From e20c70cb0fa74d5bffa080e21a99b44bf0768667 Mon Sep 17 00:00:00 2001
From: Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date: Wed, 29 Jan 2014 17:53:39 +0200
Subject: [PATCH] Allow skipping some items in a multi-key GIN search.
In a multi-key search, ie. something like "col @> 'foo' AND col @> 'bar'",
as soon as we find the next item that matches the first criteria, we don't
need to check the second criteria for TIDs smaller the first match. That
saves a lot of effort, especially if one of the terms is rare, while the
second occurs very frequently.
Based on ideas from Alexander Korotkov's fast scan patch.
---
src/backend/access/gin/ginget.c | 460 +++++++++++++++++---------------
1 file changed, 250 insertions(+), 210 deletions(-)
diff --git a/src/backend/access/gin/ginget.c b/src/backend/access/gin/ginget.c
index 4bdbd4525d5..40abb3971e2 100644
--- a/src/backend/access/gin/ginget.c
+++ b/src/backend/access/gin/ginget.c
@@ -67,29 +67,6 @@ callConsistentFn(GinState *ginstate, GinScanKey key)
PointerGetDatum(key->queryCategories)));
}
-/*
- * Tries to refind previously taken ItemPointer on a posting page.
- */
-static bool
-needToStepRight(Page page, ItemPointer item)
-{
- if (GinPageGetOpaque(page)->flags & GIN_DELETED)
- /* page was deleted by concurrent vacuum */
- return true;
-
- if (ginCompareItemPointers(item, GinDataPageGetRightBound(page)) > 0
- && !GinPageRightMost(page))
- {
- /*
- * the item we're looking is > the right bound of the page, so it
- * can't be on this page.
- */
- return true;
- }
-
- return false;
-}
-
/*
* Goes to the next page if current offset is outside of bounds
*/
@@ -447,8 +424,7 @@ restartScanEntry:
page = BufferGetPage(entry->buffer);
/*
- * Copy page content to memory to avoid keeping it locked for
- * a long time.
+ * Load the first page into memory.
*/
entry->list = GinDataLeafPageGetItems(page, &entry->nlist);
@@ -518,88 +494,78 @@ startScan(IndexScanDesc scan)
}
/*
- * Gets next ItemPointer from PostingTree. Note, that we copy
- * page into GinScanEntry->list array and unlock page, but keep it pinned
- * to prevent interference with vacuum
+ * Load the next batch of item pointers from a posting tree.
+ *
+ * Note that we copy the page into GinScanEntry->list array and unlock it, but
+ * keep it pinned to prevent interference with vacuum.
*/
static void
-entryGetNextItem(GinState *ginstate, GinScanEntry entry)
+entryLoadMoreItems(GinState *ginstate, GinScanEntry entry, ItemPointerData advancePast)
{
Page page;
int i;
+ LockBuffer(entry->buffer, GIN_SHARE);
+ page = BufferGetPage(entry->buffer);
for (;;)
{
- if (entry->offset < entry->nlist)
+ entry->offset = InvalidOffsetNumber;
+ if (entry->list)
{
- entry->curItem = entry->list[entry->offset++];
- return;
+ pfree(entry->list);
+ entry->list = NULL;
+ entry->nlist = 0;
}
- LockBuffer(entry->buffer, GIN_SHARE);
- page = BufferGetPage(entry->buffer);
- for (;;)
+ /*
+ * We've processed all the entries on this page. If it was the last
+ * page in the tree, we're done.
+ */
+ if (GinPageRightMost(page))
{
- /*
- * It's needed to go by right link. During that we should refind
- * first ItemPointer greater that stored
- */
- if (GinPageRightMost(page))
- {
- UnlockReleaseBuffer(entry->buffer);
- ItemPointerSetInvalid(&entry->curItem);
- entry->buffer = InvalidBuffer;
- entry->isFinished = TRUE;
- return;
- }
+ UnlockReleaseBuffer(entry->buffer);
+ entry->buffer = InvalidBuffer;
+ entry->isFinished = TRUE;
+ return;
+ }
- entry->buffer = ginStepRight(entry->buffer,
- ginstate->index,
- GIN_SHARE);
- page = BufferGetPage(entry->buffer);
+ if (GinPageGetOpaque(page)->flags & GIN_DELETED)
+ continue; /* page was deleted by concurrent vacuum */
- entry->offset = InvalidOffsetNumber;
- if (entry->list)
- {
- pfree(entry->list);
- entry->list = NULL;
- }
+ /*
+ * Step to next page, following the right link. then find the first
+ * ItemPointer greater than advancePast.
