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Add the "snapshot too old" feature

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This feature is controlled by a new old_snapshot_threshold GUC.  A
value of -1 disables the feature, and that is the default.  The
value of 0 is just intended for testing.  Above that it is the
number of minutes a snapshot can reach before pruning and vacuum
are allowed to remove dead tuples which the snapshot would
otherwise protect.  The xmin associated with a transaction ID does
still protect dead tuples.  A connection which is using an "old"
snapshot does not get an error unless it accesses a page modified
recently enough that it might not be able to produce accurate
results.

This is similar to the Oracle feature, and we use the same SQLSTATE
and error message for compatibility.
This commit is contained in:
Kevin Grittner
2016-04-08 14:36:30 -05:00
parent 8b65cf4c5e
commit 848ef42bb8
41 changed files with 942 additions and 85 deletions
Download Patch File Download Diff File Expand all files Collapse all files

31
src/backend/access/heap/heapam.c
View File

@ -394,7 +394,8 @@ heapgetpage(HeapScanDesc scan, BlockNumber page)
*/
LockBuffer(buffer, BUFFER_LOCK_SHARE);
dp = BufferGetPage(buffer, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(buffer, snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lines = PageGetMaxOffsetNumber(dp);
ntup = 0;
@ -537,7 +538,7 @@ heapgettup(HeapScanDesc scan,
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, snapshot, scan->rs_rd, BGP_TEST_FOR_OLD_SNAPSHOT);
lines = PageGetMaxOffsetNumber(dp);
/* page and lineoff now reference the physically next tid */
@ -582,7 +583,8 @@ heapgettup(HeapScanDesc scan,
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lines = PageGetMaxOffsetNumber(dp);
if (!scan->rs_inited)
@ -616,7 +618,8 @@ heapgettup(HeapScanDesc scan,
heapgetpage(scan, page);
/* Since the tuple was previously fetched, needn't lock page here */
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
lpp = PageGetItemId(dp, lineoff);
Assert(ItemIdIsNormal(lpp));
@ -745,7 +748,8 @@ heapgettup(HeapScanDesc scan,
LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lines = PageGetMaxOffsetNumber((Page) dp);
linesleft = lines;
if (backward)
@ -832,7 +836,8 @@ heapgettup_pagemode(HeapScanDesc scan,
lineindex = scan->rs_cindex + 1;
}
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, scan->rs_snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lines = scan->rs_ntuples;
/* page and lineindex now reference the next visible tid */
@ -875,7 +880,8 @@ heapgettup_pagemode(HeapScanDesc scan,
page = scan->rs_cblock; /* current page */
}
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, scan->rs_snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lines = scan->rs_ntuples;
if (!scan->rs_inited)
@ -908,7 +914,8 @@ heapgettup_pagemode(HeapScanDesc scan,
heapgetpage(scan, page);
/* Since the tuple was previously fetched, needn't lock page here */
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, scan->rs_snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
lpp = PageGetItemId(dp, lineoff);
Assert(ItemIdIsNormal(lpp));
@ -1027,7 +1034,8 @@ heapgettup_pagemode(HeapScanDesc scan,
heapgetpage(scan, page);
dp = BufferGetPage(scan->rs_cbuf, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
dp = BufferGetPage(scan->rs_cbuf, scan->rs_snapshot, scan->rs_rd,
BGP_TEST_FOR_OLD_SNAPSHOT);
lines = scan->rs_ntuples;
linesleft = lines;
if (backward)
@ -1871,7 +1879,7 @@ heap_fetch(Relation relation,
* Need share lock on buffer to examine tuple commit status.
*/
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
page = BufferGetPage(buffer, snapshot, relation, BGP_TEST_FOR_OLD_SNAPSHOT);
/*
* We'd better check for out-of-range offnum in case of VACUUM since the
@ -2200,7 +2208,8 @@ heap_get_latest_tid(Relation relation,
*/
buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&ctid));
LockBuffer(buffer, BUFFER_LOCK_SHARE);
page = BufferGetPage(buffer, NULL, NULL, BGP_NO_SNAPSHOT_TEST);
page = BufferGetPage(buffer, snapshot, relation,
BGP_TEST_FOR_OLD_SNAPSHOT);
/*
* Check for bogus item number. This is not treated as an error

11
src/backend/access/heap/pruneheap.c
View File

@ -92,12 +92,21 @@ heap_page_prune_opt(Relation relation, Buffer buffer)
* need to use the horizon that includes slots, otherwise the data-only
* horizon can be used. Note that the toast relation of user defined
* relations are *not* considered catalog relations.
*
* It is OK to apply the old snapshot limit before acquiring the cleanup
* lock because the worst that can happen is that we are not quite as
* aggressive about the cleanup (by however many transaction IDs are
* consumed between this point and acquiring the lock). This allows us to
* save significant overhead in the case where the page is found not to be
* prunable.
*/
if (IsCatalogRelation(relation) ||
RelationIsAccessibleInLogicalDecoding(relation))
OldestXmin = RecentGlobalXmin;
else
OldestXmin = RecentGlobalDataXmin;
OldestXmin =
TransactionIdLimitedForOldSnapshots(RecentGlobalDataXmin,
relation);
Assert(TransactionIdIsValid(OldestXmin));