/*-------------------------------------------------------------------------
*
* gistbuild.c
* build algorithm for GiST indexes implementation.
*
*
* Portions Copyright (c) 1996-2017, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/access/gist/gistbuild.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include <math.h>
#include "access/genam.h"
#include "access/gist_private.h"
#include "access/gistxlog.h"
#include "access/xloginsert.h"
#include "catalog/index.h"
#include "miscadmin.h"
#include "optimizer/cost.h"
#include "storage/bufmgr.h"
#include "storage/smgr.h"
#include "utils/memutils.h"
#include "utils/rel.h"
/* Step of index tuples for check whether to switch to buffering build mode */
#define BUFFERING_MODE_SWITCH_CHECK_STEP 256
/*
* Number of tuples to process in the slow way before switching to buffering
* mode, when buffering is explicitly turned on. Also, the number of tuples
* to process between readjusting the buffer size parameter, while in
* buffering mode.
*/
#define BUFFERING_MODE_TUPLE_SIZE_STATS_TARGET 4096
typedef enum
{
GIST_BUFFERING_DISABLED, /* in regular build mode and aren't going to
* switch */
GIST_BUFFERING_AUTO, /* in regular build mode, but will switch to
* buffering build mode if the index grows too
* big */
GIST_BUFFERING_STATS, /* gathering statistics of index tuple size
* before switching to the buffering build
* mode */
GIST_BUFFERING_ACTIVE /* in buffering build mode */
} GistBufferingMode;
/* Working state for gistbuild and its callback */
typedef struct
{
Relation indexrel;
Relation heaprel;
GISTSTATE *giststate;
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. 'gfbb' 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,
HeapTuple htup,
Datum *values,
bool *isnull,
bool tupleIsAlive,
void *state);
static void gistBufferingBuildInsert(GISTBuildState *buildstate,
IndexTuple itup);
static bool gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
BlockNumber startblkno, int startlevel);
static BlockNumber gistbufferinginserttuples(GISTBuildState *buildstate,
Buffer buffer, int level,
IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
BlockNumber parentblk, OffsetNumber downlinkoffnum);
static Buffer gistBufferingFindCorrectParent(GISTBuildState *buildstate,
BlockNumber childblkno, int level,
BlockNumber *parentblk,
OffsetNumber *downlinkoffnum);
static void gistProcessEmptyingQueue(GISTBuildState *buildstate);
static void gistEmptyAllBuffers(GISTBuildState *buildstate);
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,
* but switches to more efficient buffering build algorithm after a certain
* number of tuples (unless buffering mode is disabled).
*/
IndexBuildResult *
gistbuild(Relation heap, Relation index, IndexInfo *indexInfo)
{
IndexBuildResult *result;
double reltuples;
GISTBuildState buildstate;
Buffer buffer;
Page page;
MemoryContext oldcxt = CurrentMemoryContext;
int fillfactor;
buildstate.indexrel = index;
buildstate.heaprel = heap;
if (index->rd_options)
{
/* Get buffering mode from the options string */
GiSTOptions *options = (GiSTOptions *) index->rd_options;
char *bufferingMode = (char *) options + options->bufferingModeOffset;
if (strcmp(bufferingMode, "on") == 0)
buildstate.bufferingMode = GIST_BUFFERING_STATS;
else if (strcmp(bufferingMode, "off") == 0)
buildstate.bufferingMode = GIST_BUFFERING_DISABLED;
else
buildstate.bufferingMode = GIST_BUFFERING_AUTO;
fillfactor = options->fillfactor;
}
else
{
/*
* By default, switch to buffering mode when the index grows too large
* to fit in cache.
*/
buildstate.bufferingMode = GIST_BUFFERING_AUTO;
fillfactor = GIST_DEFAULT_FILLFACTOR;
}
/* Calculate target amount of free space to leave on pages */
buildstate.freespace = BLCKSZ * (100 - fillfactor) / 100;
/*
* We expect to be called exactly once for any index relation. If that's
* not the case, big trouble's what we have.