+ */
+ entry->buffer = ginStepRight(entry->buffer,
+ ginstate->index,
+ GIN_SHARE);
+ page = BufferGetPage(entry->buffer);
+ /*
+ * The first item > advancePast might not be on this page, but
+ * somewhere to the right, if the page was split, or a non-match from
+ * another key in the query allowed us to skip some items from this
+ * entry. Keep following the right-links until we re-find the correct
+ * page.
+ */
+ if (!GinPageRightMost(page) &&
+ ginCompareItemPointers(&advancePast, GinDataPageGetRightBound(page)) >= 0)
+ {
/*
- * If the page was concurrently split, we have to re-find the
- * item we were stopped on. If the page was split more than once,
- * the item might not be on this page, but somewhere to the right.
- * Keep following the right-links until we re-find the correct
- * page.
+ * the item we're looking is > the right bound of the page, so it
+ * can't be on this page.
*/
- if (ItemPointerIsValid(&entry->curItem) &&
- needToStepRight(page, &entry->curItem))
- {
- continue;
- }
+ continue;
+ }
- entry->list = GinDataLeafPageGetItems(page, &entry->nlist);
+ entry->list = GinDataLeafPageGetItems(page, &entry->nlist);
- /* re-find the item we were stopped on. */
- if (ItemPointerIsValid(&entry->curItem))
- {
- for (i = 0; i < entry->nlist; i++)
- {
- if (ginCompareItemPointers(&entry->curItem,
- &entry->list[i]) < 0)
- {
- LockBuffer(entry->buffer, GIN_UNLOCK);
- entry->offset = i + 1;
- entry->curItem = entry->list[entry->offset - 1];
- return;
- }
- }
- }
- else
+ for (i = 0; i < entry->nlist; i++)
+ {
+ if (ginCompareItemPointers(&advancePast, &entry->list[i]) < 0)
{
LockBuffer(entry->buffer, GIN_UNLOCK);
- entry->offset = 1; /* scan all items on the page. */
- entry->curItem = entry->list[entry->offset - 1];
+ entry->offset = i;
return;
}
}
@@ -610,10 +576,10 @@ entryGetNextItem(GinState *ginstate, GinScanEntry entry)
#define dropItem(e) ( gin_rand() > ((double)GinFuzzySearchLimit)/((double)((e)->predictNumberResult)) )
/*
- * Sets entry->curItem to next heap item pointer for one entry of one scan key,
- * or sets entry->isFinished to TRUE if there are no more.
+ * Sets entry->curItem to next heap item pointer > advancePast, for one entry
+ * of one scan key, or sets entry->isFinished to TRUE if there are no more.
*
- * Item pointers must be returned in ascending order.
+ * Item pointers are returned in ascending order.
*
* Note: this can return a "lossy page" item pointer, indicating that the
* entry potentially matches all items on that heap page. However, it is
@@ -623,12 +589,20 @@ entryGetNextItem(GinState *ginstate, GinScanEntry entry)
* current implementation this is guaranteed by the behavior of tidbitmaps.
*/
static void
-entryGetItem(GinState *ginstate, GinScanEntry entry)
+entryGetItem(GinState *ginstate, GinScanEntry entry,
+ ItemPointerData advancePast)
{
Assert(!entry->isFinished);
+ Assert(!ItemPointerIsValid(&entry->curItem) ||
+ ginCompareItemPointers(&entry->curItem, &advancePast) <= 0);
+
if (entry->matchBitmap)
{
+ /* A bitmap result */
+ BlockNumber advancePastBlk = GinItemPointerGetBlockNumber(&advancePast);
+ OffsetNumber advancePastOff = GinItemPointerGetOffsetNumber(&advancePast);
+
do
{
if (entry->matchResult == NULL ||
@@ -645,6 +619,18 @@ entryGetItem(GinState *ginstate, GinScanEntry entry)
break;
}
+ /*
+ * If all the matches on this page are <= advancePast, skip
+ * to next page.
