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Allow pg_class xid & multixid horizons to not be set.

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This allows table AMs that don't need these horizons. This was already
documented in the tableam relation_set_new_filenode callback, but an
assert prevented if from actually working (the test AM code contained
the change itself). Defang the asserts in the general code, and move
the stronger ones into heap AM.

Relatedly, after CLUSTER/VACUUM, we'd always assign a relfrozenxid /
relminmxid. Change the table_relation_copy_for_cluster() interface to
allow the AM to overwrite the horizons that get set on the pg_class
entry.  This'd also in the future allow AMs like heap to compute a
relfrozenxid during rewrite that's the table's actual minimum rather
than a pre-determined value.  Arguably it'd have been better to move
the whole computation / setting of those values into the callback, but
it seems likely that for other reasons it'd be better to be able to
use one value to vacuum/cluster multiple tables (e.g. a toast's
horizon shouldn't be different than the table's).

Reported-By: Heikki Linnakangas
Author: Andres Freund
Discussion: https://postgr.es/m/9a7fb9cc-2419-5db7-8840-ddc10c93f122@iki.fi
This commit is contained in:
Andres Freund
2019-04-23 21:42:12 -07:00
parent 7ad1cd31bf
commit fdc7efcc30
6 changed files with 83 additions and 45 deletions
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24
src/backend/commands/cluster.c
View File

@ -870,19 +870,17 @@ copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
* FreezeXid will become the table's new relfrozenxid, and that mustn't go
* backwards, so take the max.
*/
if (TransactionIdPrecedes(FreezeXid, OldHeap->rd_rel->relfrozenxid))
if (TransactionIdIsValid(OldHeap->rd_rel->relfrozenxid) &&
TransactionIdPrecedes(FreezeXid, OldHeap->rd_rel->relfrozenxid))
FreezeXid = OldHeap->rd_rel->relfrozenxid;
/*
* MultiXactCutoff, similarly, shouldn't go backwards either.
*/
if (MultiXactIdPrecedes(MultiXactCutoff, OldHeap->rd_rel->relminmxid))
if (MultiXactIdIsValid(OldHeap->rd_rel->relminmxid) &&
MultiXactIdPrecedes(MultiXactCutoff, OldHeap->rd_rel->relminmxid))
MultiXactCutoff = OldHeap->rd_rel->relminmxid;
/* return selected values to caller */
*pFreezeXid = FreezeXid;
*pCutoffMulti = MultiXactCutoff;
/*
* Decide whether to use an indexscan or seqscan-and-optional-sort to scan
* the OldHeap. We know how to use a sort to duplicate the ordering of a
@ -915,13 +913,19 @@ copy_table_data(Oid OIDNewHeap, Oid OIDOldHeap, Oid OIDOldIndex, bool verbose,
/*
* Hand of the actual copying to AM specific function, the generic code
* cannot know how to deal with visibility across AMs.
* cannot know how to deal with visibility across AMs. Note that this
* routine is allowed to set FreezeXid / MultiXactCutoff to different
* values (e.g. because the AM doesn't use freezing).
*/
table_relation_copy_for_cluster(OldHeap, NewHeap, OldIndex, use_sort,
OldestXmin, FreezeXid, MultiXactCutoff,
OldestXmin, &FreezeXid, &MultiXactCutoff,
&num_tuples, &tups_vacuumed,
&tups_recently_dead);
/* return selected values to caller, get set as relfrozenxid/minmxid */
*pFreezeXid = FreezeXid;
*pCutoffMulti = MultiXactCutoff;
/* Reset rd_toastoid just to be tidy --- it shouldn't be looked at again */
NewHeap->rd_toastoid = InvalidOid;
@ -1118,9 +1122,9 @@ swap_relation_files(Oid r1, Oid r2, bool target_is_pg_class,
/* set rel1's frozen Xid and minimum MultiXid */
if (relform1->relkind != RELKIND_INDEX)
{
Assert(TransactionIdIsNormal(frozenXid));
Assert(!TransactionIdIsValid(frozenXid) ||
TransactionIdIsNormal(frozenXid));
relform1->relfrozenxid = frozenXid;
Assert(MultiXactIdIsValid(cutoffMulti));
relform1->relminmxid = cutoffMulti;
}

53
src/backend/commands/vacuum.c
View File

@ -1313,36 +1313,61 @@ vac_update_datfrozenxid(void)
/*
* Only consider relations able to hold unfrozen XIDs (anything else
* should have InvalidTransactionId in relfrozenxid anyway.)
* should have InvalidTransactionId in relfrozenxid anyway).
*/
if (classForm->relkind != RELKIND_RELATION &&
classForm->relkind != RELKIND_MATVIEW &&
classForm->relkind != RELKIND_TOASTVALUE)
{
Assert(!TransactionIdIsValid(classForm->relfrozenxid));
Assert(!MultiXactIdIsValid(classForm->relminmxid));
continue;
Assert(TransactionIdIsNormal(classForm->relfrozenxid));
Assert(MultiXactIdIsValid(classForm->relminmxid));
}
/*
* Some table AMs might not need per-relation xid / multixid
* horizons. It therefore seems reasonable to allow relfrozenxid and
* relminmxid to not be set (i.e. set to their respective Invalid*Id)
* independently. Thus validate and compute horizon for each only if
* set.
*
* If things are working properly, no relation should have a
* relfrozenxid or relminmxid that is "in the future". However, such
* cases have been known to arise due to bugs in pg_upgrade. If we
* see any entries that are "in the future", chicken out and don't do
* anything. This ensures we won't truncate clog before those
* relations have been scanned and cleaned up.
* anything. This ensures we won't truncate clog & multixact SLRUs
* before those relations have been scanned and cleaned up.
*/
if (TransactionIdPrecedes(lastSaneFrozenXid, classForm->relfrozenxid) ||
MultiXactIdPrecedes(lastSaneMinMulti, classForm->relminmxid))
if (TransactionIdIsValid(classForm->relfrozenxid))
{
bogus = true;
break;
Assert(TransactionIdIsNormal(classForm->relfrozenxid));
/* check for values in the future */
if (TransactionIdPrecedes(lastSaneFrozenXid, classForm->relfrozenxid))
{
bogus = true;
break;
}
/* determine new horizon */
if (TransactionIdPrecedes(classForm->relfrozenxid, newFrozenXid))
newFrozenXid = classForm->relfrozenxid;
}
if (TransactionIdPrecedes(classForm->relfrozenxid, newFrozenXid))
newFrozenXid = classForm->relfrozenxid;
if (MultiXactIdIsValid(classForm->relminmxid))
{
/* check for values in the future */
if (MultiXactIdPrecedes(lastSaneMinMulti, classForm->relminmxid))
{
bogus = true;
break;
}
if (MultiXactIdPrecedes(classForm->relminmxid, newMinMulti))
newMinMulti = classForm->relminmxid;
/* determine new horizon */
if (MultiXactIdPrecedes(classForm->relminmxid, newMinMulti))
newMinMulti = classForm->relminmxid;
}
}
/* we're done with pg_class */