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Implement rate-limiting logic on how often backends will attempt to send

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messages to the stats collector.  This avoids the problem that enabling
stats_row_level for autovacuum has a significant overhead for short
read-only transactions, as noted by Arjen van der Meijden.  We can avoid
an extra gettimeofday call by piggybacking on the one done for WAL-logging
xact commit or abort (although that doesn't help read-only transactions,
since they don't WAL-log anything).

In my proposal for this, I noted that we could change the WAL log entries
for commit/abort to record full TimestampTz precision, instead of only
time_t as at present.  That's not done in this patch, but will be committed
separately.
This commit is contained in:
Tom Lane
2007-04-30 03:23:49 +00:00
parent 57b82bf324
commit 957d08c81f
9 changed files with 104 additions and 47 deletions
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37
src/backend/access/transam/xact.c
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@@ -10,7 +10,7 @@
*
*
* IDENTIFICATION
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.240 2007/04/26 23:24:44 tgl Exp $
* $PostgreSQL: pgsql/src/backend/access/transam/xact.c,v 1.241 2007/04/30 03:23:48 tgl Exp $
*
*-------------------------------------------------------------------------
*/
@@ -160,11 +160,13 @@ static CommandId currentCommandId;
/*
* xactStartTimestamp is the value of transaction_timestamp().
* stmtStartTimestamp is the value of statement_timestamp().
* xactStopTimestamp is the time at which we log a commit or abort WAL record.
* These do not change as we enter and exit subtransactions, so we don't
* keep them inside the TransactionState stack.
*/
static TimestampTz xactStartTimestamp;
static TimestampTz stmtStartTimestamp;
static TimestampTz xactStopTimestamp;
/*
* GID to be used for preparing the current transaction. This is also
@@ -435,6 +437,20 @@ GetCurrentStatementStartTimestamp(void)
return stmtStartTimestamp;
}
/*
* GetCurrentTransactionStopTimestamp
*
* We return current time if the transaction stop time hasn't been set
* (which can happen if we decide we don't need to log an XLOG record).
*/
TimestampTz
GetCurrentTransactionStopTimestamp(void)
{
if (xactStopTimestamp != 0)
return xactStopTimestamp;
return GetCurrentTimestamp();
}
/*
* SetCurrentStatementStartTimestamp
*/
@@ -444,6 +460,15 @@ SetCurrentStatementStartTimestamp(void)
stmtStartTimestamp = GetCurrentTimestamp();
}
/*
* SetCurrentTransactionStopTimestamp
*/
static inline void
SetCurrentTransactionStopTimestamp(void)
{
xactStopTimestamp = GetCurrentTimestamp();
}
/*
* GetCurrentTransactionNestLevel
*
@@ -747,7 +772,8 @@ RecordTransactionCommit(void)
*/
MyProc->inCommit = true;
xlrec.xtime = time(NULL);
SetCurrentTransactionStopTimestamp();
xlrec.xtime = timestamptz_to_time_t(xactStopTimestamp);
xlrec.nrels = nrels;
xlrec.nsubxacts = nchildren;
rdata[0].data = (char *) (&xlrec);
@@ -1042,7 +1068,8 @@ RecordTransactionAbort(void)
xl_xact_abort xlrec;
XLogRecPtr recptr;
xlrec.xtime = time(NULL);
SetCurrentTransactionStopTimestamp();
xlrec.xtime = timestamptz_to_time_t(xactStopTimestamp);
xlrec.nrels = nrels;
xlrec.nsubxacts = nchildren;
rdata[0].data = (char *) (&xlrec);
@@ -1415,9 +1442,11 @@ StartTransaction(void)
/*
* set transaction_timestamp() (a/k/a now()). We want this to be the same
* as the first command's statement_timestamp(), so don't do a fresh
* GetCurrentTimestamp() call (which'd be expensive anyway).
* GetCurrentTimestamp() call (which'd be expensive anyway). Also,
* mark xactStopTimestamp as unset.
*/
xactStartTimestamp = stmtStartTimestamp;
xactStopTimestamp = 0;
pgstat_report_txn_timestamp(xactStartTimestamp);
/*