* Copyright (c) 2003-2005, PostgreSQL Global Development Group
*
* IDENTIFICATION
- * $PostgreSQL: pgsql/src/backend/nodes/tidbitmap.c,v 1.2 2005/04/19 22:35:15 tgl Exp $
+ * $PostgreSQL: pgsql/src/backend/nodes/tidbitmap.c,v 1.3 2005/05/17 00:43:47 tgl Exp $
*
*-------------------------------------------------------------------------
*/
} PagetableEntry;
/*
+ * dynahash.c is optimized for relatively large, long-lived hash tables.
+ * This is not ideal for TIDBitMap, particularly when we are using a bitmap
+ * scan on the inside of a nestloop join: a bitmap may well live only long
+ * enough to accumulate one entry in such cases. We therefore avoid creating
+ * an actual hashtable until we need two pagetable entries. When just one
+ * pagetable entry is needed, we store it in a fixed field of TIDBitMap.
+ * (NOTE: we don't get rid of the hashtable if the bitmap later shrinks down
+ * to zero or one page again. So, status can be TBM_HASH even when nentries
+ * is zero or one.)
+ */
+typedef enum
+{
+ TBM_EMPTY, /* no hashtable, nentries == 0 */
+ TBM_ONE_PAGE, /* entry1 contains the single entry */
+ TBM_HASH /* pagetable is valid, entry1 is not */
+} TBMStatus;
+
+/*
* Here is the representation for a whole TIDBitMap:
*/
struct TIDBitmap
{
NodeTag type; /* to make it a valid Node */
MemoryContext mcxt; /* memory context containing me */
+ TBMStatus status; /* see codes above */
HTAB *pagetable; /* hash table of PagetableEntry's */
int nentries; /* number of entries in pagetable */
int maxentries; /* limit on same to meet maxbytes */
int npages; /* number of exact entries in pagetable */
int nchunks; /* number of lossy entries in pagetable */
bool iterating; /* tbm_begin_iterate called? */
+ PagetableEntry entry1; /* used when status == TBM_ONE_PAGE */
/* the remaining fields are used while producing sorted output: */
- TBMIterateResult *output; /* NULL if not yet created */
PagetableEntry **spages; /* sorted exact-page list, or NULL */
PagetableEntry **schunks; /* sorted lossy-chunk list, or NULL */
int spageptr; /* next spages index */
int schunkptr; /* next schunks index */
int schunkbit; /* next bit to check in current schunk */
+ TBMIterateResult output; /* MUST BE LAST (because variable-size) */
};
/* Local function prototypes */
-static PagetableEntry *tbm_find_pageentry(const TIDBitmap *tbm,
- BlockNumber pageno);
+static void tbm_union_page(TIDBitmap *a, const PagetableEntry *bpage);
+static bool tbm_intersect_page(PagetableEntry *apage, const TIDBitmap *b);
+static const PagetableEntry *tbm_find_pageentry(const TIDBitmap *tbm,
+ BlockNumber pageno);
static PagetableEntry *tbm_get_pageentry(TIDBitmap *tbm, BlockNumber pageno);
static bool tbm_page_is_lossy(const TIDBitmap *tbm, BlockNumber pageno);
static void tbm_mark_page_lossy(TIDBitmap *tbm, BlockNumber pageno);
tbm_create(long maxbytes)
{
TIDBitmap *tbm;
- HASHCTL hash_ctl;
long nbuckets;
- tbm = makeNode(TIDBitmap);
- /* we rely on makeNode to have zeroed all the fields */
+ /*
+ * Create the TIDBitmap struct, with enough trailing space to serve
+ * the needs of the TBMIterateResult sub-struct.
+ */
+ tbm = (TIDBitmap *) palloc(sizeof(TIDBitmap) +
+ MAX_TUPLES_PER_PAGE * sizeof(OffsetNumber));
+ /* Zero all the fixed fields */
+ MemSetAligned(tbm, 0, sizeof(TIDBitmap));
+
+ tbm->type = T_TIDBitmap; /* Set NodeTag */
tbm->mcxt = CurrentMemoryContext;
+ tbm->status = TBM_EMPTY;
/*
* Estimate number of hashtable entries we can have within maxbytes.
