* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/access/gin/ginget.c,v 1.24 2009/03/25 22:19:01 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/access/gin/ginget.c,v 1.25 2009/04/05 11:32:01 teodor Exp $
*-------------------------------------------------------------------------
*/
* Sets key->curItem to new found heap item pointer for one scan key
* Returns isFinished, ie TRUE means we did NOT get a new item pointer!
* Also, *keyrecheck is set true if recheck is needed for this scan key.
+ * Note: lossy page could be returned after items from the same page.
*/
static bool
keyGetItem(Relation index, GinState *ginstate, MemoryContext tempCtx,
{
/*
* move forward from previously value and set new curItem, which is
- * minimal from entries->curItems
+ * minimal from entries->curItems. Lossy page is encoded by ItemPointer
+ * with max value for offset (0xffff), so if there is an non-lossy entries
+ * on lossy page they will returned too and after that the whole page.
+ * That's not a problem for resulting tidbitmap.
*/
ItemPointerSetMax(&key->curItem);
for (i = 0; i < key->nentries; i++)
{
/*
* Move forward only entries which was the least
- * on previous call
+ * on previous call, key->entryRes[i] points that
+ * current entry was a result of loop/call.
*/
if (entry->isFinished == FALSE && entryGetItem(index, entry) == FALSE)
{
}
/*
+ * Now key->curItem contains closest ItemPointer to previous result.
+ *
* if key->nentries == 1 then the consistentFn should always succeed,
* but we must call it anyway to find out the recheck status.
*/
- /* setting up array for consistentFn */
+ /*----------
+ * entryRes array is used for:
+ * - as an argument for consistentFn
+ * - entry->curItem with corresponding key->entryRes[i] == false are
+ * greater than key->curItem, so next loop/call they should be
+ * renewed by entryGetItem(). So, we need to set up an array before
+ * checking of lossy page.
+ *----------
+ */
for (i = 0; i < key->nentries; i++)
{
entry = key->scanEntry + i;
/*
* Get ItemPointer of next heap row to be checked from pending list.
- * Returns false if there are no more.
+ * Returns false if there are no more. On pages with several rows
+ * it returns each row separately, on page with part of heap row returns
+ * per page data. pos->firstOffset and pos->lastOffset points
+ * fraction of tuples for current heap row.
*
* The pendingBuffer is presumed pinned and share-locked on entry, and is
* pinned and share-locked on success exit. On failure exit it's released.
*/
pos->lastOffset = maxoff + 1;
}
+
+ /*
+ * Now pos->firstOffset points to the first tuple of current heap row,
+ * pos->lastOffset points to the first tuple of second heap row (or
+ * to the end of page)
+ */
+
break;
}
}
return true;
}
+/*
+ * Scan page from current tuple (off) up to the first event:
+ * - tuple's attribute number is not equal to entry's attrnum
+ * - reach of last tuple
+ * - match is found (then returns true)
+ */
static bool
matchPartialInPendingList(GinState *ginstate, Page page,
OffsetNumber off, OffsetNumber maxoff,
datumExtracted[ off-1 ] = true;
}
+ /*----------
+ * Check of partial match.
+ * case cmp == 0 => match
+ * case cmp > 0 => not match and finish scan
+ * case cmp < 0 => not match and continue scan
+ *----------
+ */
cmp = DatumGetInt32(FunctionCall4(&ginstate->comparePartialFn[attrnum],
value,
datum[off-1],
return true;
else if (cmp > 0)
return false;
+
+ off++;
}
return false;
/*
* Sets entryRes array for each key by looking at
- * every entry per indexed value (row) in pending list.
+ * every entry per indexed value (heap's row) in pending list.
* returns true if at least one of datum was matched by key's entry
*
* The pendingBuffer is presumed pinned and share-locked on entry.
StopMiddle;
GinScanEntry entry = key->scanEntry + j;
+ /* already true - do not extra work */
if ( key->entryRes[j] )
continue;
+ /*
+ * Interested tuples are from pos->firstOffset to pos->lastOffset
+ * and they are ordered by (attnum, Datum) as it's done in entry tree
+ * So we could use binary search to prevent linear scanning
+ */
while (StopLow < StopHigh)
{
StopMiddle = StopLow + ((StopHigh - StopLow) >> 1);
if ( res == 0 )
{
+ /*
+ * The exact match causes, so we just scan from
+ * current position to find a partial match.
+ * See comment above about tuple's ordering.
+ */
if ( entry->isPartialMatch )
key->entryRes[j] =
matchPartialInPendingList(&so->ginstate,
}
if ( StopLow>=StopHigh && entry->isPartialMatch )
+ {
+ /*
+ * The exact match wasn't found, so we need to start
+ * scan from first tuple greater then current entry
+ * See comment above about tuple's ordering.
+ */
key->entryRes[j] =
matchPartialInPendingList(&so->ginstate,
page, StopHigh,
datumExtracted,
entry->strategy,
entry->extra_data);
+ }
hasMatch |= key->entryRes[j];
}
{
ItemPointerData item = pos->item;
+ /*
+ * need to get next portion of tuples of row containing
+ * on several pages
+ */
+
if ( scanGetCandidate(scan, pos) == false || !ItemPointerEquals(&pos->item, &item) )
elog(ERROR,"Could not process tuple"); /* XXX should not be here ! */
}
UnlockReleaseBuffer( metabuffer );
/*
- * loop for each heap row
+ * loop for each heap row. scanGetCandidate returns full row
+ * or row's tuples from first page.
*/
while( scanGetCandidate(scan, &pos) )
{
/*
- * Check entries in rows and setup entryRes array
+ * Check entries in tuple and setup entryRes array
+ * If tuples of heap's row are placed on several pages
+ * collectDatumForItem will read all of that pages.
*/
if (!collectDatumForItem(scan, &pos))
continue;
/*
- * check for consistent
+ * Matching of entries of one row is finished,
+ * so check row by consistent function.
*/
oldCtx = MemoryContextSwitchTo(so->tempCtx);
recheck = false;
OSDN Git Service