*/
if (RelationGetNumberOfBlocks(index) != 0)
elog(ERROR, "index \"%s\" already contains data",
RelationGetRelationName(index));
/* no locking is needed */
buildstate.giststate = initGISTstate(index);
/*
* Create a temporary memory context that is reset once for each tuple
* processed. (Note: we don't bother to make this a child of the
* giststate's scanCxt, so we have to delete it separately at the end.)
*/
buildstate.giststate->tempCxt = createTempGistContext();
/* initialize the root page */
buffer = gistNewBuffer(index);
Assert(BufferGetBlockNumber(buffer) == GIST_ROOT_BLKNO);
page = BufferGetPage(buffer);
START_CRIT_SECTION();
GISTInitBuffer(buffer, F_LEAF);
MarkBufferDirty(buffer);
if (RelationNeedsWAL(index))
{
XLogRecPtr recptr;
XLogBeginInsert();
XLogRegisterBuffer(0, buffer, REGBUF_WILL_INIT);
recptr = XLogInsert(RM_GIST_ID, XLOG_GIST_CREATE_INDEX);
PageSetLSN(page, recptr);
}
else
PageSetLSN(page, gistGetFakeLSN(heap));
UnlockReleaseBuffer(buffer);
END_CRIT_SECTION();
/* build the index */
buildstate.indtuples = 0;
buildstate.indtuplesSize = 0;
/*
* Do the heap scan.
*/
reltuples = IndexBuildHeapScan(heap, index, indexInfo, true,
gistBuildCallback, (void *) &buildstate);
/*
* If buffering was used, flush out all the tuples that are still in the
* buffers.
*/
if (buildstate.bufferingMode == GIST_BUFFERING_ACTIVE)
{
elog(DEBUG1, "all tuples processed, emptying buffers");
gistEmptyAllBuffers(&buildstate);
gistFreeBuildBuffers(buildstate.gfbb);
}
/* okay, all heap tuples are indexed */
MemoryContextSwitchTo(oldcxt);
MemoryContextDelete(buildstate.giststate->tempCxt);
freeGISTstate(buildstate.giststate);
/*
* Return statistics
*/
result = (IndexBuildResult *) palloc(sizeof(IndexBuildResult));
result->heap_tuples = reltuples;
result->index_tuples = (double) buildstate.indtuples;
return result;
}
/*
* Validator for "buffering" reloption on GiST indexes. Allows "on", "off"
* and "auto" values.
*/
void
gistValidateBufferingOption(char *value)
{
if (value == NULL ||
(strcmp(value, "on") != 0 &&
strcmp(value, "off") != 0 &&
strcmp(value, "auto") != 0))
{
ereport(ERROR,
(errcode(ERRCODE_INVALID_PARAMETER_VALUE),
errmsg("invalid value for \"buffering\" option"),
errdetail("Valid values are \"on\", \"off\", and \"auto\".")));
}
}
/*
* Attempt to switch to buffering mode.
*
* If there is not enough memory for buffering build, sets bufferingMode
* to GIST_BUFFERING_DISABLED, so that we don't bother to try the switch
* anymore. Otherwise initializes the build buffers, and sets bufferingMode to
* GIST_BUFFERING_ACTIVE.
*/
static void
gistInitBuffering(GISTBuildState *buildstate)
{
Relation index = buildstate->indexrel;
int pagesPerBuffer;
Size pageFreeSpace;
Size itupAvgSize,
itupMinSize;
double avgIndexTuplesPerPage,
maxIndexTuplesPerPage;
int i;
int levelStep;
/* Calc space of index page which is available for index tuples */
pageFreeSpace = BLCKSZ - SizeOfPageHeaderData - sizeof(GISTPageOpaqueData)
- sizeof(ItemIdData)
- buildstate->freespace;
/*
* Calculate average size of already inserted index tuples using gathered
* statistics.
*/
itupAvgSize = (double) buildstate->indtuplesSize /
(double) buildstate->indtuples;
/*
* Calculate minimal possible size of index tuple by index metadata.
