On 22.05.2012 01:09, Alexander Korotkov wrote:
Hi!
On Tue, May 22, 2012 at 12:56 AM, Heikki Linnakangas<
heikki.linnakan...@enterprisedb.com> wrote:
The management of the path stacks is a bit complicated, anyway. I'll think
about this some more tomorrow, maybe we can make it simpler, knowing that
we have to do those extra lookups.
WOW! You did enormous work on exploring that!
I just arrived from PGCon and start looking at it when find you've already
done comprehensive research of this problem.
On the step 5 if we've NSN in GISTBufferingInsertStack structure, we could
detect situation of changing parent of splitted page. Using this we could
save copy of GISTBufferingInsertStack for B2 with original parent A,
because we know split of B to occur after creating GISTBufferingInsertStack
but before split of A. The question is how to find this copy from C, hash?
I tested a patch that adds the extra getNodeBuffer() call after
refinding the parent, as discussed. However, I'm still getting a "failed
to-refind parent" error later in the build, so I think we're still
missing some corner case.
I think we should rewrite the way we track the parents completely.
Rather than keep a path stack attached to every node buffer, let's just
maintain a second hash table that contains the parent of every internal
node. Whenever a downlink is moved to another page, update the hash
table with the new information. That way we always have up-to-date
information about the parent of every internal node.
That's much easier to understand than the path stack structures we have
now. I think the overall memory consumption will be about the same too.
Although we need the extra hash table with one entry for every internal
node, we get rid of the path stack structs, which are also one per every
internal node at the moment.
I believe it is faster too. I added some instrumentation to the existing
gist code (with the additional getNodeBuffer() call added to fix this
bug), to measure the time spent moving right, when refinding the parent
of a page. I added gettimeofday() calls before and after moving right,
and summed the total. In my test case, the final index size was about
19GB, and the index build took 3545 seconds (59 minutes). Of that time,
580 seconds (~ 10 minutes) was spent moving right to refind parents.
That's a lot. I also printed a line whenever a refind operation had to
move right 20 pages or more. That happened 2482 times during the build,
in the worst case we moved right over 40000 pages.
Attached is a patch to replace the path stacks with a hash table. With
this patch, the index build time in my test case dropped from 59 minutes
to about 55 minutes. I don'αΊ— know how representative or repeatable this
test case is, but this definitely seems very worthwhile, not only
because it fixes the bug and makes the code simpler, but also on
performance grounds.
Alexander, do you still have the test environments and data lying around
that you used for GiST buffering testing last summer? Could you rerun
some of those tests with this patch?
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
diff --git a/src/backend/access/gist/gistbuild.c b/src/backend/access/gist/gistbuild.c
index 988896d..9d9a031 100644
--- a/src/backend/access/gist/gistbuild.c
+++ b/src/backend/access/gist/gistbuild.c
@@ -55,16 +55,24 @@ typedef struct
{
Relation indexrel;
GISTSTATE *giststate;
- GISTBuildBuffers *gfbb;
int64 indtuples; /* number of tuples indexed */
int64 indtuplesSize; /* total size of all indexed tuples */
Size freespace; /* amount of free space to leave on pages */
+ /*
+ * Extra data structures used during a buffering build. GISTBuildBuffers
+ * contains information related to managing the build buffers. parentMap
+ * is a lookup table of the parent of each internal page.
