#include "access/htup_details.h"
#include "nodes/bitmapset.h"
#include "nodes/tidbitmap.h"
-#include "utils/hsearch.h"
/*
* The maximum number of tuples per page is not large (typically 256 with
* for that page in the page table.
*
* We actually store both exact pages and lossy chunks in the same hash
- * table, using identical data structures. (This is because dynahash.c's
- * memory management doesn't allow space to be transferred easily from one
- * hashtable to another.) Therefore it's best if PAGES_PER_CHUNK is the
- * same as MAX_TUPLES_PER_PAGE, or at least not too different. But we
- * also want PAGES_PER_CHUNK to be a power of 2 to avoid expensive integer
- * remainder operations. So, define it like this:
+ * table, using identical data structures. (This is because the memory
+ * management for hashtables doesn't easily/efficiently allow space to be
+ * transferred easily from one hashtable to another.) Therefore it's best
+ * if PAGES_PER_CHUNK is the same as MAX_TUPLES_PER_PAGE, or at least not
+ * too different. But we also want PAGES_PER_CHUNK to be a power of 2 to
+ * avoid expensive integer remainder operations. So, define it like this:
*/
#define PAGES_PER_CHUNK (BLCKSZ / 32)
typedef struct PagetableEntry
{
BlockNumber blockno; /* page number (hashtable key) */
+ char status; /* hash entry status */
bool ischunk; /* T = lossy storage, F = exact */
bool recheck; /* should the tuples be rechecked? */
bitmapword words[Max(WORDS_PER_PAGE, WORDS_PER_CHUNK)];
} 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.)
+ * We want to avoid the overhead of creating the hashtable, which is
+ * comparatively large, when not necessary. 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
{
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 */
+ struct pagetable_hash *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? */
+ uint32 lossify_start; /* offset to start lossifying hashtable at */
PagetableEntry entry1; /* used when status == TBM_ONE_PAGE */
/* these are valid when iterating is true: */
PagetableEntry **spages; /* sorted exact-page list, or NULL */
static void tbm_lossify(TIDBitmap *tbm);
static int tbm_comparator(const void *left, const void *right);
+/*
+ * Simple inline murmur hash implementation for the exact width required, for
+ * performance.
+ */
+static inline uint32
+hash_blockno(BlockNumber b)
+{
+ uint32 h = b;
+
+ h ^= h >> 16;
+ h *= 0x85ebca6b;
+ h ^= h >> 13;
+ h *= 0xc2b2ae35;
+ h ^= h >> 16;
+ return h;
+}
+
+/* define hashtable mapping block numbers to PagetableEntry's */
+#define SH_PREFIX pagetable
+#define SH_ELEMENT_TYPE PagetableEntry
+#define SH_KEY_TYPE BlockNumber
+#define SH_KEY blockno
+#define SH_HASH_KEY(tb, key) hash_blockno(key)
+#define SH_EQUAL(tb, a, b) a == b
+#define SH_SCOPE static inline
+#define SH_DEFINE
+#define SH_DECLARE
+#include "lib/simplehash.h"
+
/*
* tbm_create - create an initially-empty bitmap
/*
* 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.
- * Also count an extra Pointer per entry for the arrays created during
- * iteration readout.
+ * estimates the hash cost as sizeof(PagetableEntry), which is good enough
+ * for 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(PagetableEntry) + sizeof(Pointer) + sizeof(Pointer));
nbuckets = Min(nbuckets, INT_MAX - 1); /* safety limit */
nbuckets = Max(nbuckets, 16); /* sanity limit */
tbm->maxentries = (int) nbuckets;
+ tbm->lossify_start = 0;
return tbm;
}
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.hcxt = tbm->mcxt;
- tbm->pagetable = hash_create("TIDBitmap",
- 128, /* start small and extend */
- &hash_ctl,
- HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
+ tbm->pagetable = pagetable_create(tbm->mcxt, 128);
/* If entry1 is valid, push it into the hashtable */
if (tbm->status == TBM_ONE_PAGE)
{
PagetableEntry *page;
bool found;
+ char oldstatus;
- page = (PagetableEntry *) hash_search(tbm->pagetable,
- (void *) &tbm->entry1.blockno,
- HASH_ENTER, &found);
+ page = pagetable_insert(tbm->pagetable,
+ tbm->entry1.blockno,
+ &found);
Assert(!found);
+ oldstatus = page->status;
memcpy(page, &tbm->entry1, sizeof(PagetableEntry));
+ page->status = oldstatus;
}
tbm->status = TBM_HASH;
tbm_free(TIDBitmap *tbm)
{
if (tbm->pagetable)
- hash_destroy(tbm->pagetable);
+ pagetable_destroy(tbm->pagetable);
if (tbm->spages)
pfree(tbm->spages);
if (tbm->schunks)
tbm_union_page(a, &b->entry1);
else
{
- HASH_SEQ_STATUS status;
+ pagetable_iterator i;
PagetableEntry *bpage;