* Minimal possible size of varlena is VARHDRSZ.
*
* XXX: that's not actually true, as a short varlen can be just 2 bytes.
* And we should take padding into account here.
*/
itupMinSize = (Size) MAXALIGN(sizeof(IndexTupleData));
for (i = 0; i < index->rd_att->natts; i++)
{
if (index->rd_att->attrs[i]->attlen < 0)
itupMinSize += VARHDRSZ;
else
itupMinSize += index->rd_att->attrs[i]->attlen;
}
/* Calculate average and maximal number of index tuples which fit to page */
avgIndexTuplesPerPage = pageFreeSpace / itupAvgSize;
maxIndexTuplesPerPage = pageFreeSpace / itupMinSize;
/*
* We need to calculate two parameters for the buffering algorithm:
* levelStep and pagesPerBuffer.
*
* levelStep determines the size of subtree that we operate on, while
* emptying a buffer. A higher value is better, as you need fewer buffer
* emptying steps to build the index. However, if you set it too high, the
* subtree doesn't fit in cache anymore, and you quickly lose the benefit
* of the buffers.
*
* In Arge et al's paper, levelStep is chosen as logB(M/4B), where B is
* the number of tuples on page (ie. fanout), and M is the amount of
* internal memory available. Curiously, they doesn't explain *why* that
* setting is optimal. We calculate it by taking the highest levelStep so
* that a subtree still fits in cache. For a small B, our way of
* calculating levelStep is very close to Arge et al's formula. For a
* large B, our formula gives a value that is 2x higher.
*
* The average size (in pages) of a subtree of depth n can be calculated
* as a geometric series:
*
* B^0 + B^1 + B^2 + ... + B^n = (1 - B^(n + 1)) / (1 - B)
*
* where B is the average number of index tuples on page. The subtree is
* cached in the shared buffer cache and the OS cache, so we choose
* levelStep so that the subtree size is comfortably smaller than
* effective_cache_size, with a safety factor of 4.
*
* The estimate on the average number of index tuples on page is based on
* average tuple sizes observed before switching to buffered build, so the
* real subtree size can be somewhat larger. Also, it would selfish to
* gobble the whole cache for our index build. The safety factor of 4
* should account for those effects.
*
* The other limiting factor for setting levelStep is that while
* processing a subtree, we need to hold one page for each buffer at the
* next lower buffered level. The max. number of buffers needed for that
* is maxIndexTuplesPerPage^levelStep. This is very conservative, but
* hopefully maintenance_work_mem is set high enough that you're
* constrained by effective_cache_size rather than maintenance_work_mem.
*
* XXX: the buffer hash table consumes a fair amount of memory too per
* buffer, but that is not currently taken into account. That scales on
* the total number of buffers used, ie. the index size and on levelStep.
* Note that a higher levelStep *reduces* the amount of memory needed for
* the hash table.
*/
levelStep = 1;
for (;;)
{
double subtreesize;
double maxlowestlevelpages;
/* size of an average subtree at this levelStep (in pages). */
subtreesize =
(1 - pow(avgIndexTuplesPerPage, (double) (levelStep + 1))) /
(1 - avgIndexTuplesPerPage);
/* max number of pages at the lowest level of a subtree */
maxlowestlevelpages = pow(maxIndexTuplesPerPage, (double) levelStep);
/* subtree must fit in cache (with safety factor of 4) */
if (subtreesize > effective_cache_size / 4)
break;
/* each node in the lowest level of a subtree has one page in memory */
if (maxlowestlevelpages > ((double) maintenance_work_mem * 1024) / BLCKSZ)
break;
/* Good, we can handle this levelStep. See if we can go one higher. */
levelStep++;
}
/*
* We just reached an unacceptable value of levelStep in previous loop.
* So, decrease levelStep to get last acceptable value.
*/
levelStep--;
/*
* If there's not enough cache or maintenance_work_mem, fall back to plain
* inserts.