+ */
+ GISTBuildBuffers *gfbb;
+ HTAB *parentMap;
+
GistBufferingMode bufferingMode;
} GISTBuildState;
+/* prototypes for private functions */
static void gistInitBuffering(GISTBuildState *buildstate);
static int calculatePagesPerBuffer(GISTBuildState *buildstate, int levelStep);
static void gistBuildCallback(Relation index,
@@ -76,18 +84,23 @@ static void gistBuildCallback(Relation index,
static void gistBufferingBuildInsert(GISTBuildState *buildstate,
IndexTuple itup);
static bool gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
- GISTBufferingInsertStack *startparent);
+ BlockNumber startblkno, int startlevel);
static void gistbufferinginserttuples(GISTBuildState *buildstate,
Buffer buffer,
IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
- GISTBufferingInsertStack *path);
-static void gistBufferingFindCorrectParent(GISTBuildState *buildstate,
- GISTBufferingInsertStack *child);
+ int level, BlockNumber parent);
+static Buffer gistBufferingFindCorrectParent(GISTBuildState *buildstate,
+ BlockNumber childblkno,
+ OffsetNumber *downlinkoffnum,
+ BlockNumber *parentblkno, int level);
static void gistProcessEmptyingQueue(GISTBuildState *buildstate);
static void gistEmptyAllBuffers(GISTBuildState *buildstate);
-static void gistFreeUnreferencedPath(GISTBufferingInsertStack *path);
static int gistGetMaxLevel(Relation index);
+static void gistInitParentMap(GISTBuildState *buildstate);
+static void gistMemorizeParent(GISTBuildState *buildstate, BlockNumber child, BlockNumber parent);
+static void gistMemorizeAllDownlinks(GISTBuildState *buildstate, Buffer parent);
+static BlockNumber gistGetParent(GISTBuildState *buildstate, BlockNumber child);
/*
* Main entry point to GiST index build. Initially calls insert over and over,
@@ -392,6 +405,8 @@ gistInitBuffering(GISTBuildState *buildstate)
buildstate->gfbb = gistInitBuildBuffers(pagesPerBuffer, levelStep,
gistGetMaxLevel(index));
+ gistInitParentMap(buildstate);
+
buildstate->bufferingMode = GIST_BUFFERING_ACTIVE;
elog(DEBUG1, "switched to buffered GiST build; level step = %d, pagesPerBuffer = %d",
@@ -514,7 +529,7 @@ static void
gistBufferingBuildInsert(GISTBuildState *buildstate, IndexTuple itup)
{
/* Insert the tuple to buffers. */
- gistProcessItup(buildstate, itup, NULL);
+ gistProcessItup(buildstate, itup, 0, buildstate->gfbb->rootlevel);
/* If we filled up (half of a) buffer, process buffer emptying. */
gistProcessEmptyingQueue(buildstate);
@@ -528,30 +543,28 @@ gistBufferingBuildInsert(GISTBuildState *buildstate, IndexTuple itup)
*/
static bool
gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
- GISTBufferingInsertStack *startparent)
+ BlockNumber startblkno, int startlevel)
{
GISTSTATE *giststate = buildstate->giststate;
GISTBuildBuffers *gfbb = buildstate->gfbb;
Relation indexrel = buildstate->indexrel;
- GISTBufferingInsertStack *path;
BlockNumber childblkno;
Buffer buffer;
bool result = false;
+ BlockNumber blkno;
+ int level;
+ OffsetNumber downlinkoffnum;
+ BlockNumber parentblkno = InvalidBlockNumber;
- /*
- * NULL passed in startparent means that we start index tuple processing
- * from the root.
- */
- if (!startparent)
- path = gfbb->rootitem;
- else
- path = startparent;
+ CHECK_FOR_INTERRUPTS();
/*
* Loop until we reach a leaf page (level == 0) or a level with buffers
* (not including the level we start at, because we would otherwise make
* no progress).
*/
+ blkno = startblkno;
+ level = startlevel;
for (;;)
{
ItemId iid;
@@ -559,21 +572,21 @@ gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
newtup;
Page page;
OffsetNumber childoffnum;
- GISTBufferingInsertStack *parent;
/* Have we reached a level with buffers? */
- if (LEVEL_HAS_BUFFERS(path->level, gfbb) && path != startparent)
+ if (LEVEL_HAS_BUFFERS(level, gfbb) && level != startlevel)
break;
/* Have we reached a leaf page? */
- if (path->level == 0)
+ if (level == 0)
break;
/*
* Nope. Descend down to the next level then. Choose a child to
* descend down to.
*/
- buffer = ReadBuffer(indexrel, path->blkno);
+
+ buffer = ReadBuffer(indexrel, blkno);
LockBuffer(buffer, GIST_EXCLUSIVE);
page = (Page) BufferGetPage(buffer);
@@ -582,32 +595,32 @@ gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
idxtuple = (IndexTuple) PageGetItem(page, iid);
childblkno = ItemPointerGetBlockNumber(&(idxtuple->t_tid));
+ if (level > 1)
+ gistMemorizeParent(buildstate, childblkno, blkno);
+
/*
* Check that the key representing the target child node is consistent
* with the key we're inserting. Update it if it's not.