* This estimates the hash overhead at MAXALIGN(sizeof(HASHELEMENT))
* plus a pointer per hash entry, which is crude but good enough for
- * our purpose. (NOTE: this does not count the space for data
- * structures created during iteration readout.)
+ * our purpose. Also count an extra Pointer per entry for the arrays
+ * created during iteration readout.
*/
nbuckets = maxbytes /
(MAXALIGN(sizeof(HASHELEMENT)) + MAXALIGN(sizeof(PagetableEntry))
- + sizeof(Pointer));
+ + sizeof(Pointer) + sizeof(Pointer));
nbuckets = Min(nbuckets, INT_MAX-1); /* safety limit */
+ nbuckets = Max(nbuckets, 16); /* sanity limit */
tbm->maxentries = (int) nbuckets;
+ return tbm;
+}
+
+/*
+ * Actually create the hashtable. Since this is a moderately expensive
+ * proposition, we don't do it until we have to.
+ */
+static void
+tbm_create_pagetable(TIDBitmap *tbm)
+{
+ HASHCTL hash_ctl;
+
+ Assert(tbm->status != TBM_HASH);
+ Assert(tbm->pagetable == NULL);
+
+ /* Create the hashtable proper */
MemSet(&hash_ctl, 0, sizeof(hash_ctl));
hash_ctl.keysize = sizeof(BlockNumber);
hash_ctl.entrysize = sizeof(PagetableEntry);
hash_ctl.hash = tag_hash;
- hash_ctl.hcxt = CurrentMemoryContext;
+ hash_ctl.hcxt = tbm->mcxt;
tbm->pagetable = hash_create("TIDBitmap",
128, /* start small and extend */
&hash_ctl,
HASH_ELEM | HASH_FUNCTION | HASH_CONTEXT);
- return tbm;
+ /* If entry1 is valid, push it into the hashtable */
+ if (tbm->status == TBM_ONE_PAGE)
+ {
+ PagetableEntry *page;
+ bool found;
+
+ page = (PagetableEntry *) hash_search(tbm->pagetable,
+ (void *) &tbm->entry1.blockno,
+ HASH_ENTER, &found);
+ if (page == NULL)
+ ereport(ERROR,
+ (errcode(ERRCODE_OUT_OF_MEMORY),
+ errmsg("out of memory")));
+ Assert(!found);
+ memcpy(page, &tbm->entry1, sizeof(PagetableEntry));
+ }
+
+ tbm->status = TBM_HASH;
}
/*
void
tbm_free(TIDBitmap *tbm)
{
- hash_destroy(tbm->pagetable);
- if (tbm->output)
- pfree(tbm->output);
+ if (tbm->pagetable)
+ hash_destroy(tbm->pagetable);
if (tbm->spages)
pfree(tbm->spages);
if (tbm->schunks)
void
tbm_union(TIDBitmap *a, const TIDBitmap *b)
{
- HASH_SEQ_STATUS status;
+ Assert(!a->iterating);
+ /* Nothing to do if b is empty */
+ if (b->nentries == 0)
+ return;
+ /* Scan through chunks and pages in b, merge into a */
+ if (b->status == TBM_ONE_PAGE)
+ tbm_union_page(a, &b->entry1);
+ else
+ {
+ HASH_SEQ_STATUS status;
+ PagetableEntry *bpage;
+
+ Assert(b->status == TBM_HASH);
+ hash_seq_init(&status, b->pagetable);
+ while ((bpage = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ tbm_union_page(a, bpage);
+ }
+}
+
+/* Process one page of b during a union op */
+static void
+tbm_union_page(TIDBitmap *a, const PagetableEntry *bpage)
+{
PagetableEntry *apage;
- PagetableEntry *bpage;
int wordnum;
- Assert(!a->iterating);
- /* Scan through chunks and pages in b, merge into a */
- hash_seq_init(&status, b->pagetable);
- while ((bpage = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ if (bpage->ischunk)
{
- if (bpage->ischunk)
+ /* Scan b's chunk, mark each indicated page lossy in a */
+ for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
{
- /* Scan b's chunk, mark each indicated page lossy in a */
