* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/gin/ginget.c,v 1.30.4.1 2010/07/31 00:31:04 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/gin/ginget.c,v 1.30.4.2 2010/08/01 19:16:47 tgl Exp $
*-------------------------------------------------------------------------
*/
int res;
if (GinPageGetOpaque(page)->flags & GIN_DELETED)
- /* page was deleted by concurrent vacuum */
+ /* page was deleted by concurrent vacuum */
return false;
/*
* scan page to find equal or first greater value
*/
-
for (*off = FirstOffsetNumber; *off <= maxoff; (*off)++)
{
res = compareItemPointers(item, (ItemPointer) GinDataPageGetItem(page, *off));
}
}
+/* convenience function for invoking a key's consistentFn */
+static inline bool
+callConsistentFn(GinState *ginstate, GinScanKey key)
+{
+ /*
+ * Initialize recheckCurItem in case the consistentFn doesn't know it
+ * should set it. The safe assumption in that case is to force recheck.
+ */
+ key->recheckCurItem = true;
+
+ return DatumGetBool(FunctionCall6(&ginstate->consistentFn[key->attnum - 1],
+ PointerGetDatum(key->entryRes),
+ UInt16GetDatum(key->strategy),
+ key->query,
+ UInt32GetDatum(key->nentries),
+ PointerGetDatum(key->extra_data),
+ PointerGetDatum(&key->recheckCurItem)));
+}
+
#define gin_rand() (((double) random()) / ((double) MAX_RANDOM_VALUE))
#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.
+ *
+ * Item pointers must be 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
+ * not allowed to return both a lossy page pointer and exact (regular)
+ * item pointers for the same page. (Doing so would break the key-combination
+ * logic in keyGetItem and scanGetItem; see comment in scanGetItem.) In the
+ * current implementation this is guaranteed by the behavior of tidbitmaps.
*/
static void
entryGetItem(Relation index, GinScanEntry entry)
* item pointer (including the case where the item pointer is a lossy page
* pointer).
*
- * Note: lossy page could be returned after single items from the same page.
- * This is OK since the results will just be used to build a bitmap; we'll
- * set a bitmap entry more than once, but never actually return a row twice.
+ * Item pointers must be returned in ascending order.
+ *
+ * Note: this can return a "lossy page" item pointer, indicating that the
+ * key potentially matches all items on that heap page. However, it is
+ * not allowed to return both a lossy page pointer and exact (regular)
+ * item pointers for the same page. (Doing so would break the key-combination
+ * logic in scanGetItem.)
*/
static void
keyGetItem(Relation index, GinState *ginstate, MemoryContext tempCtx,
GinScanKey key, ItemPointer advancePast)
{
ItemPointerData myAdvancePast = *advancePast;
+ ItemPointerData curPageLossy;
uint32 i;
uint32 lossyEntry;
bool haveLossyEntry;
myAdvancePast = key->curItem;
/*
- * Prepare entryRes array to be passed to consistentFn.
- *
- * If key->nentries == 1 then the consistentFn should always succeed,
- * but we must call it anyway to find out the recheck status.
- *
* Lossy-page entries pose a problem, since we don't know the correct
* entryRes state to pass to the consistentFn, and we also don't know
* what its combining logic will be (could be AND, OR, or even NOT).
- * Our strategy for a single lossy-page entry is to try the
- * consistentFn both ways and return a hit if it accepts either one
- * (forcing the hit to be marked lossy so it will be rechecked).
+ * If the logic is OR then the consistentFn might succeed for all
+ * items in the lossy page even when none of the other entries match.
+ *
+ * If we have a single lossy-page entry then we check to see if the
+ * consistentFn will succeed with only that entry TRUE. If so,
+ * we return a lossy-page pointer to indicate that the whole heap
+ * page must be checked. (On the next call, we'll advance past all
+ * regular and lossy entries for this page before resuming search,
+ * thus ensuring that we never return both regular and lossy pointers
+ * for the same page.)
*
* This idea could be generalized to more than one lossy-page entry,
* but ideally lossy-page entries should be infrequent so it would
- * seldom be the case that we have more than one. If we do find more
- * than one, we just punt and return the item as lossy.
+ * seldom be the case that we have more than one at once. So it
+ * doesn't seem worth the extra complexity to optimize that case.
+ * If we do find more than one, we just punt and return a lossy-page
+ * pointer always.
*
* Note that only lossy-page entries pointing to the current item's
- * page should trigger this processing.
+ * page should trigger this processing; we might have future lossy
+ * pages in the entry array, but they aren't relevant yet.