*/
newtup = gistgetadjusted(indexrel, idxtuple, itup, giststate);
if (newtup)
+ {
gistbufferinginserttuples(buildstate, buffer, &newtup, 1,
- childoffnum, path);
- UnlockReleaseBuffer(buffer);
+ childoffnum, level, InvalidBlockNumber);
+ /* gistbufferinginserttuples() released the buffer */
+ }
+ else
+ UnlockReleaseBuffer(buffer);
- /* Create new path item representing current page */
- parent = path;
- path = (GISTBufferingInsertStack *) MemoryContextAlloc(gfbb->context,
- sizeof(GISTBufferingInsertStack));
- path->parent = parent;
- path->level = parent->level - 1;
- path->blkno = childblkno;
- path->downlinkoffnum = childoffnum;
- path->refCount = 0; /* it's unreferenced for now */
-
- /* Adjust reference count of parent */
- if (parent)
- parent->refCount++;
+ /* Descend to the child */
+ parentblkno = blkno;
+ blkno = childblkno;
+ downlinkoffnum = childoffnum;
+ Assert(level > 0);
+ level--;
}
- if (LEVEL_HAS_BUFFERS(path->level, gfbb))
+ if (LEVEL_HAS_BUFFERS(level, gfbb))
{
/*
* We've reached level with buffers. Place the index tuple to the
@@ -616,8 +629,7 @@ gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
GISTNodeBuffer *childNodeBuffer;
/* Find the buffer or create a new one */
- childNodeBuffer = gistGetNodeBuffer(gfbb, giststate, path->blkno,
- path->downlinkoffnum, path->parent);
+ childNodeBuffer = gistGetNodeBuffer(gfbb, giststate, blkno, level);
/* Add index tuple to it */
gistPushItupToNodeBuffer(gfbb, childNodeBuffer, itup);
@@ -630,19 +642,16 @@ gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
/*
* We've reached a leaf page. Place the tuple here.
*/
- buffer = ReadBuffer(indexrel, path->blkno);
+ Assert(level == 0);
+ buffer = ReadBuffer(indexrel, blkno);
LockBuffer(buffer, GIST_EXCLUSIVE);
gistbufferinginserttuples(buildstate, buffer, &itup, 1,
- InvalidOffsetNumber, path);
- UnlockReleaseBuffer(buffer);
+ InvalidOffsetNumber, level, parentblkno);
+ /* TODO: we should pass the downlink offnum, to avoid having to scan
+ * the whole parent page to find the downlink */
+ /* gistbufferinginserttuples() released the buffer */
}
- /*
- * Free unreferenced path items, if any. Path item may be referenced by
- * node buffer.
- */
- gistFreeUnreferencedPath(path);
-
return result;
}
@@ -650,11 +659,14 @@ gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
* Insert tuples to a given page.
*
* This is analogous with gistinserttuples() in the regular insertion code.
+ *
+ * Caller should hold a lock on 'buffer' on entry. This function will unlock
+ * and unpin it.
*/
static void
gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer,
IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
- GISTBufferingInsertStack *path)
+ int level, BlockNumber parentblkno)
{
GISTBuildBuffers *gfbb = buildstate->gfbb;
List *splitinfo;
@@ -677,33 +689,40 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer,
*/
if (is_split && BufferGetBlockNumber(buffer) == GIST_ROOT_BLKNO)
{
- GISTBufferingInsertStack *oldroot = gfbb->rootitem;
Page page = BufferGetPage(buffer);
- ItemId iid;
- IndexTuple idxtuple;
- BlockNumber leftmostchild;
+ OffsetNumber off;
+ OffsetNumber maxoff;
+
+ Assert(level == gfbb->rootlevel);
+ gfbb->rootlevel++;
- gfbb->rootitem = (GISTBufferingInsertStack *) MemoryContextAlloc(
- gfbb->context, sizeof(GISTBufferingInsertStack));
- gfbb->rootitem->parent = NULL;
- gfbb->rootitem->blkno = GIST_ROOT_BLKNO;
- gfbb->rootitem->downlinkoffnum = InvalidOffsetNumber;
- gfbb->rootitem->level = oldroot->level + 1;
- gfbb->rootitem->refCount = 1;
+ elog(DEBUG1, "splitting GiST root page, now %d levels deep", gfbb->rootlevel);
/*
* All the downlinks on the old root page are now on one of the child
- * pages. Change the block number of the old root entry in the stack
- * to point to the leftmost child. The other child pages will be
- * accessible from there by walking right.
+ * pages. Visit all the new child pages to memorize the parents of
+ * the grandchildren.
*/
- iid = PageGetItemId(page, FirstOffsetNumber);
- idxtuple = (IndexTuple) PageGetItem(page, iid);
- leftmostchild = ItemPointerGetBlockNumber(&(idxtuple->t_tid));
+ if (gfbb->rootlevel > 1)
+ {
+ maxoff = PageGetMaxOffsetNumber(page);
+ for (off = FirstOffsetNumber; off <= maxoff; off++)
+ {
+ ItemId iid = PageGetItemId(page, FirstOffsetNumber);
+ IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
+ BlockNumber childblkno = ItemPointerGetBlockNumber(&(idxtuple->t_tid));
+ Buffer childbuf = ReadBuffer(buildstate->indexrel, childblkno);
+ LockBuffer(childbuf, GIST_SHARE);
+ gistMemorizeAllDownlinks(buildstate, childbuf);
+ UnlockReleaseBuffer(childbuf);
- oldroot->parent = gfbb->rootitem;
- oldroot->blkno = leftmostchild;
- oldroot->downlinkoffnum = InvalidOffsetNumber;
+ /*
+ * Also remember that the parent of the new child page is
+ * the root block.
