From 5541abee0dd56669ef0e9a87121e449d905c3efd Mon Sep 17 00:00:00 2001
From: "Vadim B. Mikheev" <vadim4o@yahoo.com>
Date: Thu, 3 Jun 1999 13:33:13 +0000
Subject: [PATCH] 1. Additional fix against ERROR: Child itemid marked as
unused in CommitTransaction(). 2. Changes in GetSnapshotData().
---
src/backend/access/transam/xact.c | 36 ++++++++++++++++++-----------
src/backend/storage/ipc/shmem.c | 38 +++++++++++++++++++++----------
2 files changed, 49 insertions(+), 25 deletions(-)
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index 6884e635904..6bde05733ac 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.38 1999/06/03 04:41:41 vadim Exp $
+ * $Header: /cvsroot/pgsql/src/backend/access/transam/xact.c,v 1.39 1999/06/03 13:33:12 vadim Exp $
*
* NOTES
* Transaction aborts can now occur two ways:
@@ -646,18 +646,6 @@ RecordTransactionCommit()
FlushBufferPool(!TransactionFlushEnabled());
if (leak)
ResetBufferPool();
-
- /*
- * Let others know about no transaction in progress.
- * Note that this must be done _before_ releasing locks
- * we hold or bad (too high) XmaxRecent value might be
- * used by vacuum.
- */
- if (MyProc != (PROC *) NULL)
- {
- MyProc->xid = InvalidTransactionId;
- MyProc->xmin = InvalidTransactionId;
- }
}
@@ -950,6 +938,28 @@ CommitTransaction()
DestroyNoNameRels();
AtEOXact_portals();
RecordTransactionCommit();
+
+ /*
+ * Let others know about no transaction in progress by me.
+ * Note that this must be done _before_ releasing locks we hold
+ * and SpinAcquire(ShmemIndexLock) is required - or bad (too high)
+ * XmaxRecent value might be used by vacuum: UPDATE with xid 0 is
+ * blocked by xid 1' UPDATE, xid 1 is doing commit while xid 2
+ * gets snapshot - if xid 2' GetSnapshotData sees xid 1 as running
+ * then it must see xid 0 as running as well or XmaxRecent = 1
+ * might be used by concurrent vacuum causing
+ * ERROR: Child itemid marked as unused
+ * This bug was reported by Hiroshi Inoue and I was able to reproduce
+ * it with 3 sessions and gdb. - vadim 06/03/99
+ */
+ if (MyProc != (PROC *) NULL)
+ {
+ SpinAcquire(ShmemIndexLock);
+ MyProc->xid = InvalidTransactionId;
+ MyProc->xmin = InvalidTransactionId;
+ SpinRelease(ShmemIndexLock);
+ }
+
RelationPurgeLocalRelation(true);
AtCommit_Cache();
AtCommit_Locks();
diff --git a/src/backend/storage/ipc/shmem.c b/src/backend/storage/ipc/shmem.c
index eafe53b0bb1..04cfa1a812e 100644
--- a/src/backend/storage/ipc/shmem.c
+++ b/src/backend/storage/ipc/shmem.c
@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
- * $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.40 1999/05/25 16:11:11 momjian Exp $
+ * $Header: /cvsroot/pgsql/src/backend/storage/ipc/shmem.c,v 1.41 1999/06/03 13:33:13 vadim Exp $
*
*-------------------------------------------------------------------------
*/
@@ -593,6 +593,10 @@ ShmemInitStruct(char *name, unsigned long size, bool *foundPtr)
*
* Strange place for this func, but we have to lookup process data structures
* for all running backends. - vadim 11/26/96
+ *
+ * We should keep all PROC structs not in ShmemIndex - this is too
+ * general hash table...
+ *
*/
bool
TransactionIdIsInProgress(TransactionId xid)
@@ -648,10 +652,7 @@ GetSnapshotData(bool serializable)
snapshot->xip = (TransactionId *) malloc(have * sizeof(TransactionId));
snapshot->xmin = cid;
- if (serializable)
- snapshot->xmax = cid;
- else
- ReadNewTransactionId(&(snapshot->xmax));
+ ReadNewTransactionId(&(snapshot->xmax));
SpinAcquire(ShmemIndexLock);
@@ -660,8 +661,10 @@ GetSnapshotData(bool serializable)
{
if (result == (ShmemIndexEnt *) TRUE)
{
- if (MyProc->xmin == InvalidTransactionId)
+ if (serializable)
MyProc->xmin = snapshot->xmin;
+ /* Serializable snapshot must be computed before any other... */
+ Assert(MyProc->xmin != InvalidTransactionId);
SpinRelease(ShmemIndexLock);
snapshot->xcnt = count;
return snapshot;
@@ -670,13 +673,24 @@ GetSnapshotData(bool serializable)
strncmp(result->key, "PID ", 4) != 0)
continue;
proc = (PROC *) MAKE_PTR(result->location);
- xid = proc->xid; /* we don't use spin-locking in xact.c ! */
- if (proc == MyProc || xid < FirstTransactionId)
+ /*
+ * We don't use spin-locking when changing proc->xid
+ * in GetNewTransactionId() and in AbortTransaction() !..
+ */
+ xid = proc->xid;
+ if (proc == MyProc ||
+ xid < FirstTransactionId || xid >= snapshot->xmax)
+ {
+ /*
+ * Seems that there is no sense to store xid >= snapshot->xmax
+ * (what we got from ReadNewTransactionId above) in snapshot->xip
+ * - we just assume that all xacts with such xid-s are running
+ * and may be ignored.
+ */
continue;
+ }
if (xid < snapshot->xmin)
snapshot->xmin = xid;
- else if (xid > snapshot->xmax)
- snapshot->xmax = xid;
if (have == 0)
{
snapshot->xip = (TransactionId *) realloc(snapshot->xip,
@@ -712,7 +726,7 @@ GetXmaxRecent(TransactionId *XmaxRecent)
Assert(ShmemIndex);
- ReadNewTransactionId(XmaxRecent);
+ *XmaxRecent = GetCurrentTransactionId();
SpinAcquire(ShmemIndexLock);
@@ -728,7 +742,7 @@ GetXmaxRecent(TransactionId *XmaxRecent)
strncmp(result->key, "PID ", 4) != 0)
continue;
proc = (PROC *) MAKE_PTR(result->location);
- xmin = proc->xmin; /* we don't use spin-locking in xact.c ! */
+ xmin = proc->xmin; /* we don't use spin-locking in AbortTransaction() ! */
if (proc == MyProc || xmin < FirstTransactionId)
continue;
if (xmin < *XmaxRecent)
--
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