*/
if (levelStep <= 0)
{
elog(DEBUG1, "failed to switch to buffered GiST build");
buildstate->bufferingMode = GIST_BUFFERING_DISABLED;
return;
}
/*
* The second parameter to set is pagesPerBuffer, which determines the
* size of each buffer. We adjust pagesPerBuffer also during the build,
* which is why this calculation is in a separate function.
*/
pagesPerBuffer = calculatePagesPerBuffer(buildstate, levelStep);
/* Initialize GISTBuildBuffers with these parameters */
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",
levelStep, pagesPerBuffer);
}
/*
* Calculate pagesPerBuffer parameter for the buffering algorithm.
*
* Buffer size is chosen so that assuming that tuples are distributed
* randomly, emptying half a buffer fills on average one page in every buffer
* at the next lower level.
*/
static int
calculatePagesPerBuffer(GISTBuildState *buildstate, int levelStep)
{
double pagesPerBuffer;
double avgIndexTuplesPerPage;
double itupAvgSize;
Size pageFreeSpace;
/* Calc space of index page which is available for index tuples */
pageFreeSpace = BLCKSZ - SizeOfPageHeaderData - sizeof(GISTPageOpaqueData)
- sizeof(ItemIdData)
- buildstate->freespace;
/*
* Calculate average size of already inserted index tuples using gathered
* statistics.
*/
itupAvgSize = (double) buildstate->indtuplesSize /
(double) buildstate->indtuples;
avgIndexTuplesPerPage = pageFreeSpace / itupAvgSize;
/*
* Recalculate required size of buffers.
*/
pagesPerBuffer = 2 * pow(avgIndexTuplesPerPage, levelStep);
return (int) rint(pagesPerBuffer);
}
/*
* Per-tuple callback from IndexBuildHeapScan.
*/
static void
gistBuildCallback(Relation index,
HeapTuple htup,
Datum *values,
bool *isnull,
bool tupleIsAlive,
void *state)
{
GISTBuildState *buildstate = (GISTBuildState *) state;
IndexTuple itup;
MemoryContext oldCtx;
oldCtx = MemoryContextSwitchTo(buildstate->giststate->tempCxt);
/* form an index tuple and point it at the heap tuple */
itup = gistFormTuple(buildstate->giststate, index, values, isnull, true);
itup->t_tid = htup->t_self;
if (buildstate->bufferingMode == GIST_BUFFERING_ACTIVE)
{
/* We have buffers, so use them. */
gistBufferingBuildInsert(buildstate, itup);
}
else
{
/*
* There's no buffers (yet). Since we already have the index relation
* locked, we call gistdoinsert directly.
*/
gistdoinsert(index, itup, buildstate->freespace,
buildstate->giststate, buildstate->heaprel);
}
/* Update tuple count and total size. */
buildstate->indtuples += 1;
buildstate->indtuplesSize += IndexTupleSize(itup);
MemoryContextSwitchTo(oldCtx);
MemoryContextReset(buildstate->giststate->tempCxt);
if (buildstate->bufferingMode == GIST_BUFFERING_ACTIVE &&
buildstate->indtuples % BUFFERING_MODE_TUPLE_SIZE_STATS_TARGET == 0)
{
/* Adjust the target buffer size now */
buildstate->gfbb->pagesPerBuffer =
calculatePagesPerBuffer(buildstate, buildstate->gfbb->levelStep);
}
/*
* In 'auto' mode, check if the index has grown too large to fit in cache,
* and switch to buffering mode if it has.
*
* To avoid excessive calls to smgrnblocks(), only check this every
* BUFFERING_MODE_SWITCH_CHECK_STEP index tuples
*/
if ((buildstate->bufferingMode == GIST_BUFFERING_AUTO &&
buildstate->indtuples % BUFFERING_MODE_SWITCH_CHECK_STEP == 0 &&
effective_cache_size < smgrnblocks(index->rd_smgr, MAIN_FORKNUM)) ||
(buildstate->bufferingMode == GIST_BUFFERING_STATS &&
buildstate->indtuples >= BUFFERING_MODE_TUPLE_SIZE_STATS_TARGET))
{
/*
* Index doesn't fit in effective cache anymore. Try to switch to
* buffering build mode.