+ */
+ gistMemorizeParent(buildstate, childblkno, GIST_ROOT_BLKNO);
+ }
+ }
}
if (splitinfo)
@@ -711,16 +730,22 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer,
/*
* Insert the downlinks to the parent. This is analogous with
* gistfinishsplit() in the regular insertion code, but the locking is
- * simpler, and we have to maintain the buffers.
+ * simpler, and we have to maintain the buffers on internal nodes and
+ * the parent map.
*/
IndexTuple *downlinks;
int ndownlinks,
i;
Buffer parentBuffer;
ListCell *lc;
+ OffsetNumber downlinkoffnum = InvalidOffsetNumber;
/* Parent may have changed since we memorized this path. */
- gistBufferingFindCorrectParent(buildstate, path);
+ parentBuffer = gistBufferingFindCorrectParent(buildstate,
+ BufferGetBlockNumber(buffer),
+ &downlinkoffnum,
+ &parentblkno,
+ level);
/*
* If there's a buffer associated with this page, that needs to be
@@ -732,7 +757,8 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer,
gistRelocateBuildBuffersOnSplit(gfbb,
buildstate->giststate,
buildstate->indexrel,
- path, buffer, splitinfo);
+ level,
+ buffer, splitinfo);
/* Create an array of all the downlink tuples */
ndownlinks = list_length(splitinfo);
@@ -743,124 +769,115 @@ gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer,
GISTPageSplitInfo *splitinfo = lfirst(lc);
/*
+ * Remember the parent of each new child page in our parent map.
+ * This assumes that the downlinks fit on the parent page. If the
+ * parent page is split, too, when we recurse up to insert the
+ * downlinks, the recursive gistbufferinginserttuples() call
+ * will update the map again.
+ */
+ if (level > 0)
+ gistMemorizeParent(buildstate,
+ BufferGetBlockNumber(splitinfo->buf),
+ BufferGetBlockNumber(parentBuffer));
+
+ /*
+ * Also update the parent map for all the downlinks that got moved
+ * to a different page. (actually this also loops through the
+ * downlinks that stayed on the original page, but it does no
+ * harm).
+ */
+ if (level > 1)
+ gistMemorizeAllDownlinks(buildstate, splitinfo->buf);
+
+ /*
* Since there's no concurrent access, we can release the lower
- * level buffers immediately. Don't release the buffer for the
- * original page, though, because the caller will release that.
+ * level buffers immediately. This includes the original page.
*/
- if (splitinfo->buf != buffer)
- UnlockReleaseBuffer(splitinfo->buf);
+ UnlockReleaseBuffer(splitinfo->buf);
downlinks[i++] = splitinfo->downlink;
}
/* Insert them into parent. */
- parentBuffer = ReadBuffer(buildstate->indexrel, path->parent->blkno);
- LockBuffer(parentBuffer, GIST_EXCLUSIVE);
gistbufferinginserttuples(buildstate, parentBuffer,
downlinks, ndownlinks,
- path->downlinkoffnum, path->parent);
- UnlockReleaseBuffer(parentBuffer);
+ downlinkoffnum, level + 1, InvalidBlockNumber);
list_free_deep(splitinfo); /* we don't need this anymore */
}
+ else
+ UnlockReleaseBuffer(buffer);
}
/*
* Find correct parent by following rightlinks in buffering index build. This
* method of parent searching is possible because no concurrent activity is
* possible while index builds.
+ *
+ * Returns a buffer containing the parent page, exclusively-locked.
+ * *downlinkoffnum and *parentblkno are set to point to the downlink.
