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Commitfd94ac5

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Fix outdated comments, GIST search queue is not an RBTree anymore.
The GiST search queue is implemented as a pairing heap rather than asRed-Black Tree, since 9.5 (commite703261). I neglected these commentsin that commit.
1 parentf65764a commitfd94ac5

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2 files changed

+9
-13
lines changed

2 files changed

+9
-13
lines changed

‎src/backend/access/gist/gistscan.c

Lines changed: 2 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -125,7 +125,7 @@ gistrescan(IndexScanDesc scan, ScanKey key, int nkeys,
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* which is created on the second call and reset on later calls. Thus, in
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* the common case where a scan is only rescan'd once, we just put the
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* queue in scanCxt and don't pay the overhead of making a second memory
128-
* context. If we do rescan more than once, the firstRBTree is just left
128+
* context. If we do rescan more than once, the firstqueue is just left
129129
* for dead until end of scan; this small wastage seems worth the savings
130130
* in the common case.
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*/
@@ -181,7 +181,7 @@ gistrescan(IndexScanDesc scan, ScanKey key, int nkeys,
181181
ALLOCSET_DEFAULT_SIZES);
182182
}
183183

184-
/* create new, emptyRBTree for search queue */
184+
/* create new, emptypairing heap for search queue */
185185
oldCxt=MemoryContextSwitchTo(so->queueCxt);
186186
so->queue=pairingheap_allocate(pairingheap_GISTSearchItem_cmp,scan);
187187
MemoryContextSwitchTo(oldCxt);

‎src/include/access/gist_private.h

Lines changed: 7 additions & 11 deletions
Original file line numberDiff line numberDiff line change
@@ -107,15 +107,11 @@ typedef struct GISTSTATE
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* upper index pages; this rule avoids doing extra work during a search that
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* ends early due to LIMIT.
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*
110-
* To perform an ordered search, we use an RBTree to manage the distance-order
111-
* queue. Each GISTSearchTreeItem stores all unvisited items of the same
112-
* distance; they are GISTSearchItems chained together via their next fields.
113-
*
114-
* In a non-ordered search (no order-by operators), the RBTree degenerates
115-
* to a single item, which we use as a queue of unvisited index pages only.
116-
* In this case matched heap items from the current index leaf page are
117-
* remembered in GISTScanOpaqueData.pageData[] and returned directly from
118-
* there, instead of building a separate GISTSearchItem for each one.
110+
* To perform an ordered search, we use a pairing heap to manage the
111+
* distance-order queue. In a non-ordered search (no order-by operators),
112+
* we use it to return heap tuples before unvisited index pages, to
113+
* ensure depth-first order, but all entries are otherwise considered
114+
* equal.
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*/
120116

121117
/* Individual heap tuple to be visited */
@@ -298,8 +294,8 @@ typedef struct
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#defineGIST_ROOT_BLKNO0
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/*
301-
* Before PostgreSQL 9.1, we used rely on so-called "invalid tuples" on inner
302-
* pages to finish crash recovery of incomplete page splits. If a crash
297+
* Before PostgreSQL 9.1, we usedtorely on so-called "invalid tuples" on
298+
*innerpages to finish crash recovery of incomplete page splits. If a crash
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* happened in the middle of a page split, so that the downlink pointers were
304300
* not yet inserted, crash recovery inserted a special downlink pointer. The
305301
* semantics of an invalid tuple was that it if you encounter one in a scan,

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