*/
gistInitBuffering(buildstate);
}
}
/*
* Insert function for buffering index build.
*/
static void
gistBufferingBuildInsert(GISTBuildState *buildstate, IndexTuple itup)
{
/* Insert the tuple to buffers. */
gistProcessItup(buildstate, itup, 0, buildstate->gfbb->rootlevel);
/* If we filled up (half of a) buffer, process buffer emptying. */
gistProcessEmptyingQueue(buildstate);
}
/*
* Process an index tuple. Runs the tuple down the tree until we reach a leaf
* page or node buffer, and inserts the tuple there. Returns true if we have
* to stop buffer emptying process (because one of child buffers can't take
* index tuples anymore).
*/
static bool
gistProcessItup(GISTBuildState *buildstate, IndexTuple itup,
BlockNumber startblkno, int startlevel)
{
GISTSTATE *giststate = buildstate->giststate;
GISTBuildBuffers *gfbb = buildstate->gfbb;
Relation indexrel = buildstate->indexrel;
BlockNumber childblkno;
Buffer buffer;
bool result = false;
BlockNumber blkno;
int level;
OffsetNumber downlinkoffnum = InvalidOffsetNumber;
BlockNumber parentblkno = InvalidBlockNumber;
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;
IndexTuple idxtuple,
newtup;
Page page;
OffsetNumber childoffnum;
/* Have we reached a level with buffers? */
if (LEVEL_HAS_BUFFERS(level, gfbb) && level != startlevel)
break;
/* Have we reached a leaf page? */
if (level == 0)
break;
/*
* Nope. Descend down to the next level then. Choose a child to
* descend down to.
*/
buffer = ReadBuffer(indexrel, blkno);
LockBuffer(buffer, GIST_EXCLUSIVE);
page = (Page) BufferGetPage(buffer);
childoffnum = gistchoose(indexrel, page, itup, giststate);
iid = PageGetItemId(page, childoffnum);
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)
{
blkno = gistbufferinginserttuples(buildstate,
buffer,
level,
&newtup,
1,
childoffnum,
InvalidBlockNumber,
InvalidOffsetNumber);
/* gistbufferinginserttuples() released the buffer */
}
else
UnlockReleaseBuffer(buffer);
/* Descend to the child */
parentblkno = blkno;
blkno = childblkno;
downlinkoffnum = childoffnum;
Assert(level > 0);
level--;
}
if (LEVEL_HAS_BUFFERS(level, gfbb))
{
/*
* We've reached level with buffers. Place the index tuple to the
* buffer, and add the buffer to the emptying queue if it overflows.
*/
GISTNodeBuffer *childNodeBuffer;
/* Find the buffer or create a new one */
childNodeBuffer = gistGetNodeBuffer(gfbb, giststate, blkno, level);
/* Add index tuple to it */
gistPushItupToNodeBuffer(gfbb, childNodeBuffer, itup);
if (BUFFER_OVERFLOWED(childNodeBuffer, gfbb))
result = true;
}
else
{
/*
* We've reached a leaf page. Place the tuple here.
*/
Assert(level == 0);
buffer = ReadBuffer(indexrel, blkno);
LockBuffer(buffer, GIST_EXCLUSIVE);
gistbufferinginserttuples(buildstate, buffer, level,
&itup, 1, InvalidOffsetNumber,
parentblkno, downlinkoffnum);
/* gistbufferinginserttuples() released the buffer */
}
return result;
}
/*
* Insert tuples to a given page.
*
* This is analogous with gistinserttuples() in the regular insertion code.
*
* Returns the block number of the page where the (first) new or updated tuple
* was inserted. Usually that's the original page, but might be a sibling page
* if the original page was split.
*
* Caller should hold a lock on 'buffer' on entry. This function will unlock
* and unpin it.