*/
-static void
+static Buffer
gistBufferingFindCorrectParent(GISTBuildState *buildstate,
- GISTBufferingInsertStack *child)
+ BlockNumber childblkno,
+ OffsetNumber *downlinkoffnum,
+ BlockNumber *parentblkno,
+ int level)
{
- GISTBuildBuffers *gfbb = buildstate->gfbb;
- Relation indexrel = buildstate->indexrel;
- GISTBufferingInsertStack *parent = child->parent;
- OffsetNumber i,
- maxoff;
- ItemId iid;
- IndexTuple idxtuple;
+ BlockNumber parent;
Buffer buffer;
Page page;
- bool copied = false;
+ OffsetNumber maxoff;
+ OffsetNumber off;
+
+ if (level > 0)
+ parent = gistGetParent(buildstate, childblkno);
+ else
+ {
+ if (*parentblkno == InvalidBlockNumber)
+ elog(ERROR, "no parent buffer provided of child %d", childblkno);
+ parent = *parentblkno;
+ }
- buffer = ReadBuffer(indexrel, parent->blkno);
+ buffer = ReadBuffer(buildstate->indexrel, parent);
page = BufferGetPage(buffer);
LockBuffer(buffer, GIST_EXCLUSIVE);
- gistcheckpage(indexrel, buffer);
+ gistcheckpage(buildstate->indexrel, buffer);
+ maxoff = PageGetMaxOffsetNumber(page);
/* Check if it was not moved */
- if (child->downlinkoffnum != InvalidOffsetNumber &&
- child->downlinkoffnum <= PageGetMaxOffsetNumber(page))
+ if (parent == *parentblkno && *parentblkno != InvalidBlockNumber &&
+ *downlinkoffnum != InvalidOffsetNumber && *downlinkoffnum <= maxoff)
{
- iid = PageGetItemId(page, child->downlinkoffnum);
- idxtuple = (IndexTuple) PageGetItem(page, iid);
- if (ItemPointerGetBlockNumber(&(idxtuple->t_tid)) == child->blkno)
+ ItemId iid = PageGetItemId(page, *downlinkoffnum);
+ IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
+ if (ItemPointerGetBlockNumber(&(idxtuple->t_tid)) == childblkno)
{
/* Still there */
- UnlockReleaseBuffer(buffer);
- return;
+ return buffer;
}
}
- /* parent has changed, look child in right links until found */
- while (true)
+ /*
+ * Downlink was not at the offset where it used to be. Scan the page
+ * to find it. During normal gist insertions, it might've moved to another
+ * page, to the right, but during a buffering build, we keep track of
+ * the parent of each page in the lookup table so we should always know
+ * what page it's on.
+ */
+ for (off = FirstOffsetNumber; off <= maxoff; off = OffsetNumberNext(off))
{
- /* Search for relevant downlink in the current page */
- maxoff = PageGetMaxOffsetNumber(page);
- for (i = FirstOffsetNumber; i <= maxoff; i = OffsetNumberNext(i))
+ ItemId iid = PageGetItemId(page, off);
+ IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
+ if (ItemPointerGetBlockNumber(&(idxtuple->t_tid)) == childblkno)
{
- iid = PageGetItemId(page, i);
- idxtuple = (IndexTuple) PageGetItem(page, iid);
- if (ItemPointerGetBlockNumber(&(idxtuple->t_tid)) == child->blkno)
- {
- /* yes!!, found */
- child->downlinkoffnum = i;
- UnlockReleaseBuffer(buffer);
- return;
- }
+ /* yes!!, found it */
+ *downlinkoffnum = off;
+ return buffer;
}
-
- /*
- * We should copy parent path item because some other path items can
- * refer to it.
- */
- if (!copied)
- {
- parent = (GISTBufferingInsertStack *) MemoryContextAlloc(gfbb->context,
- sizeof(GISTBufferingInsertStack));
- memcpy(parent, child->parent, sizeof(GISTBufferingInsertStack));
- if (parent->parent)
- parent->parent->refCount++;
- gistDecreasePathRefcount(child->parent);
- child->parent = parent;
- parent->refCount = 1;
- copied = true;
- }
-
- /*
- * Not found in current page. Move towards rightlink.
- */
- parent->blkno = GistPageGetOpaque(page)->rightlink;
- UnlockReleaseBuffer(buffer);
-
- if (parent->blkno == InvalidBlockNumber)
- {
- /*
- * End of chain and still didn't find parent. Should not happen
- * during index build.
- */
- break;
- }
-
- /* Get the next page */
- buffer = ReadBuffer(indexrel, parent->blkno);
- page = BufferGetPage(buffer);
- LockBuffer(buffer, GIST_EXCLUSIVE);
- gistcheckpage(indexrel, buffer);
}
- elog(ERROR, "failed to re-find parent for block %u", child->blkno);
+ elog(ERROR, "failed to re-find parent for block %u", childblkno);
+ return InvalidBuffer; /* keep compiler quiet */
}
/*
@@ -919,7 +936,7 @@ gistProcessEmptyingQueue(GISTBuildState *buildstate)
* threshold, but we might as well keep flushing tuples from it
* until we fill a lower-level buffer.
*/
- if (gistProcessItup(buildstate, itup, emptyingNodeBuffer->path))
+ if (gistProcessItup(buildstate, itup, emptyingNodeBuffer->nodeBlocknum, emptyingNodeBuffer->level))
{
/*
* A lower level buffer filled up. Stop emptying this buffer,
@@ -988,46 +1005,12 @@ gistEmptyAllBuffers(GISTBuildState *buildstate)
gfbb->buffersOnLevels[i] =
list_delete_first(gfbb->buffersOnLevels[i]);
}
+ elog(DEBUG2, "emptied all buffers at level %d", i);
}
MemoryContextSwitchTo(oldCtx);
}
/*
- * Free unreferenced parts of a path stack.