- for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
+ bitmapword w = bpage->words[wordnum];
+
+ if (w != 0)
{
- bitmapword w = bpage->words[wordnum];
+ BlockNumber pg;
- if (w != 0)
+ pg = bpage->blockno + (wordnum * BITS_PER_BITMAPWORD);
+ while (w != 0)
{
- BlockNumber pg;
-
- pg = bpage->blockno + (wordnum * BITS_PER_BITMAPWORD);
- while (w != 0)
- {
- if (w & 1)
- tbm_mark_page_lossy(a, pg);
- pg++;
- w >>= 1;
- }
+ if (w & 1)
+ tbm_mark_page_lossy(a, pg);
+ pg++;
+ w >>= 1;
}
}
}
- else if (tbm_page_is_lossy(a, bpage->blockno))
+ }
+ else if (tbm_page_is_lossy(a, bpage->blockno))
+ {
+ /* page is already lossy in a, nothing to do */
+ return;
+ }
+ else
+ {
+ apage = tbm_get_pageentry(a, bpage->blockno);
+ if (apage->ischunk)
{
- /* page is already lossy in a, nothing to do */
- continue;
+ /* The page is a lossy chunk header, set bit for itself */
+ apage->words[0] |= ((bitmapword) 1 << 0);
}
else
{
- apage = tbm_get_pageentry(a, bpage->blockno);
- if (apage->ischunk)
- {
- /* The page is a lossy chunk header, set bit for itself */
- apage->words[0] |= ((bitmapword) 1 << 0);
- }
- else
- {
- /* Both pages are exact, merge at the bit level */
- for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
- apage->words[wordnum] |= bpage->words[wordnum];
- }
+ /* Both pages are exact, merge at the bit level */
+ for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
+ apage->words[wordnum] |= bpage->words[wordnum];
}
-
- if (a->nentries > a->maxentries)
- tbm_lossify(a);
}
+
+ if (a->nentries > a->maxentries)
+ tbm_lossify(a);
}
/*
void
tbm_intersect(TIDBitmap *a, const TIDBitmap *b)
{
- HASH_SEQ_STATUS status;
- PagetableEntry *apage;
- PagetableEntry *bpage;
- int wordnum;
-
Assert(!a->iterating);
+ /* Nothing to do if a is empty */
+ if (a->nentries == 0)
+ return;
/* Scan through chunks and pages in a, try to match to b */
- hash_seq_init(&status, a->pagetable);
- while ((apage = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ if (a->status == TBM_ONE_PAGE)
{
- if (apage->ischunk)
+ if (tbm_intersect_page(&a->entry1, b))
{
- /* Scan each bit in chunk, try to clear */
- bool candelete = true;
-
- for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
- {
- bitmapword w = apage->words[wordnum];
-
- if (w != 0)
- {
- bitmapword neww = w;
- BlockNumber pg;
- int bitnum;
+ /* Page is now empty, remove it from a */
+ Assert(!a->entry1.ischunk);
+ a->npages--;
+ a->nentries--;
+ Assert(a->nentries == 0);
+ a->status = TBM_EMPTY;
+ }
+ }
+ else
+ {
+ HASH_SEQ_STATUS status;
+ PagetableEntry *apage;
- pg = apage->blockno + (wordnum * BITS_PER_BITMAPWORD);
- bitnum = 0;
- while (w != 0)
- {
- if (w & 1)
- {
- if (!tbm_page_is_lossy(b, pg) &&
- tbm_find_pageentry(b, pg) == NULL)
- {
- /* Page is not in b at all, lose lossy bit */
- neww &= ~((bitmapword) 1 << bitnum);
- }
- }
- pg++;
- bitnum++;
- w >>= 1;
- }
- apage->words[wordnum] = neww;
- if (neww != 0)
- candelete = false;
- }
- }
- if (candelete)
+ Assert(a->status == TBM_HASH);
+ hash_seq_init(&status, a->pagetable);
+ while ((apage = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ {
+ if (tbm_intersect_page(apage, b))
{