*/
static BlockNumber
gistbufferinginserttuples(GISTBuildState *buildstate, Buffer buffer, int level,
IndexTuple *itup, int ntup, OffsetNumber oldoffnum,
BlockNumber parentblk, OffsetNumber downlinkoffnum)
{
GISTBuildBuffers *gfbb = buildstate->gfbb;
List *splitinfo;
bool is_split;
BlockNumber placed_to_blk = InvalidBlockNumber;
is_split = gistplacetopage(buildstate->indexrel,
buildstate->freespace,
buildstate->giststate,
buffer,
itup, ntup, oldoffnum, &placed_to_blk,
InvalidBuffer,
&splitinfo,
false,
buildstate->heaprel);
/*
* If this is a root split, update the root path item kept in memory. This
* ensures that all path stacks are always complete, including all parent
* nodes up to the root. That simplifies the algorithm to re-find correct
* parent.
*/
if (is_split && BufferGetBlockNumber(buffer) == GIST_ROOT_BLKNO)
{
Page page = BufferGetPage(buffer);
OffsetNumber off;
OffsetNumber maxoff;
Assert(level == gfbb->rootlevel);
gfbb->rootlevel++;
elog(DEBUG2, "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. Visit all the new child pages to memorize the parents of the
* grandchildren.
*/
if (gfbb->rootlevel > 1)
{
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));
Buffer childbuf = ReadBuffer(buildstate->indexrel, childblkno);
LockBuffer(childbuf, GIST_SHARE);
gistMemorizeAllDownlinks(buildstate, childbuf);
UnlockReleaseBuffer(childbuf);
/*
* Also remember that the parent of the new child page is the
* root block.
*/
gistMemorizeParent(buildstate, childblkno, GIST_ROOT_BLKNO);
}
}
}
if (splitinfo)
{
/*
* 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 on internal nodes and
* the parent map.
*/
IndexTuple *downlinks;
int ndownlinks,
i;
Buffer parentBuffer;
ListCell *lc;
/* Parent may have changed since we memorized this path. */
parentBuffer =
gistBufferingFindCorrectParent(buildstate,
BufferGetBlockNumber(buffer),
level,
&parentblk,
&downlinkoffnum);
/*
* If there's a buffer associated with this page, that needs to be
* split too. gistRelocateBuildBuffersOnSplit() will also adjust the
* downlinks in 'splitinfo', to make sure they're consistent not only
* with the tuples already on the pages, but also the tuples in the
* buffers that will eventually be inserted to them.
*/
gistRelocateBuildBuffersOnSplit(gfbb,
buildstate->giststate,
buildstate->indexrel,
level,
buffer, splitinfo);
/* Create an array of all the downlink tuples */
ndownlinks = list_length(splitinfo);
downlinks = (IndexTuple *) palloc(sizeof(IndexTuple) * ndownlinks);
i = 0;
foreach(lc, splitinfo)
{
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. This includes the original page.
*/
UnlockReleaseBuffer(splitinfo->buf);
downlinks[i++] = splitinfo->downlink;
}
/* Insert them into parent. */
gistbufferinginserttuples(buildstate, parentBuffer, level + 1,
downlinks, ndownlinks, downlinkoffnum,
InvalidBlockNumber, InvalidOffsetNumber);
list_free_deep(splitinfo); /* we don't need this anymore */
}
else
UnlockReleaseBuffer(buffer);
return placed_to_blk;
}
/*
* Find the downlink pointing to a child page.
*
* 'childblkno' indicates the child page to find the parent for. 'level' is
* the level of the child. On entry, *parentblkno and *downlinkoffnum can
* point to a location where the downlink used to be - we will check that
* location first, and save some cycles if it hasn't moved. The function
* returns a buffer containing the downlink, exclusively-locked, and
* *parentblkno and *downlinkoffnum are set to the real location of the
* downlink.
*
* If the child page is a leaf (level == 0), the caller must supply a correct
* parentblkno. Otherwise we use the parent map hash table to find the parent
* block.
*
* This function serves the same purpose as gistFindCorrectParent() during
* normal index inserts, but this is simpler because we don't need to deal
* with concurrent inserts.