- */
-static void
-gistFreeUnreferencedPath(GISTBufferingInsertStack *path)
-{
- while (path->refCount == 0)
- {
- /*
- * Path part is unreferenced. We can free it and decrease reference
- * count of parent. If parent becomes unreferenced too procedure
- * should be repeated for it.
- */
- GISTBufferingInsertStack *tmp = path->parent;
-
- pfree(path);
- path = tmp;
- if (path)
- path->refCount--;
- else
- break;
- }
-}
-
-/*
- * Decrease reference count of a path part, and free any unreferenced parts of
- * the path stack.
- */
-void
-gistDecreasePathRefcount(GISTBufferingInsertStack *path)
-{
- path->refCount--;
- gistFreeUnreferencedPath(path);
-}
-
-/*
* Get the depth of the GiST index.
*/
static int
@@ -1076,9 +1059,112 @@ gistGetMaxLevel(Relation index)
/*
* We're going down on the tree. It means that there is yet one more
- * level is the tree.
+ * level in the tree.
*/
maxLevel++;
}
return maxLevel;
}
+
+
+/*
+ * Routines for managing the parent map.
+ *
+ * Whenever a page is split, we need to insert the downlinks into the parent.
+ * We need to somehow find the parent page to do that. In normal insertions,
+ * we keep a stack of nodes visited when we descend the tree. However, in
+ * buffering build, we can start descending the tree from any internal node,
+ * when we empty a buffer by cascading tuples to its children. So we don't
+ * have a full stack up to the root available at that time.
+ *
+ * So instead, we maintain a hash table to track the parent of every internal
+ * page. We don't need to track the parents of leaf nodes, however. Whenever
+ * we insert to a leaf, we've just descended down from its parent, so we know
+ * its immediate parent already. This helps a lot to limit the memory used
+ * by this hash table.
+ *
+ * Whenever an internal node is split, the parent map needs to be updated.
+ * the parent of the new child page needs to be recorded, and also the
+ * entries for all page whose downlinks are moved to a new page at the split
+ * needs to be updated.
+ *
+ * We also update the parent map whenever we descend the tree. That might seem
+ * unnecessary, because we maintain the map whenever a downlink is moved or
+ * created, but it is needed because we switch to buffering mode after
+ * creating a tree with regular index inserts. Any pages created before
+ * switching to buffering mode will not be present in the parent map initially,
+ * but will be added there the first time we visit them.
+ */
+
+typedef struct
+{
+ BlockNumber childblkno; /* hash key */
+ BlockNumber parentblkno;
+ int childlevel;
+} ParentMapEntry;
+
+static void
+gistInitParentMap(GISTBuildState *buildstate)
+{
+ HASHCTL hashCtl;
+
+ hashCtl.keysize = sizeof(BlockNumber);
+ hashCtl.entrysize = sizeof(ParentMapEntry);
+ hashCtl.hcxt = CurrentMemoryContext;
+ hashCtl.hash = oid_hash;
+ buildstate->parentMap = hash_create("gistbuild parent map",
+ 1024,
+ &hashCtl,
+ HASH_ELEM | HASH_CONTEXT
+ | HASH_FUNCTION);
+}
+
+static void
+gistMemorizeParent(GISTBuildState *buildstate, BlockNumber child, BlockNumber parent)
+{
+ ParentMapEntry *entry;
+ bool found;
+
+ entry = (ParentMapEntry *) hash_search(buildstate->parentMap,
+ (const void *) &child,
+ HASH_ENTER,
+ &found);
+ entry->parentblkno = parent;
+}
+
+static void
+gistMemorizeAllDownlinks(GISTBuildState *buildstate, Buffer parentbuf)
+{
+ OffsetNumber maxoff;
+ OffsetNumber off;
+ BlockNumber parentblkno = BufferGetBlockNumber(parentbuf);
+ Page page = BufferGetPage(parentbuf);
+
+ Assert(!GistPageIsLeaf(page));
+
+ maxoff = PageGetMaxOffsetNumber(page);
+ for (off = FirstOffsetNumber; off <= maxoff; off++)
+ {
+ ItemId iid = PageGetItemId(page, off);
+ IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
+ BlockNumber childblkno = ItemPointerGetBlockNumber(&(idxtuple->t_tid));
+ gistMemorizeParent(buildstate, childblkno, parentblkno);
+ }
+}
+
+static BlockNumber
+gistGetParent(GISTBuildState *buildstate, BlockNumber child)
+{
+ ParentMapEntry *entry;
+ bool found;
+
+ /* Find node buffer in hash table */
+ entry = (ParentMapEntry *) hash_search(buildstate->parentMap,
+ (const void *) &child,
+ HASH_FIND,
+ &found);
+ if (!found)
+ elog(ERROR, "could not find parent of block %d in lookup table", child);
+
+ return entry->parentblkno;
+}
diff --git a/src/backend/access/gist/gistbuildbuffers.c b/src/backend/access/gist/gistbuildbuffers.c
index a40b838..211ad21 100644
--- a/src/backend/access/gist/gistbuildbuffers.c
+++ b/src/backend/access/gist/gistbuildbuffers.c
@@ -107,16 +107,7 @@ gistInitBuildBuffers(int pagesPerBuffer, int levelStep, int maxLevel)
sizeof(GISTNodeBuffer *));
gfbb->loadedBuffersCount = 0;
- /*
- * Root path item of the tree. Updated on each root node split.