+ */
+ if (entry->matchResult->blockno < advancePastBlk ||
+ (entry->matchResult->blockno == advancePastBlk &&
+ entry->matchResult->offsets[entry->offset] <= advancePastOff))
+ {
+ entry->offset = entry->matchResult->ntuples;
+ continue;
+ }
+
/*
* Reset counter to the beginning of entry->matchResult. Note:
* entry->offset is still greater than matchResult->ntuples if
@@ -670,6 +656,17 @@ entryGetItem(GinState *ginstate, GinScanEntry entry)
break;
}
+ if (entry->matchResult->blockno == advancePastBlk)
+ {
+ /*
+ * Skip to the right offset on this page. We already checked
+ * in above loop that there is at least one item > advancePast
+ * on the page.
+ */
+ while (entry->matchResult->offsets[entry->offset] <= advancePastOff)
+ entry->offset++;
+ }
+
ItemPointerSet(&entry->curItem,
entry->matchResult->blockno,
entry->matchResult->offsets[entry->offset]);
@@ -678,29 +675,48 @@ entryGetItem(GinState *ginstate, GinScanEntry entry)
}
else if (!BufferIsValid(entry->buffer))
{
- entry->offset++;
- if (entry->offset <= entry->nlist)
- entry->curItem = entry->list[entry->offset - 1];
- else
+ /* A posting list from an entry tuple */
+ do
{
- ItemPointerSetInvalid(&entry->curItem);
- entry->isFinished = TRUE;
- }
+ if (entry->offset >= entry->nlist)
+ {
+ ItemPointerSetInvalid(&entry->curItem);
+ entry->isFinished = TRUE;
+ break;
+ }
+
+ entry->curItem = entry->list[entry->offset++];
+ } while (ginCompareItemPointers(&entry->curItem, &advancePast) <= 0);
+ /* XXX: shouldn't we apply the fuzzy search limit here? */
}
else
{
+ /* A posting tree */
do
{
- entryGetNextItem(ginstate, entry);
- } while (entry->isFinished == FALSE &&
- entry->reduceResult == TRUE &&
- dropItem(entry));
+ /* If we've processed the current batch, load more items */
+ while (entry->offset >= entry->nlist)
+ {
+ entryLoadMoreItems(ginstate, entry, advancePast);
+
+ if (entry->isFinished)
+ {
+ ItemPointerSetInvalid(&entry->curItem);
+ return;
+ }
+ }
+
+ entry->curItem = entry->list[entry->offset++];
+
+ } while (ginCompareItemPointers(&entry->curItem, &advancePast) <= 0 ||
+ (entry->reduceResult == TRUE && dropItem(entry)));
}
}
/*
- * Identify the "current" item among the input entry streams for this scan key,
- * and test whether it passes the scan key qual condition.
+ * Identify the "current" item among the input entry streams for this scan key
+ * that is greater than advancePast, and test whether it passes the scan key
+ * qual condition.
*
* The current item is the smallest curItem among the inputs. key->curItem
* is set to that value. key->curItemMatches is set to indicate whether that
@@ -719,7 +735,8 @@ entryGetItem(GinState *ginstate, GinScanEntry entry)
* logic in scanGetItem.)
*/
static void
-keyGetItem(GinState *ginstate, MemoryContext tempCtx, GinScanKey key)
+keyGetItem(GinState *ginstate, MemoryContext tempCtx, GinScanKey key,
+ ItemPointerData advancePast)
{
ItemPointerData minItem;
ItemPointerData curPageLossy;
@@ -729,11 +746,20 @@ keyGetItem(GinState *ginstate, MemoryContext tempCtx, GinScanKey key)
GinScanEntry entry;
bool res;
MemoryContext oldCtx;
+ bool allFinished;
Assert(!key->isFinished);
/*
- * Find the minimum of the active entry curItems.
+ * We might have already tested this item; if so, no need to repeat work.
+ * (Note: the ">" case can happen, if minItem is exact but we previously
+ * had to set curItem to a lossy-page pointer.)
+ */
+ if (ginCompareItemPointers(&key->curItem, &advancePast) > 0)
+ return;
+
+ /*
+ * Find the minimum item > advancePast among the active entry streams.
*
* Note: a lossy-page entry is encoded by a ItemPointer with max value for
* offset (0xffff), so that it will sort after any exact entries for the
@@ -741,16 +767,33 @@ keyGetItem(GinState *ginstate, MemoryContext tempCtx, GinScanKey key)
* pointers, which is good.