- /* Chunk is now empty, remove it from a */
+ /* Page or chunk is now empty, remove it from a */
+ if (apage->ischunk)
+ a->nchunks--;
+ else
+ a->npages--;
+ a->nentries--;
if (hash_search(a->pagetable,
(void *) &apage->blockno,
HASH_REMOVE, NULL) == NULL)
elog(ERROR, "hash table corrupted");
- a->nentries--;
- a->nchunks--;
}
}
- else if (tbm_page_is_lossy(b, apage->blockno))
- {
- /* page is lossy in b, cannot clear any bits */
- continue;
- }
- else
+ }
+}
+
+/*
+ * Process one page of a during an intersection op
+ *
+ * Returns TRUE if apage is now empty and should be deleted from a
+ */
+static bool
+tbm_intersect_page(PagetableEntry *apage, const TIDBitmap *b)
+{
+ const PagetableEntry *bpage;
+ int wordnum;
+
+ if (apage->ischunk)
+ {
+ /* Scan each bit in chunk, try to clear */
+ bool candelete = true;
+
+ for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
{
- bool candelete = true;
+ bitmapword w = apage->words[wordnum];
- bpage = tbm_find_pageentry(b, apage->blockno);
- if (bpage != NULL)
+ if (w != 0)
{
- /* Both pages are exact, merge at the bit level */
- Assert(!bpage->ischunk);
- for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
+ bitmapword neww = w;
+ BlockNumber pg;
+ int bitnum;
+
+ pg = apage->blockno + (wordnum * BITS_PER_BITMAPWORD);
+ bitnum = 0;
+ while (w != 0)
{
- apage->words[wordnum] &= bpage->words[wordnum];
- if (apage->words[wordnum] != 0)
- candelete = false;
+ if (w & 1)
+ {
+ if (!tbm_page_is_lossy(b, pg) &&
+ tbm_find_pageentry(b, pg) == NULL)
+ {
+ /* Page is not in b at all, lose lossy bit */
+ neww &= ~((bitmapword) 1 << bitnum);
+ }
+ }
+ pg++;
+ bitnum++;
+ w >>= 1;
}
+ apage->words[wordnum] = neww;
+ if (neww != 0)
+ candelete = false;
}
- if (candelete)
+ }
+ return candelete;
+ }
+ else if (tbm_page_is_lossy(b, apage->blockno))
+ {
+ /* page is lossy in b, cannot clear any bits */
+ return false;
+ }
+ else
+ {
+ bool candelete = true;
+
+ bpage = tbm_find_pageentry(b, apage->blockno);
+ if (bpage != NULL)
+ {
+ /* Both pages are exact, merge at the bit level */
+ Assert(!bpage->ischunk);
+ for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
{
- /* Page is now empty, remove it from a */
- if (hash_search(a->pagetable,
- (void *) &apage->blockno,
- HASH_REMOVE, NULL) == NULL)
- elog(ERROR, "hash table corrupted");
- a->nentries--;
- a->npages--;
+ apage->words[wordnum] &= bpage->words[wordnum];
+ if (apage->words[wordnum] != 0)
+ candelete = false;
}
}
+ return candelete;
}
}
tbm->iterating = true;
/*
- * Allocate the output data structure if we didn't already.
- * (We don't do this during tbm_create since it's entirely possible
- * that a TIDBitmap will live and die without ever being iterated.)
+ * Reset iteration pointers.
+ */
+ tbm->spageptr = 0;
+ tbm->schunkptr = 0;
+ tbm->schunkbit = 0;
+ /*
+ * Nothing else to do if no entries, nor if we don't have a hashtable.
*/
- if (!tbm->output)
- tbm->output = (TBMIterateResult *)
- MemoryContextAllocZero(tbm->mcxt,
- sizeof(TBMIterateResult) +
- MAX_TUPLES_PER_PAGE * sizeof(OffsetNumber));
+ if (tbm->nentries == 0 || tbm->status != TBM_HASH)
+ return;
/*
* Create and fill the sorted page lists if we didn't already.
