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Re-allow testing of GiST buffered builds.

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Commit 16fa9b2b3 broke the ability to reliably test GiST buffered builds,
because it caused sorted builds to be done instead if sortsupport is
available, regardless of any attempt to override that.  While a would-be
test case could try to work around that by choosing an opclass that has
no sortsupport function, coverage would be silently lost the moment
someone decides it'd be a good idea to add a sortsupport function.

Hence, rearrange the logic in gistbuild() so that if "buffering = on"
is specified in CREATE INDEX, we will use that method, sortsupport or no.

Also document the interaction between sorting and the buffering
parameter, as 16fa9b2b3 failed to do.

(Note that in fact we still lack any test coverage of buffered builds,
but this is a prerequisite to adding a non-fragile test.)

Discussion: https://postgr.es/m/3249980.1602532990@sss.pgh.pa.us
This commit is contained in:
Tom Lane
2020-10-12 17:09:50 -04:00
parent 397ea901e8
commit 78c0b6ed27
3 changed files with 77 additions and 53 deletions
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60
src/backend/access/gist/gistbuild.c
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@ -180,9 +180,7 @@ gistbuild(Relation heap, Relation index, IndexInfo *indexInfo)
MemoryContext oldcxt = CurrentMemoryContext;
int fillfactor;
Oid SortSupportFnOids[INDEX_MAX_KEYS];
bool hasallsortsupports;
int keyscount = IndexRelationGetNumberOfKeyAttributes(index);
GiSTOptions *options = NULL;
GiSTOptions *options = (GiSTOptions *) index->rd_options;
/*
* We expect to be called exactly once for any index relation. If that's
@ -192,9 +190,6 @@ gistbuild(Relation heap, Relation index, IndexInfo *indexInfo)
elog(ERROR, "index \"%s\" already contains data",
RelationGetRelationName(index));
if (index->rd_options)
options = (GiSTOptions *) index->rd_options;
buildstate.indexrel = index;
buildstate.heaprel = heap;
buildstate.sortstate = NULL;
@ -208,33 +203,17 @@ gistbuild(Relation heap, Relation index, IndexInfo *indexInfo)
buildstate.giststate->tempCxt = createTempGistContext();
/*
* Choose build strategy. If all keys support sorting, do that. Otherwise
* the default strategy is switch to buffering mode when the index grows
* too large to fit in cache.
* Choose build strategy. First check whether the user specified to use
* buffering mode. (The use-case for that in the field is somewhat
* questionable perhaps, but it's important for testing purposes.)
*/
hasallsortsupports = true;
for (int i = 0; i < keyscount; i++)
{
SortSupportFnOids[i] = index_getprocid(index, i + 1,
GIST_SORTSUPPORT_PROC);
if (!OidIsValid(SortSupportFnOids[i]))
{
hasallsortsupports = false;
break;
}
}
if (hasallsortsupports)
{
buildstate.buildMode = GIST_SORTED_BUILD;
}
else if (options)
if (options)
{
if (options->buffering_mode == GIST_OPTION_BUFFERING_ON)
buildstate.buildMode = GIST_BUFFERING_STATS;
else if (options->buffering_mode == GIST_OPTION_BUFFERING_OFF)
buildstate.buildMode = GIST_BUFFERING_DISABLED;
else
else /* must be "auto" */
buildstate.buildMode = GIST_BUFFERING_AUTO;
}
else
@ -242,6 +221,28 @@ gistbuild(Relation heap, Relation index, IndexInfo *indexInfo)
buildstate.buildMode = GIST_BUFFERING_AUTO;
}
/*
* Unless buffering mode was forced, see if we can use sorting instead.
*/
if (buildstate.buildMode != GIST_BUFFERING_STATS)
{
bool hasallsortsupports = true;
int keyscount = IndexRelationGetNumberOfKeyAttributes(index);
for (int i = 0; i < keyscount; i++)
{
SortSupportFnOids[i] = index_getprocid(index, i + 1,
GIST_SORTSUPPORT_PROC);
if (!OidIsValid(SortSupportFnOids[i]))
{
hasallsortsupports = false;
break;
}
}
if (hasallsortsupports)
buildstate.buildMode = GIST_SORTED_BUILD;
}
/*
* Calculate target amount of free space to leave on pages.
*/
@ -852,7 +853,10 @@ gistBuildCallback(Relation index,
* and switch to buffering mode if it has.
*
* To avoid excessive calls to smgrnblocks(), only check this every
* BUFFERING_MODE_SWITCH_CHECK_STEP index tuples
* BUFFERING_MODE_SWITCH_CHECK_STEP index tuples.
*
* In 'stats' state, switch as soon as we have seen enough tuples to have
* some idea of the average tuple size.
*/
if ((buildstate->buildMode == GIST_BUFFERING_AUTO &&
buildstate->indtuples % BUFFERING_MODE_SWITCH_CHECK_STEP == 0 &&