- */
- gfbb->rootitem = (GISTBufferingInsertStack *) MemoryContextAlloc(
- gfbb->context, sizeof(GISTBufferingInsertStack));
- gfbb->rootitem->parent = NULL;
- gfbb->rootitem->blkno = GIST_ROOT_BLKNO;
- gfbb->rootitem->downlinkoffnum = InvalidOffsetNumber;
- gfbb->rootitem->level = maxLevel;
- gfbb->rootitem->refCount = 1;
+ gfbb->rootlevel = maxLevel;
return gfbb;
}
@@ -127,9 +118,7 @@ gistInitBuildBuffers(int pagesPerBuffer, int levelStep, int maxLevel)
*/
GISTNodeBuffer *
gistGetNodeBuffer(GISTBuildBuffers *gfbb, GISTSTATE *giststate,
- BlockNumber nodeBlocknum,
- OffsetNumber downlinkoffnum,
- GISTBufferingInsertStack *parent)
+ BlockNumber nodeBlocknum, int level)
{
GISTNodeBuffer *nodeBuffer;
bool found;
@@ -144,8 +133,6 @@ gistGetNodeBuffer(GISTBuildBuffers *gfbb, GISTSTATE *giststate,
/*
* Node buffer wasn't found. Initialize the new buffer as empty.
*/
- GISTBufferingInsertStack *path;
- int level;
MemoryContext oldcxt = MemoryContextSwitchTo(gfbb->context);
/* nodeBuffer->nodeBlocknum is the hash key and was filled in already */
@@ -153,33 +140,12 @@ gistGetNodeBuffer(GISTBuildBuffers *gfbb, GISTSTATE *giststate,
nodeBuffer->pageBlocknum = InvalidBlockNumber;
nodeBuffer->pageBuffer = NULL;
nodeBuffer->queuedForEmptying = false;
-
- /*
- * Create a path stack for the page.
- */
- if (nodeBlocknum != GIST_ROOT_BLKNO)
- {
- path = (GISTBufferingInsertStack *) palloc(
- sizeof(GISTBufferingInsertStack));
- path->parent = parent;
- path->blkno = nodeBlocknum;
- path->downlinkoffnum = downlinkoffnum;
- path->level = parent->level - 1;
- path->refCount = 0; /* initially unreferenced */
- parent->refCount++; /* this path references its parent */
- Assert(path->level > 0);
- }
- else
- path = gfbb->rootitem;
-
- nodeBuffer->path = path;
- path->refCount++;
+ nodeBuffer->level = level;
/*
* Add this buffer to the list of buffers on this level. Enlarge
* buffersOnLevels array if needed.
*/
- level = path->level;
if (level >= gfbb->buffersOnLevelsLen)
{
int i;
@@ -210,20 +176,6 @@ gistGetNodeBuffer(GISTBuildBuffers *gfbb, GISTSTATE *giststate,
MemoryContextSwitchTo(oldcxt);
}
- else
- {
- if (parent != nodeBuffer->path->parent)
- {
- /*
- * A different parent path item was provided than we've
- * remembered. We trust caller to provide more correct parent than
- * we have. Previous parent may be outdated by page split.
- */
- gistDecreasePathRefcount(nodeBuffer->path->parent);
- nodeBuffer->path->parent = parent;
- parent->refCount++;
- }
- }
return nodeBuffer;
}
@@ -585,7 +537,7 @@ typedef struct
*/
void
gistRelocateBuildBuffersOnSplit(GISTBuildBuffers *gfbb, GISTSTATE *giststate,
- Relation r, GISTBufferingInsertStack *path,
+ Relation r, int level,
Buffer buffer, List *splitinfo)
{
RelocationBufferInfo *relocationBuffersInfos;
@@ -601,7 +553,7 @@ gistRelocateBuildBuffersOnSplit(GISTBuildBuffers *gfbb, GISTSTATE *giststate,
ListCell *lc;
/* If the splitted page doesn't have buffers, we have nothing to do. */
- if (!LEVEL_HAS_BUFFERS(path->level, gfbb))
+ if (!LEVEL_HAS_BUFFERS(level, gfbb))
return;
/*
@@ -660,14 +612,11 @@ gistRelocateBuildBuffersOnSplit(GISTBuildBuffers *gfbb, GISTSTATE *giststate,
/*
* Create a node buffer for the page. The leftmost half is on the same
* block as the old page before split, so for the leftmost half this
- * will return the original buffer, which was emptied earlier in this
- * function.
