*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.73 2008/01/01 19:45:48 momjian Exp $
+ * $PostgreSQL: pgsql/src/backend/access/transam/transam.c,v 1.74 2008/03/11 20:20:35 tgl Exp $
*
* NOTES
* This file contains the high level access-method interface to the
#include "utils/tqual.h"
-static XidStatus TransactionLogFetch(TransactionId transactionId);
-static void TransactionLogUpdate(TransactionId transactionId,
- XidStatus status, XLogRecPtr lsn);
-
/*
- * Single-item cache for results of TransactionLogFetch.
+ * Single-item cache for results of TransactionLogFetch. It's worth having
+ * such a cache because we frequently find ourselves repeatedly checking the
+ * same XID, for example when scanning a table just after a bulk insert,
+ * update, or delete.
*/
static TransactionId cachedFetchXid = InvalidTransactionId;
static XidStatus cachedFetchXidStatus;
/* Handy constant for an invalid xlog recptr */
static const XLogRecPtr InvalidXLogRecPtr = {0, 0};
+/* Local functions */
+static XidStatus TransactionLogFetch(TransactionId transactionId);
+static void TransactionLogUpdate(TransactionId transactionId,
+ XidStatus status, XLogRecPtr lsn);
+
/* ----------------------------------------------------------------
- * postgres log access method interface
+ * Postgres log access method interface
*
* TransactionLogFetch
* TransactionLogUpdate
xidstatus = TransactionIdGetStatus(transactionId, &xidlsn);
/*
- * DO NOT cache status for unfinished or sub-committed transactions! We
- * only cache status that is guaranteed not to change.
+ * Cache it, but DO NOT cache status for unfinished or sub-committed
+ * transactions! We only cache status that is guaranteed not to change.
*/
if (xidstatus != TRANSACTION_STATUS_IN_PROGRESS &&
xidstatus != TRANSACTION_STATUS_SUB_COMMITTED)
return xidstatus;
}
-/* --------------------------------
+/*
* TransactionLogUpdate
*
* Store the new status of a transaction. The commit record LSN must be
* passed when recording an async commit; else it should be InvalidXLogRecPtr.
- * --------------------------------
*/
static inline void
TransactionLogUpdate(TransactionId transactionId,
TransactionIdSetStatus(xids[i], status, lsn);
}
+
/* ----------------------------------------------------------------
* Interface functions
*
- * TransactionId DidCommit
- * TransactionId DidAbort
- * TransactionId IsInProgress
+ * TransactionIdDidCommit
+ * TransactionIdDidAbort
* ========
* these functions test the transaction status of
* a specified transaction id.
*
- * TransactionId Commit
- * TransactionId Abort
+ * TransactionIdCommit
+ * TransactionIdAbort
* ========
* these functions set the transaction status
* of the specified xid.
*
+ * See also TransactionIdIsInProgress, which once was in this module
+ * but now lives in procarray.c.
* ----------------------------------------------------------------
*/
-/* --------------------------------
- * TransactionId DidCommit
- * TransactionId DidAbort
- * TransactionId IsInProgress
- * --------------------------------
- */
-
/*
* TransactionIdDidCommit
* True iff transaction associated with the identifier did commit.
return false;
}
-/* --------------------------------
- * TransactionId Commit
- * TransactionId Abort
- * --------------------------------
+/*
+ * TransactionIdIsKnownCompleted
+ * True iff transaction associated with the identifier is currently
+ * known to have either committed or aborted.
+ *
+ * This does NOT look into pg_clog but merely probes our local cache
+ * (and so it's not named TransactionIdDidComplete, which would be the
+ * appropriate name for a function that worked that way). The intended
+ * use is just to short-circuit TransactionIdIsInProgress calls when doing
+ * repeated tqual.c checks for the same XID. If this isn't extremely fast
+ * then it will be counterproductive.
+ *
+ * Note:
+ * Assumes transaction identifier is valid.
*/
+bool
+TransactionIdIsKnownCompleted(TransactionId transactionId)
+{
+ if (TransactionIdEquals(transactionId, cachedFetchXid))
+ {
+ /* If it's in the cache at all, it must be completed. */
+ return true;
+ }
+
+ return false;
+}
+
/*
* TransactionIdCommit
TransactionLogUpdate(transactionId, TRANSACTION_STATUS_COMMITTED, lsn);
}
-
/*
* TransactionIdAbort
* Aborts the transaction associated with the identifier.
lsn);
}
-
/*
* TransactionIdAbortTree
* Marks all the given transaction ids as aborted.
InvalidXLogRecPtr);
}
+
/*
* TransactionIdPrecedes --- is id1 logically < id2?
*/
*
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.40 2008/01/09 21:52:36 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/storage/ipc/procarray.c,v 1.41 2008/03/11 20:20:35 tgl Exp $
*
*-------------------------------------------------------------------------
*/
/* counters for XidCache measurement */
static long xc_by_recent_xmin = 0;
+static long xc_by_known_xact = 0;
static long xc_by_my_xact = 0;
static long xc_by_latest_xid = 0;
static long xc_by_main_xid = 0;
static long xc_slow_answer = 0;
#define xc_by_recent_xmin_inc() (xc_by_recent_xmin++)
+#define xc_by_known_xact_inc() (xc_by_known_xact++)
#define xc_by_my_xact_inc() (xc_by_my_xact++)
#define xc_by_latest_xid_inc() (xc_by_latest_xid++)
#define xc_by_main_xid_inc() (xc_by_main_xid++)
#else /* !XIDCACHE_DEBUG */
#define xc_by_recent_xmin_inc() ((void) 0)
+#define xc_by_known_xact_inc() ((void) 0)
#define xc_by_my_xact_inc() ((void) 0)
#define xc_by_latest_xid_inc() ((void) 0)
#define xc_by_main_xid_inc() ((void) 0)
return false;
}
+ /*
+ * We may have just checked the status of this transaction, so if it is
+ * already known to be completed, we can fall out without any access to
+ * shared memory.
+ */
+ if (TransactionIdIsKnownCompleted(xid))
+ {
+ xc_by_known_xact_inc();
+ return false;
+ }
+
/*
* Also, we can handle our own transaction (and subtransactions) without
* any access to shared memory.
DisplayXidCache(void)
{
fprintf(stderr,
- "XidCache: xmin: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, nooflo: %ld, slow: %ld\n",
+ "XidCache: xmin: %ld, known: %ld, myxact: %ld, latest: %ld, mainxid: %ld, childxid: %ld, nooflo: %ld, slow: %ld\n",
xc_by_recent_xmin,
+ xc_by_known_xact,
xc_by_my_xact,
xc_by_latest_xid,
xc_by_main_xid,
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