*/
ItemPointerSetMax(&minItem);
-
+ allFinished = true;
for (i = 0; i < key->nentries; i++)
{
entry = key->scanEntry[i];
- if (entry->isFinished == FALSE &&
- ginCompareItemPointers(&entry->curItem, &minItem) < 0)
- minItem = entry->curItem;
+
+ /*
+ * Advance this stream if necessary.
+ *
+ * In particular, since entry->curItem was initialized with
+ * ItemPointerSetMin, this ensures we fetch the first item for each
+ * entry on the first call.
+ */
+ while (entry->isFinished == FALSE &&
+ ginCompareItemPointers(&entry->curItem, &advancePast) <= 0)
+ {
+ entryGetItem(ginstate, entry, advancePast);
+ }
+
+ if (!entry->isFinished)
+ {
+ allFinished = FALSE;
+ if (ginCompareItemPointers(&entry->curItem, &minItem) < 0)
+ minItem = entry->curItem;
+ }
}
- if (ItemPointerIsMax(&minItem))
+ if (allFinished)
{
/* all entries are finished */
key->isFinished = TRUE;
@@ -758,15 +801,7 @@ keyGetItem(GinState *ginstate, MemoryContext tempCtx, GinScanKey key)
}
/*
- * We might have already tested this item; if so, no need to repeat work.
- * (Note: the ">" case can happen, if minItem is exact but we previously
- * had to set curItem to a lossy-page pointer.)
- */
- if (ginCompareItemPointers(&key->curItem, &minItem) >= 0)
- return;
-
- /*
- * OK, advance key->curItem and perform consistentFn test.
+ * OK, set key->curItem and perform consistentFn test.
*/
key->curItem = minItem;
@@ -895,117 +930,122 @@ keyGetItem(GinState *ginstate, MemoryContext tempCtx, GinScanKey key)
* keyGetItem() the combination logic is known only to the consistentFn.
*/
static bool
-scanGetItem(IndexScanDesc scan, ItemPointer advancePast,
+scanGetItem(IndexScanDesc scan, ItemPointerData advancePast,
ItemPointerData *item, bool *recheck)
{
GinScanOpaque so = (GinScanOpaque) scan->opaque;
- GinState *ginstate = &so->ginstate;
- ItemPointerData myAdvancePast = *advancePast;
uint32 i;
- bool allFinished;
bool match;
- for (;;)
+ /*----------
+ * Advance the scan keys in lock-step, until we find an item that matches
+ * all the keys. If any key reports isFinished, meaning its subset of the
+ * entries is exhausted, we can stop. Otherwise, set *item to the next
+ * matching item.
+ *
+ * This logic works only if a keyGetItem stream can never contain both
+ * exact and lossy pointers for the same page. Else we could have a
+ * case like
+ *
+ * stream 1 stream 2
+ * ... ...
+ * 42/6 42/7
+ * 50/1 42/0xffff
+ * ... ...
+ *
+ * We would conclude that 42/6 is not a match and advance stream 1,
+ * thus never detecting the match to the lossy pointer in stream 2.
+ * (keyGetItem has a similar problem versus entryGetItem.)
+ *----------
+ */
+ do
{
- /*
- * Advance any entries that are <= myAdvancePast. In particular,
- * since entry->curItem was initialized with ItemPointerSetMin, this
- * ensures we fetch the first item for each entry on the first call.
- */
- allFinished = TRUE;
-
- for (i = 0; i < so->totalentries; i++)
- {
- GinScanEntry entry = so->entries[i];
-
- while (entry->isFinished == FALSE &&
- ginCompareItemPointers(&entry->curItem,
- &myAdvancePast) <= 0)
- entryGetItem(ginstate, entry);
-
- if (entry->isFinished == FALSE)
- allFinished = FALSE;
- }
-
- if (allFinished)
- {
- /* all entries exhausted, so we're done */
- return false;
- }
-
- /*
- * Perform the consistentFn test for each scan key. If any key
- * reports isFinished, meaning its subset of the entries is exhausted,
- * we can stop. Otherwise, set *item to the minimum of the key
- * curItems.
- */
- ItemPointerSetMax(item);
-
- for (i = 0; i < so->nkeys; i++)
+ ItemPointerSetMin(item);
+ match = true;
+ for (i = 0; i < so->nkeys && match; i++)
{
GinScanKey key = so->keys + i;
- keyGetItem(&so->ginstate, so->tempCtx, key);
+ /* Fetch the next item for this key that is > advancePast. */
+ keyGetItem(&so->ginstate, so->tempCtx, key, advancePast);
if (key->isFinished)
- return false; /* finished one of keys */
-
- if (ginCompareItemPointers(&key->curItem, item) < 0)
- *item = key->curItem;
- }
+ return false;
- Assert(!ItemPointerIsMax(item));
+ /*
+ * If it's not a match, we can immediately conclude that nothing
+ * <= this item matches, without checking the rest of the keys.
