database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-11 10:01:57 +03:00
Code Activity

Prevent "snapshot too old" from trying to return pruned TOAST tuples.

Browse Source 
Previously, we tested for MVCC snapshots to see whether they were too
old, but not TOAST snapshots, which can lead to complaints about missing
TOAST chunks if those chunks are subject to early pruning.  Ideally,
the threshold lsn and timestamp for a TOAST snapshot would be that of
the corresponding MVCC snapshot, but since we have no way of deciding
which MVCC snapshot was used to fetch the TOAST pointer, use the oldest
active or registered snapshot instead.

Reported by Andres Freund, who also sketched out what the fix should
look like.  Patch by me, reviewed by Amit Kapila.
This commit is contained in:
Robert Haas
2016-08-03 16:41:43 -04:00
parent a3c7a993d5
commit 3e2f3c2e42
6 changed files with 96 additions and 16 deletions
Download Patch File Download Diff File Expand all files Collapse all files

38
src/backend/utils/time/snapmgr.c
View File

@ -188,6 +188,9 @@ typedef struct ActiveSnapshotElt
/* Top of the stack of active snapshots */
static ActiveSnapshotElt *ActiveSnapshot = NULL;
/* Bottom of the stack of active snapshots */
static ActiveSnapshotElt *OldestActiveSnapshot = NULL;
/*
* Currently registered Snapshots. Ordered in a heap by xmin, so that we can
* quickly find the one with lowest xmin, to advance our MyPgXat->xmin.
@ -393,6 +396,34 @@ GetLatestSnapshot(void)
return SecondarySnapshot;
}
/*
* GetOldestSnapshot
*
* Get the oldest known snapshot, as judged by the LSN.
*/
Snapshot
GetOldestSnapshot(void)
{
Snapshot OldestRegisteredSnapshot = NULL;
XLogRecPtr RegisteredLSN = InvalidXLogRecPtr;
XLogRecPtr ActiveLSN = InvalidXLogRecPtr;
if (!pairingheap_is_empty(&RegisteredSnapshots))
{
OldestRegisteredSnapshot = pairingheap_container(SnapshotData, ph_node,
pairingheap_first(&RegisteredSnapshots));
RegisteredLSN = OldestRegisteredSnapshot->lsn;
}
if (OldestActiveSnapshot != NULL)
ActiveLSN = OldestActiveSnapshot->as_snap->lsn;
if (XLogRecPtrIsInvalid(RegisteredLSN) || RegisteredLSN > ActiveLSN)
return OldestActiveSnapshot->as_snap;
return OldestRegisteredSnapshot;
}
/*
* GetCatalogSnapshot
* Get a snapshot that is sufficiently up-to-date for scan of the
@ -674,6 +705,8 @@ PushActiveSnapshot(Snapshot snap)
newactive->as_snap->active_count++;
ActiveSnapshot = newactive;
if (OldestActiveSnapshot == NULL)
OldestActiveSnapshot = ActiveSnapshot;
}
/*
@ -744,6 +777,8 @@ PopActiveSnapshot(void)
pfree(ActiveSnapshot);
ActiveSnapshot = newstack;
if (ActiveSnapshot == NULL)
OldestActiveSnapshot = NULL;
SnapshotResetXmin();
}
@ -953,6 +988,8 @@ AtSubAbort_Snapshot(int level)
pfree(ActiveSnapshot);
ActiveSnapshot = next;
if (ActiveSnapshot == NULL)
OldestActiveSnapshot = NULL;
}
SnapshotResetXmin();
@ -1037,6 +1074,7 @@ AtEOXact_Snapshot(bool isCommit)
* it'll go away with TopTransactionContext.
*/
ActiveSnapshot = NULL;
OldestActiveSnapshot = NULL;
pairingheap_reset(&RegisteredSnapshots);
CurrentSnapshot = NULL;