*/
static Buffer
gistBufferingFindCorrectParent(GISTBuildState *buildstate,
BlockNumber childblkno, int level,
BlockNumber *parentblkno,
OffsetNumber *downlinkoffnum)
{
BlockNumber parent;
Buffer buffer;
Page page;
OffsetNumber maxoff;
OffsetNumber off;
if (level > 0)
parent = gistGetParent(buildstate, childblkno);
else
{
/*
* For a leaf page, the caller must supply a correct parent block
* number.
*/
if (*parentblkno == InvalidBlockNumber)
elog(ERROR, "no parent buffer provided of child %d", childblkno);
parent = *parentblkno;
}
buffer = ReadBuffer(buildstate->indexrel, parent);
page = BufferGetPage(buffer);
LockBuffer(buffer, GIST_EXCLUSIVE);
gistcheckpage(buildstate->indexrel, buffer);
maxoff = PageGetMaxOffsetNumber(page);
/* Check if it was not moved */
if (parent == *parentblkno && *parentblkno != InvalidBlockNumber &&
*downlinkoffnum != InvalidOffsetNumber && *downlinkoffnum <= maxoff)
{
ItemId iid = PageGetItemId(page, *downlinkoffnum);
IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
if (ItemPointerGetBlockNumber(&(idxtuple->t_tid)) == childblkno)
{
/* Still there */
return buffer;
}
}
/*
* 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))
{
ItemId iid = PageGetItemId(page, off);
IndexTuple idxtuple = (IndexTuple) PageGetItem(page, iid);
if (ItemPointerGetBlockNumber(&(idxtuple->t_tid)) == childblkno)
{
/* yes!!, found it */
*downlinkoffnum = off;
return buffer;
}
}
elog(ERROR, "failed to re-find parent for block %u", childblkno);
return InvalidBuffer; /* keep compiler quiet */
}
/*
* Process buffers emptying stack. Emptying of one buffer can cause emptying
* of other buffers. This function iterates until this cascading emptying
* process finished, e.g. until buffers emptying stack is empty.
*/
static void
gistProcessEmptyingQueue(GISTBuildState *buildstate)
{
GISTBuildBuffers *gfbb = buildstate->gfbb;
/* Iterate while we have elements in buffers emptying stack. */
while (gfbb->bufferEmptyingQueue != NIL)
{
GISTNodeBuffer *emptyingNodeBuffer;
/* Get node buffer from emptying stack. */
emptyingNodeBuffer = (GISTNodeBuffer *) linitial(gfbb->bufferEmptyingQueue);
gfbb->bufferEmptyingQueue = list_delete_first(gfbb->bufferEmptyingQueue);
emptyingNodeBuffer->queuedForEmptying = false;
/*
* We are going to load last pages of buffers where emptying will be
* to. So let's unload any previously loaded buffers.
*/
gistUnloadNodeBuffers(gfbb);
/*
* Pop tuples from the buffer and run them down to the buffers at
* lower level, or leaf pages. We continue until one of the lower
* level buffers fills up, or this buffer runs empty.
*
* In Arge et al's paper, the buffer emptying is stopped after
* processing 1/2 node buffer worth of tuples, to avoid overfilling
* any of the lower level buffers. However, it's more efficient to
* keep going until one of the lower level buffers actually fills up,
* so that's what we do. This doesn't need to be exact, if a buffer
* overfills by a few tuples, there's no harm done.
*/
while (true)
{
IndexTuple itup;
/* Get next index tuple from the buffer */
if (!gistPopItupFromNodeBuffer(gfbb, emptyingNodeBuffer, &itup))
break;
/*
* Run it down to the underlying node buffer or leaf page.
*
* Note: it's possible that the buffer we're emptying splits as a
* result of this call. If that happens, our emptyingNodeBuffer
* points to the left half of the split. After split, it's very
* likely that the new left buffer is no longer over the half-full
* threshold, but we might as well keep flushing tuples from it
* until we fill a lower-level buffer.
