
static void
pgstat_read_current_status(void)
{
TransactionId topXid = GetTopTransactionId();
volatile PgBackendStatus *beentry;
PgBackendStatus *localtable;
PgBackendStatus *localentry;
int i;
Assert(!pgStatRunningInCollector);
if (TransactionIdEquals(pgStatLocalStatusXact, topXid))
if (localBackendStatusTable)
return; /* already done */
localBackendStatusTable = (PgBackendStatus *)
MemoryContextAlloc(TopTransactionContext,
pgstat_setup_memcxt();
localtable = (PgBackendStatus *)
MemoryContextAlloc(pgStatLocalContext,
sizeof(PgBackendStatus) * MaxBackends);
localNumBackends = 0;
beentry = BackendStatusArray;
localentry = localBackendStatusTable;
localentry = localtable;
for (i = 1; i <= MaxBackends; i++)
{
/*
@ -1587,7 +1590,8 @@ pgstat_read_current_status(void)
}
}
pgStatLocalStatusXact = topXid;
/* Set the pointer only after completion of a valid table */
localBackendStatusTable = localtable;
}
@ -1720,7 +1724,7 @@ PgstatCollectorMain(int argc, char *argv[])
* zero.
*/
pgStatRunningInCollector = true;
pgstat_read_statsfile(&pgStatDBHash, InvalidOid);
pgStatDBHash = pgstat_read_statsfile(InvalidOid);
/*
* Setup the descriptor set for select(2). Since only one bit in the set
@ -2090,38 +2094,24 @@ pgstat_write_statsfile(void)
* databases' hash table (whose entries point to the tables' hash tables).
* ----------
*/
static void
pgstat_read_statsfile(HTAB **dbhash, Oid onlydb)
static HTAB *
pgstat_read_statsfile(Oid onlydb)
{
PgStat_StatDBEntry *dbentry;
PgStat_StatDBEntry dbbuf;
PgStat_StatTabEntry *tabentry;
PgStat_StatTabEntry tabbuf;
HASHCTL hash_ctl;
HTAB *dbhash;
HTAB *tabhash = NULL;
FILE *fpin;
int32 format_id;
bool found;
MemoryContext use_mcxt;
int mcxt_flags;
/*
* If running in the collector or the autovacuum process, we use the
* DynaHashCxt memory context. If running in a backend, we use the
* TopTransactionContext instead, so the caller must only know the last
* XactId when this call happened to know if his tables are still valid or
* already gone!
* The tables will live in pgStatLocalContext.
*/
if (pgStatRunningInCollector || IsAutoVacuumProcess())
{
use_mcxt = NULL;
mcxt_flags = 0;
}
else
{
use_mcxt = TopTransactionContext;
mcxt_flags = HASH_CONTEXT;
}
pgstat_setup_memcxt();
/*
* Create the DB hashtable
@ -2130,9 +2120,9 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb)
hash_ctl.keysize = sizeof(Oid);
hash_ctl.entrysize = sizeof(PgStat_StatDBEntry);
hash_ctl.hash = oid_hash;
hash_ctl.hcxt = use_mcxt;
*dbhash = hash_create("Databases hash", PGSTAT_DB_HASH_SIZE, &hash_ctl,
HASH_ELEM | HASH_FUNCTION | mcxt_flags);
hash_ctl.hcxt = pgStatLocalContext;
dbhash = hash_create("Databases hash", PGSTAT_DB_HASH_SIZE, &hash_ctl,
HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);
/*
* Try to open the status file. If it doesn't exist, the backends simply
@ -2140,7 +2130,7 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb)
* with empty counters.
*/
if ((fpin = AllocateFile(PGSTAT_STAT_FILENAME, PG_BINARY_R)) == NULL)
return;
return dbhash;
/*
* Verify it's of the expected format.
@ -2178,7 +2168,7 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb)
/*
* Add to the DB hash
*/
dbentry = (PgStat_StatDBEntry *) hash_search(*dbhash,
dbentry = (PgStat_StatDBEntry *) hash_search(dbhash,
(void *) &dbbuf.databaseid,
HASH_ENTER,
&found);
@ -2207,11 +2197,11 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb)
hash_ctl.keysize = sizeof(Oid);
hash_ctl.entrysize = sizeof(PgStat_StatTabEntry);
hash_ctl.hash = oid_hash;
hash_ctl.hcxt = use_mcxt;
hash_ctl.hcxt = pgStatLocalContext;
dbentry->tables = hash_create("Per-database table",
PGSTAT_TAB_HASH_SIZE,
&hash_ctl,
HASH_ELEM | HASH_FUNCTION | mcxt_flags);
HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);
/*
* Arrange that following 'T's add entries to this database's
@ -2274,44 +2264,78 @@ pgstat_read_statsfile(HTAB **dbhash, Oid onlydb)
done:
FreeFile(fpin);
return dbhash;
}
/*
* If not done for this transaction, read the statistics collector
* stats file into some hash tables.
*
* Because we store the tables in TopTransactionContext, the result
* is good for the entire current main transaction.
*
* Inside the autovacuum process, the statfile is assumed to be valid
* "forever", that is one iteration, within one database. This means
* we only consider the statistics as they were when the autovacuum
* iteration started.
* If not already done, read the statistics collector stats file into
* some hash tables. The results will be kept until pgstat_clear_snapshot()
* is called (typically, at end of transaction).
*/
static void
backend_read_statsfile(void)
{
if (IsAutoVacuumProcess())
{
/* already read it? */
if (pgStatDBHash)
return;
Assert(!pgStatRunningInCollector);
pgstat_read_statsfile(&pgStatDBHash, InvalidOid);
}
else
{
TransactionId topXid = GetTopTransactionId();
/* already read it? */
if (pgStatDBHash)
return;
Assert(!pgStatRunningInCollector);
if (!TransactionIdEquals(pgStatDBHashXact, topXid))
{
Assert(!pgStatRunningInCollector);
pgstat_read_statsfile(&pgStatDBHash, MyDatabaseId);
pgStatDBHashXact = topXid;
}
}
/* Autovacuum wants stats about all databases */
if (IsAutoVacuumProcess())
pgStatDBHash = pgstat_read_statsfile(InvalidOid);
else
pgStatDBHash = pgstat_read_statsfile(MyDatabaseId);
}
/* ----------
* pgstat_setup_memcxt() -
*
* Create pgStatLocalContext, if not already done.
* ----------
*/
static void
pgstat_setup_memcxt(void)
{
if (!pgStatLocalContext)
pgStatLocalContext = AllocSetContextCreate(TopMemoryContext,
"Statistics snapshot",
ALLOCSET_SMALL_MINSIZE,
ALLOCSET_SMALL_INITSIZE,
ALLOCSET_SMALL_MAXSIZE);
}
/* ----------
* pgstat_clear_snapshot() -
*
* Discard any data collected in the current transaction. Any subsequent
* request will cause new snapshots to be read.
*
* This is also invoked during transaction commit or abort to discard
* the no-longer-wanted snapshot.
* ----------
*/
void
pgstat_clear_snapshot(void)
{
/* In an autovacuum process we keep the stats forever */
if (IsAutoVacuumProcess())
return;
/* Release memory, if any was allocated */
if (pgStatLocalContext)
MemoryContextDelete(pgStatLocalContext);
/* Reset variables */
pgStatLocalContext = NULL;
pgStatDBHash = NULL;
localBackendStatusTable = NULL;
localNumBackends = 0;
}
/* ----------
* pgstat_recv_tabstat() -
*