Assert(b->status == TBM_HASH);
- hash_seq_init(&status, b->pagetable);
- while ((bpage = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ pagetable_start_iterate(b->pagetable, &i);
+ while ((bpage = pagetable_iterate(b->pagetable, &i)) != NULL)
tbm_union_page(a, bpage);
}
}
}
else
{
- HASH_SEQ_STATUS status;
+ pagetable_iterator i;
PagetableEntry *apage;
Assert(a->status == TBM_HASH);
- hash_seq_init(&status, a->pagetable);
- while ((apage = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ pagetable_start_iterate(a->pagetable, &i);
+ while ((apage = pagetable_iterate(a->pagetable, &i)) != NULL)
{
if (tbm_intersect_page(a, apage, b))
{
else
a->npages--;
a->nentries--;
- if (hash_search(a->pagetable,
- (void *) &apage->blockno,
- HASH_REMOVE, NULL) == NULL)
+ if (!pagetable_delete(a->pagetable, apage->blockno))
elog(ERROR, "hash table corrupted");
}
}
*/
if (tbm->status == TBM_HASH && !tbm->iterating)
{
- HASH_SEQ_STATUS status;
+ pagetable_iterator i;
PagetableEntry *page;
int npages;
int nchunks;
MemoryContextAlloc(tbm->mcxt,
tbm->nchunks * sizeof(PagetableEntry *));
- hash_seq_init(&status, tbm->pagetable);
npages = nchunks = 0;
- while ((page = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ pagetable_start_iterate(tbm->pagetable, &i);
+ while ((page = pagetable_iterate(tbm->pagetable, &i)) != NULL)
{
if (page->ischunk)
tbm->schunks[nchunks++] = page;
return page;
}
- page = (PagetableEntry *) hash_search(tbm->pagetable,
- (void *) &pageno,
- HASH_FIND, NULL);
+ page = pagetable_lookup(tbm->pagetable, pageno);
if (page == NULL)
return NULL;
if (page->ischunk)
}
/* Look up or create an entry */
- page = (PagetableEntry *) hash_search(tbm->pagetable,
- (void *) &pageno,
- HASH_ENTER, &found);
+ page = pagetable_insert(tbm->pagetable, pageno, &found);
}
/* Initialize it if not present before */
if (!found)
{
+ char oldstatus = page->status;
+
MemSet(page, 0, sizeof(PagetableEntry));
+ page->status = oldstatus;
page->blockno = pageno;
/* must count it too */
tbm->nentries++;
bitno = pageno % PAGES_PER_CHUNK;
chunk_pageno = pageno - bitno;
- page = (PagetableEntry *) hash_search(tbm->pagetable,
- (void *) &chunk_pageno,
- HASH_FIND, NULL);
+
+ page = pagetable_lookup(tbm->pagetable, chunk_pageno);
+
if (page != NULL && page->ischunk)
{
int wordnum = WORDNUM(bitno);
*/
if (bitno != 0)
{
- if (hash_search(tbm->pagetable,
- (void *) &pageno,
- HASH_REMOVE, NULL) != NULL)
+ if (pagetable_delete(tbm->pagetable, pageno))
{
/* It was present, so adjust counts */
tbm->nentries--;
}
/* Look up or create entry for chunk-header page */
- page = (PagetableEntry *) hash_search(tbm->pagetable,
- (void *) &chunk_pageno,
- HASH_ENTER, &found);
+ page = pagetable_insert(tbm->pagetable, chunk_pageno, &found);
/* Initialize it if not present before */
if (!found)
{
+ char oldstatus = page->status;
+
MemSet(page, 0, sizeof(PagetableEntry));
+ page->status = oldstatus;
page->blockno = chunk_pageno;
page->ischunk = true;
/* must count it too */
}
else if (!page->ischunk)
{
+ char oldstatus = page->status;
+
/* chunk header page was formerly non-lossy, make it lossy */
MemSet(page, 0, sizeof(PagetableEntry));
+ page->status = oldstatus;
page->blockno = chunk_pageno;
page->ischunk = true;
/* we assume it had some tuple bit(s) set, so mark it lossy */
static void
tbm_lossify(TIDBitmap *tbm)
{
- HASH_SEQ_STATUS status;
+ pagetable_iterator i;
PagetableEntry *page;
/*
Assert(!tbm->iterating);
Assert(tbm->status == TBM_HASH);
- hash_seq_init(&status, tbm->pagetable);
- while ((page = (PagetableEntry *) hash_seq_search(&status)) != NULL)
+ pagetable_start_iterate_at(tbm->pagetable, &i, tbm->lossify_start);
+ while ((page = pagetable_iterate(tbm->pagetable, &i)) != NULL)
{
if (page->ischunk)
continue; /* already a chunk header */
if (tbm->nentries <= tbm->maxentries / 2)
{
- /* we have done enough */
- hash_seq_term(&status);
+ /*
+ * We have made enough room. Remember where to start lossifying
+ * next round, so we evenly iterate over the hashtable.
+ */
+ tbm->lossify_start = i.cur;
break;
}
/*
* Note: tbm_mark_page_lossy may have inserted a lossy chunk into the
- * hashtable. We can continue the same seq_search scan since we do
- * not care whether we visit lossy chunks or not.
+ * hashtable and may have deleted the non-lossy chunk. We can
+ * continue the same hash table scan, since failure to visit one
+ * element or visiting the newly inserted element, isn't fatal.
*/
}
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