*/
+ ItemPointerSetLossyPage(&curPageLossy,
+ GinItemPointerGetBlockNumber(&key->curItem));
+
lossyEntry = 0;
haveLossyEntry = false;
for (i = 0; i < key->nentries; i++)
{
entry = key->scanEntry + i;
-
- if (entry->isFinished)
- key->entryRes[i] = FALSE;
- else if (ItemPointerIsLossyPage(&entry->curItem) &&
- GinItemPointerGetBlockNumber(&entry->curItem) ==
- GinItemPointerGetBlockNumber(&key->curItem))
+ if (entry->isFinished == FALSE &&
+ compareItemPointers(&entry->curItem, &curPageLossy) == 0)
{
if (haveLossyEntry)
{
- /* Too many lossy entries, punt */
+ /* Multiple lossy entries, punt */
+ key->curItem = curPageLossy;
key->recheckCurItem = true;
return;
}
lossyEntry = i;
haveLossyEntry = true;
- /* initially assume TRUE */
- key->entryRes[i] = TRUE;
}
- else if (compareItemPointers(&entry->curItem, &key->curItem) == 0)
- key->entryRes[i] = TRUE;
- else
- key->entryRes[i] = FALSE;
}
+ /* prepare for calling consistentFn in temp context */
oldCtx = MemoryContextSwitchTo(tempCtx);
+ if (haveLossyEntry)
+ {
+ /* Single lossy-page entry, so see if whole page matches */
+ memset(key->entryRes, FALSE, key->nentries);
+ key->entryRes[lossyEntry] = TRUE;
+
+ if (callConsistentFn(ginstate, key))
+ {
+ /* Yes, so clean up ... */
+ MemoryContextSwitchTo(oldCtx);
+ MemoryContextReset(tempCtx);
+
+ /* and return lossy pointer for whole page */
+ key->curItem = curPageLossy;
+ key->recheckCurItem = true;
+ return;
+ }
+ }
+
/*
- * Initialize recheckCurItem in case the consistentFn doesn't know it
- * should set it. The safe assumption in that case is to force
- * recheck.
+ * At this point we know that we don't need to return a lossy
+ * whole-page pointer, but we might have matches for individual exact
+ * item pointers, possibly in combination with a lossy pointer. Our
+ * strategy if there's a lossy pointer is to try the consistentFn both
+ * ways and return a hit if it accepts either one (forcing the hit to
+ * be marked lossy so it will be rechecked).
+ *
+ * Prepare entryRes array to be passed to consistentFn.
+ *
+ * (If key->nentries == 1 then the consistentFn should always succeed,
+ * but we must call it anyway to find out the recheck status.)
*/
- key->recheckCurItem = true;
+ for (i = 0; i < key->nentries; i++)
+ {
+ entry = key->scanEntry + i;
+ if (entry->isFinished == FALSE &&
+ compareItemPointers(&entry->curItem, &key->curItem) == 0)
+ key->entryRes[i] = TRUE;
+ else
+ key->entryRes[i] = FALSE;
+ }
+ if (haveLossyEntry)
+ key->entryRes[lossyEntry] = TRUE;
- res = DatumGetBool(FunctionCall6(&ginstate->consistentFn[key->attnum - 1],
- PointerGetDatum(key->entryRes),
- UInt16GetDatum(key->strategy),
- key->query,
- UInt32GetDatum(key->nentries),
- PointerGetDatum(key->extra_data),
- PointerGetDatum(&key->recheckCurItem)));
+ res = callConsistentFn(ginstate, key);
if (!res && haveLossyEntry)
{
/* try the other way for the lossy item */
key->entryRes[lossyEntry] = FALSE;
- key->recheckCurItem = true;
- res = DatumGetBool(FunctionCall6(&ginstate->consistentFn[key->attnum - 1],
- PointerGetDatum(key->entryRes),
- UInt16GetDatum(key->strategy),
- key->query,
- UInt32GetDatum(key->nentries),
- PointerGetDatum(key->extra_data),
- PointerGetDatum(&key->recheckCurItem)));
+ res = callConsistentFn(ginstate, key);
}
+ /* clean up after consistentFn calls */
MemoryContextSwitchTo(oldCtx);
MemoryContextReset(tempCtx);
GinScanOpaque so = (GinScanOpaque) scan->opaque;
MemoryContext oldCtx;
bool recheck,
- keyrecheck,
match;
int i;
pendingPosition pos;
continue;
/*
- * Matching of entries of one row is finished, so check row by
- * consistent function.
+ * Matching of entries of one row is finished, so check row using
+ * consistent functions.
*/
oldCtx = MemoryContextSwitchTo(so->tempCtx);
recheck = false;
{
GinScanKey key = so->keys + i;
- keyrecheck = true;
-
- if (!DatumGetBool(FunctionCall6(&so->ginstate.consistentFn[key->attnum - 1],
- PointerGetDatum(key->entryRes),
- UInt16GetDatum(key->strategy),
- key->query,
- UInt32GetDatum(key->nentries),
- PointerGetDatum(key->extra_data),
- PointerGetDatum(&keyrecheck))))
+ if (!callConsistentFn(&so->ginstate, key))
{
match = false;
break;
}
-
- recheck |= keyrecheck;
+ recheck |= key->recheckCurItem;
}
MemoryContextSwitchTo(oldCtx);
Assert(!ItemPointerIsMax(item));
- /*
+ /*----------
* Now *item contains first ItemPointer after previous result.
*
* The item is a valid hit only if all the keys returned 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++)
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