+ * will return the original buffer. The tuples on the original buffer
+ * were relinked to the temporary buffer, so the original one is now
+ * empty.
*/
- newNodeBuffer = gistGetNodeBuffer(gfbb,
- giststate,
- BufferGetBlockNumber(si->buf),
- path->downlinkoffnum,
- path->parent);
+ newNodeBuffer = gistGetNodeBuffer(gfbb, giststate, BufferGetBlockNumber(si->buf), level);
relocationBuffersInfos[i].nodeBuffer = newNodeBuffer;
relocationBuffersInfos[i].splitinfo = si;
diff --git a/src/include/access/gist_private.h b/src/include/access/gist_private.h
index 481ef5f..5ad9858 100644
--- a/src/include/access/gist_private.h
+++ b/src/include/access/gist_private.h
@@ -329,7 +329,7 @@ typedef struct
/* is this a temporary copy, not in the hash table? */
bool isTemp;
- struct GISTBufferingInsertStack *path;
+ int level; /* 0 == leaf */
} GISTNodeBuffer;
/*
@@ -338,7 +338,7 @@ typedef struct
*/
#define LEVEL_HAS_BUFFERS(nlevel, gfbb) \
((nlevel) != 0 && (nlevel) % (gfbb)->levelStep == 0 && \
- (nlevel) != (gfbb)->rootitem->level)
+ (nlevel) != (gfbb)->rootlevel)
/* Is specified buffer at least half-filled (should be queued for emptying)? */
#define BUFFER_HALF_FILLED(nodeBuffer, gfbb) \
@@ -353,26 +353,6 @@ typedef struct
((nodeBuffer)->blocksCount > (gfbb)->pagesPerBuffer)
/*
- * Extended GISTInsertStack for buffering GiST index build.
- */
-typedef struct GISTBufferingInsertStack
-{
- /* current page */
- BlockNumber blkno;
-
- /* offset of the downlink in the parent page, that points to this page */
- OffsetNumber downlinkoffnum;
-
- /* pointer to parent */
- struct GISTBufferingInsertStack *parent;
-
- int refCount;
-
- /* level number */
- int level;
-} GISTBufferingInsertStack;
-
-/*
* Data structure with general information about build buffers.
*/
typedef struct GISTBuildBuffers
@@ -416,8 +396,8 @@ typedef struct GISTBuildBuffers
int loadedBuffersCount; /* # of entries in loadedBuffers */
int loadedBuffersLen; /* allocated size of loadedBuffers */
- /* A path item that points to the current root node */
- GISTBufferingInsertStack *rootitem;
+ /* Level of the current root node (= height of the index tree - 1) */
+ int rootlevel;
} GISTBuildBuffers;
/*
@@ -551,15 +531,13 @@ extern void gistSplitByKey(Relation r, Page page, IndexTuple *itup,
/* gistbuild.c */
extern Datum gistbuild(PG_FUNCTION_ARGS);
extern void gistValidateBufferingOption(char *value);
-extern void gistDecreasePathRefcount(GISTBufferingInsertStack *path);
/* gistbuildbuffers.c */
extern GISTBuildBuffers *gistInitBuildBuffers(int pagesPerBuffer, int levelStep,
int maxLevel);
extern GISTNodeBuffer *gistGetNodeBuffer(GISTBuildBuffers *gfbb,
GISTSTATE *giststate,
- BlockNumber blkno, OffsetNumber downlinkoffnum,
- GISTBufferingInsertStack *parent);
+ BlockNumber blkno, int level);
extern void gistPushItupToNodeBuffer(GISTBuildBuffers *gfbb,
GISTNodeBuffer *nodeBuffer, IndexTuple item);
extern bool gistPopItupFromNodeBuffer(GISTBuildBuffers *gfbb,
@@ -567,7 +545,7 @@ extern bool gistPopItupFromNodeBuffer(GISTBuildBuffers *gfbb,
extern void gistFreeBuildBuffers(GISTBuildBuffers *gfbb);
extern void gistRelocateBuildBuffersOnSplit(GISTBuildBuffers *gfbb,
GISTSTATE *giststate, Relation r,
- GISTBufferingInsertStack *path, Buffer buffer,
+ int level, Buffer buffer,
List *splitinfo);
extern void gistUnloadNodeBuffers(GISTBuildBuffers *gfbb);
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