*/
qsort(tbm->spages, npages, sizeof(PagetableEntry *), tbm_comparator);
if (nchunks > 1)
qsort(tbm->schunks, nchunks, sizeof(PagetableEntry *), tbm_comparator);
- /*
- * Reset iteration pointers.
- */
- tbm->spageptr = 0;
- tbm->schunkptr = 0;
- tbm->schunkbit = 0;
}
/*
TBMIterateResult *
tbm_iterate(TIDBitmap *tbm)
{
- TBMIterateResult *output = tbm->output;
+ TBMIterateResult *output = &(tbm->output);
Assert(tbm->iterating);
/*
if (tbm->spageptr < tbm->npages)
{
- PagetableEntry *page = tbm->spages[tbm->spageptr];
+ PagetableEntry *page;
int ntuples;
int wordnum;
+ /* In ONE_PAGE state, we don't allocate an spages[] array */
+ if (tbm->status == TBM_ONE_PAGE)
+ page = &tbm->entry1;
+ else
+ page = tbm->spages[tbm->spageptr];
+
/* scan bitmap to extract individual offset numbers */
ntuples = 0;
for (wordnum = 0; wordnum < WORDS_PER_PAGE; wordnum++)
*
* Returns NULL if there is no non-lossy entry for the pageno.
*/
-static PagetableEntry *
+static const PagetableEntry *
tbm_find_pageentry(const TIDBitmap *tbm, BlockNumber pageno)
{
- PagetableEntry *page;
+ const PagetableEntry *page;
+
+ if (tbm->nentries == 0) /* in case pagetable doesn't exist */
+ return NULL;
+
+ if (tbm->status == TBM_ONE_PAGE)
+ {
+ page = &tbm->entry1;
+ if (page->blockno != pageno)
+ return NULL;
+ Assert(!page->ischunk);
+ return page;
+ }
page = (PagetableEntry *) hash_search(tbm->pagetable,
(void *) &pageno,
PagetableEntry *page;
bool found;
- /* Look up or create an entry */
- page = (PagetableEntry *) hash_search(tbm->pagetable,
- (void *) &pageno,
- HASH_ENTER, &found);
- if (page == NULL)
- ereport(ERROR,
- (errcode(ERRCODE_OUT_OF_MEMORY),
- errmsg("out of memory")));
+ if (tbm->status == TBM_EMPTY)
+ {
+ /* Use the fixed slot */
+ page = &tbm->entry1;
+ found = false;
+ tbm->status = TBM_ONE_PAGE;
+ }
+ else
+ {
+ if (tbm->status == TBM_ONE_PAGE)
+ {
+ page = &tbm->entry1;
+ if (page->blockno == pageno)
+ return page;
+ /* Time to switch from one page to a hashtable */
+ tbm_create_pagetable(tbm);
+ }
+
+ /* Look up or create an entry */
+ page = (PagetableEntry *) hash_search(tbm->pagetable,
+ (void *) &pageno,
+ HASH_ENTER, &found);
+ if (page == NULL)
+ ereport(ERROR,
+ (errcode(ERRCODE_OUT_OF_MEMORY),
+ errmsg("out of memory")));
+ }
/* Initialize it if not present before */
if (!found)
/* we can skip the lookup if there are no lossy chunks */
if (tbm->nchunks == 0)
return false;
+ Assert(tbm->status == TBM_HASH);
bitno = pageno % PAGES_PER_CHUNK;
chunk_pageno = pageno - bitno;
int wordnum;
int bitnum;
+ /* We force the bitmap into hashtable mode whenever it's lossy */
+ if (tbm->status != TBM_HASH)
+ tbm_create_pagetable(tbm);
+
bitno = pageno % PAGES_PER_CHUNK;
chunk_pageno = pageno - bitno;
* during each call.
*/
Assert(!tbm->iterating);
+ Assert(tbm->status == TBM_HASH);
+
hash_seq_init(&status, tbm->pagetable);
while ((page = (PagetableEntry *) hash_seq_search(&status)) != NULL)
{
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