+ */
+ if (!key->curItemMatches)
+ {
+ advancePast = key->curItem;
+ match = false;
+ break;
+ }
- /*----------
- * Now *item contains first ItemPointer after previous result.
- *
- * The item is a valid hit only if all the keys succeeded for either
- * that exact TID, or a lossy reference to the same page.
- *
- * This logic works only if a keyGetItem stream can never contain both
- * exact and lossy pointers for the same page. Else we could have a
- * case like
- *
- * stream 1 stream 2
- * ... ...
- * 42/6 42/7
- * 50/1 42/0xffff
- * ... ...
- *
- * We would conclude that 42/6 is not a match and advance stream 1,
- * thus never detecting the match to the lossy pointer in stream 2.
- * (keyGetItem has a similar problem versus entryGetItem.)
- *----------
- */
- match = true;
- for (i = 0; i < so->nkeys; i++)
- {
- GinScanKey key = so->keys + i;
+ /*
+ * It's a match. We can conclude that nothing < matches, so
+ * the other key streams can skip to this item.
+ *
+ * Beware of lossy pointers, though; from a lossy pointer, we
+ * can only conclude that nothing smaller than this *block*
+ * matches.
+ */
+ if (ItemPointerIsLossyPage(&key->curItem))
+ {
+ if (GinItemPointerGetBlockNumber(&advancePast) <
+ GinItemPointerGetBlockNumber(&key->curItem))
+ {
+ advancePast.ip_blkid = key->curItem.ip_blkid;
+ advancePast.ip_posid = 0;
+ }
+ }
+ else
+ {
+ Assert(key->curItem.ip_posid > 0);
+ advancePast = key->curItem;
+ advancePast.ip_posid--;
+ }
- if (key->curItemMatches)
+ /*
+ * If this is the first key, remember this location as a
+ * potential match.
+ *
+ * Otherwise, check if this is the same item that we checked the
+ * previous keys for (or a lossy pointer for the same page). If
+ * not, loop back to check the previous keys for this item (we
+ * will check this key again too, but keyGetItem returns quickly
+ * for that)
+ */
+ if (i == 0)
{
- if (ginCompareItemPointers(item, &key->curItem) == 0)
- continue;
- if (ItemPointerIsLossyPage(&key->curItem) &&
- GinItemPointerGetBlockNumber(&key->curItem) ==
- GinItemPointerGetBlockNumber(item))
- continue;
+ *item = key->curItem;
+ }
+ else
+ {
+ if (ItemPointerIsLossyPage(&key->curItem) ||
+ ItemPointerIsLossyPage(item))
+ {
+ Assert (GinItemPointerGetBlockNumber(&key->curItem) >= GinItemPointerGetBlockNumber(item));
+ match = (GinItemPointerGetBlockNumber(&key->curItem) ==
+ GinItemPointerGetBlockNumber(item));
+ }
+ else
+ {
+ Assert(ginCompareItemPointers(&key->curItem, item) >= 0);
+ match = (ginCompareItemPointers(&key->curItem, item) == 0);
+ }
}
- match = false;
- break;
}
+ } while (!match);
- if (match)
- break;
-
- /*
- * No hit. Update myAdvancePast to this TID, so that on the next pass
- * we'll move to the next possible entry.
- */
- myAdvancePast = *item;
- }
+ Assert(!ItemPointerIsMin(item));
/*
+ * Now *item contains the first ItemPointer after previous result that
+ * satisfied all the keys for that exact TID, or a lossy reference
+ * to the same page.
+ *
* We must return recheck = true if any of the keys are marked recheck.
*/
*recheck = false;
@@ -1536,7 +1576,7 @@ gingetbitmap(PG_FUNCTION_ARGS)
{
CHECK_FOR_INTERRUPTS();
- if (!scanGetItem(scan, &iptr, &iptr, &recheck))
+ if (!scanGetItem(scan, iptr, &iptr, &recheck))
break;
if (ItemPointerIsLossyPage(&iptr))
--
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