*/
if (gistProcessItup(buildstate, itup, emptyingNodeBuffer->nodeBlocknum, emptyingNodeBuffer->level))
{
/*
* A lower level buffer filled up. Stop emptying this buffer,
* to avoid overflowing the lower level buffer.
*/
break;
}
/* Free all the memory allocated during index tuple processing */
MemoryContextReset(buildstate->giststate->tempCxt);
}
}
}
/*
* Empty all node buffers, from top to bottom. This is done at the end of
* index build to flush all remaining tuples to the index.
*
* Note: This destroys the buffersOnLevels lists, so the buffers should not
* be inserted to after this call.
*/
static void
gistEmptyAllBuffers(GISTBuildState *buildstate)
{
GISTBuildBuffers *gfbb = buildstate->gfbb;
MemoryContext oldCtx;
int i;
oldCtx = MemoryContextSwitchTo(buildstate->giststate->tempCxt);
/*
* Iterate through the levels from top to bottom.
*/
for (i = gfbb->buffersOnLevelsLen - 1; i >= 0; i--)
{
/*
* Empty all buffers on this level. Note that new buffers can pop up
* in the list during the processing, as a result of page splits, so a
* simple walk through the list won't work. We remove buffers from the
* list when we see them empty; a buffer can't become non-empty once
* it's been fully emptied.
*/
while (gfbb->buffersOnLevels[i] != NIL)
{
GISTNodeBuffer *nodeBuffer;
nodeBuffer = (GISTNodeBuffer *) linitial(gfbb->buffersOnLevels[i]);
if (nodeBuffer->blocksCount != 0)
{
/*
* Add this buffer to the emptying queue, and proceed to empty
* the queue.
*/
if (!nodeBuffer->queuedForEmptying)
{
MemoryContextSwitchTo(gfbb->context);
nodeBuffer->queuedForEmptying = true;
gfbb->bufferEmptyingQueue =
lcons(nodeBuffer, gfbb->bufferEmptyingQueue);
MemoryContextSwitchTo(buildstate->giststate->tempCxt);
}
gistProcessEmptyingQueue(buildstate);
}
else
gfbb->buffersOnLevels[i] =
list_delete_first(gfbb->buffersOnLevels[i]);
}
elog(DEBUG2, "emptied all buffers at level %d", i);
}
MemoryContextSwitchTo(oldCtx);
}
/*
* Get the depth of the GiST index.
*/
static int
gistGetMaxLevel(Relation index)
{
int maxLevel;
BlockNumber blkno;
/*
* Traverse down the tree, starting from the root, until we hit the leaf
* level.
*/
maxLevel = 0;
blkno = GIST_ROOT_BLKNO;
while (true)
{
Buffer buffer;
Page page;
IndexTuple itup;
buffer = ReadBuffer(index, blkno);
/*
* There's no concurrent access during index build, so locking is just
* pro forma.
*/
LockBuffer(buffer, GIST_SHARE);
page = (Page) BufferGetPage(buffer);
if (GistPageIsLeaf(page))
{
/* We hit the bottom, so we're done. */
UnlockReleaseBuffer(buffer);
break;
}
/*
* Pick the first downlink on the page, and follow it. It doesn't
* matter which downlink we choose, the tree has the same depth
* everywhere, so we just pick the first one.
*/
itup = (IndexTuple) PageGetItem(page,
PageGetItemId(page, FirstOffsetNumber));
blkno = ItemPointerGetBlockNumber(&(itup->t_tid));
UnlockReleaseBuffer(buffer);
/*
* We're going down on the tree. It means that there is yet one more
* 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;
} ParentMapEntry;
static void
gistInitParentMap(GISTBuildState *buildstate)
{
HASHCTL hashCtl;
hashCtl.keysize = sizeof(BlockNumber);
hashCtl.entrysize = sizeof(ParentMapEntry);
hashCtl.hcxt = CurrentMemoryContext;
buildstate->parentMap = hash_create("gistbuild parent map",
1024,
&hashCtl,
HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
}
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;
}
/*
* Scan all downlinks on a page, and memorize their 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;
}