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Improve GIN indexscan cost estimation.

Browse Source 
The better estimate requires more statistics than we previously stored:
in particular, counts of "entry" versus "data" pages within the index,
as well as knowledge of the number of distinct key values.  We collect
this information during initial index build and update it during VACUUM,
storing the info in new fields on the index metapage.  No initdb is
required because these fields will read as zeroes in a pre-existing
index, and the new gincostestimate code is coded to behave (reasonably)
sanely if they are zeroes.

Teodor Sigaev, reviewed by Jan Urbanski, Tom Lane, and Itagaki Takahiro.
This commit is contained in:
Tom Lane
2010-10-17 20:52:32 -04:00
parent cd0e825321
commit 48c7d9f6ff
10 changed files with 561 additions and 42 deletions
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56
src/backend/access/gin/gininsert.c
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@ -27,6 +27,7 @@ typedef struct
{
GinState ginstate;
double indtuples;
GinStatsData buildStats;
MemoryContext tmpCtx;
MemoryContext funcCtx;
BuildAccumulator accum;
@ -97,8 +98,10 @@ createPostingTree(Relation index, ItemPointerData *items, uint32 nitems)
* GinFormTuple().
*/
static IndexTuple
addItemPointersToTuple(Relation index, GinState *ginstate, GinBtreeStack *stack,
IndexTuple old, ItemPointerData *items, uint32 nitem, bool isBuild)
addItemPointersToTuple(Relation index, GinState *ginstate,
GinBtreeStack *stack, IndexTuple old,
ItemPointerData *items, uint32 nitem,
GinStatsData *buildStats)
{
Datum key = gin_index_getattr(ginstate, old);
OffsetNumber attnum = gintuple_get_attrnum(ginstate, old);
@ -128,11 +131,15 @@ addItemPointersToTuple(Relation index, GinState *ginstate, GinBtreeStack *stack,
GinSetPostingTree(res, postingRoot);
gdi = prepareScanPostingTree(index, postingRoot, FALSE);
gdi->btree.isBuild = isBuild;
gdi->btree.isBuild = (buildStats != NULL);
insertItemPointer(gdi, items, nitem);
ginInsertItemPointer(gdi, items, nitem, buildStats);
pfree(gdi);
/* During index build, count the newly-added data page */
if (buildStats)
buildStats->nDataPages++;
}
return res;
@ -140,18 +147,25 @@ addItemPointersToTuple(Relation index, GinState *ginstate, GinBtreeStack *stack,
/*
* Inserts only one entry to the index, but it can add more than 1 ItemPointer.
*
* During an index build, buildStats is non-null and the counters
* it contains should be incremented as needed.
*/
void
ginEntryInsert(Relation index, GinState *ginstate,
OffsetNumber attnum, Datum value,
ItemPointerData *items, uint32 nitem,
bool isBuild)
GinStatsData *buildStats)
{
GinBtreeData btree;
GinBtreeStack *stack;
IndexTuple itup;
Page page;
/* During index build, count the to-be-inserted entry */
if (buildStats)
buildStats->nEntries++;
prepareEntryScan(&btree, index, attnum, value, ginstate);
stack = ginFindLeafPage(&btree, NULL);
@ -174,14 +188,15 @@ ginEntryInsert(Relation index, GinState *ginstate,
/* insert into posting tree */
gdi = prepareScanPostingTree(index, rootPostingTree, FALSE);
gdi->btree.isBuild = isBuild;
insertItemPointer(gdi, items, nitem);
gdi->btree.isBuild = (buildStats != NULL);
ginInsertItemPointer(gdi, items, nitem, buildStats);
pfree(gdi);
return;
}
itup = addItemPointersToTuple(index, ginstate, stack, itup, items, nitem, isBuild);
itup = addItemPointersToTuple(index, ginstate, stack, itup,
items, nitem, buildStats);
btree.isDelete = TRUE;
}
@ -195,13 +210,14 @@ ginEntryInsert(Relation index, GinState *ginstate,
/* Add the rest, making a posting tree if necessary */
IndexTuple previtup = itup;
itup = addItemPointersToTuple(index, ginstate, stack, previtup, items + 1, nitem - 1, isBuild);
itup = addItemPointersToTuple(index, ginstate, stack, previtup,
items + 1, nitem - 1, buildStats);
pfree(previtup);
}
}
btree.entry = itup;
ginInsertValue(&btree, stack);
ginInsertValue(&btree, stack, buildStats);
pfree(itup);
}
@ -260,7 +276,8 @@ ginBuildCallback(Relation index, HeapTuple htup, Datum *values,
{
/* there could be many entries, so be willing to abort here */
CHECK_FOR_INTERRUPTS();
ginEntryInsert(index, &buildstate->ginstate, attnum, entry, list, nlist, TRUE);
ginEntryInsert(index, &buildstate->ginstate, attnum, entry,
list, nlist, &buildstate->buildStats);
}
MemoryContextReset(buildstate->tmpCtx);
@ -292,6 +309,8 @@ ginbuild(PG_FUNCTION_ARGS)
RelationGetRelationName(index));
initGinState(&buildstate.ginstate, index);
buildstate.indtuples = 0;
memset(&buildstate.buildStats, 0, sizeof(GinStatsData));
/* initialize the meta page */
MetaBuffer = GinNewBuffer(index);
@ -331,8 +350,8 @@ ginbuild(PG_FUNCTION_ARGS)
UnlockReleaseBuffer(RootBuffer);
END_CRIT_SECTION();
/* build the index */
buildstate.indtuples = 0;
/* count the root as first entry page */
buildstate.buildStats.nEntryPages++;
/*
* create a temporary memory context that is reset once for each tuple
@ -367,12 +386,19 @@ ginbuild(PG_FUNCTION_ARGS)
{
/* there could be many entries, so be willing to abort here */
CHECK_FOR_INTERRUPTS();
ginEntryInsert(index, &buildstate.ginstate, attnum, entry, list, nlist, TRUE);
ginEntryInsert(index, &buildstate.ginstate, attnum, entry,
list, nlist, &buildstate.buildStats);
}
MemoryContextSwitchTo(oldCtx);
MemoryContextDelete(buildstate.tmpCtx);
/*
* Update metapage stats
*/
buildstate.buildStats.nTotalPages = RelationGetNumberOfBlocks(index);
ginUpdateStats(index, &buildstate.buildStats);
/*
* Return statistics
*/
@ -401,7 +427,7 @@ ginHeapTupleInsert(Relation index, GinState *ginstate, OffsetNumber attnum, Datu
return 0;
for (i = 0; i < nentries; i++)
ginEntryInsert(index, ginstate, attnum, entries[i], item, 1, FALSE);
ginEntryInsert(index, ginstate, attnum, entries[i], item, 1, NULL);
return nentries;
}