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Postgres FD Implementation
Commit 86482e17 authored by Tom Lane's avatar Tom Lane
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Correct serious bug in hashtable expansion routine: under the 

right circumstances it would leave old and new bucket headers pointing to
the same list of records.
parent 7f79496a
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Showing with 44 additions and 38 deletions
src/backend/utils/hash/dynahash.c
View file @ 86482e17
......@@ -7,7 +7,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/hash/dynahash.c,v 1.22 1999/05/25 16:12:28 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/hash/dynahash.c,v 1.23 1999/05/31 17:01:52 tgl Exp $
*
*-------------------------------------------------------------------------
*/
......@@ -52,25 +52,23 @@
#include "utils/memutils.h"
/*
* Fast arithmetic, relying on powers of 2,
* and on pre-processor concatenation property
* Fast MOD arithmetic, assuming that y is a power of 2 !
*/
#define MOD(x,y) ((x) & ((y)-1))
/*
* external routines
*/
/*
* Private function prototypes
*/
static long *DynaHashAlloc(unsigned int size);
static void DynaHashFree(Pointer ptr);
static uint32 call_hash(HTAB *hashp, char *k, int len);
static uint32 call_hash(HTAB *hashp, char *k);
static SEG_OFFSET seg_alloc(HTAB *hashp);
static int bucket_alloc(HTAB *hashp);
static int dir_realloc(HTAB *hashp);
static int expand_table(HTAB *hashp);
static int hdefault(HTAB *hashp);
static int init_htab(HTAB *hashp, int nelem);
typedef long *((*dhalloc_ptr) ());
......@@ -118,15 +116,6 @@ DynaHashFree(Pointer ptr)
#endif /* FRONTEND */
/* ----------------
* Internal routines
* ----------------
*/
static int expand_table(HTAB *hashp);
static int hdefault(HTAB *hashp);
static int init_htab(HTAB *hashp, int nelem);
/*
* pointer access macros. Shared memory implementation cannot
......@@ -220,6 +209,8 @@ hash_create(int nelem, HASHCTL *info, int flags)
{
hctl->ssize = info->ssize;
hctl->sshift = my_log2(info->ssize);
/* ssize had better be a power of 2 */
Assert(hctl->ssize == (1L << hctl->sshift));
}
if (flags & HASH_FFACTOR)
hctl->ffactor = info->ffactor;
......@@ -412,6 +403,8 @@ hash_estimate_size(long num_entries, long keysize, long datasize)
* XXX this sure looks thoroughly broken to me --- tgl 2/99.
* It's freeing every entry individually --- but they weren't
* allocated individually, see bucket_alloc!! Why doesn't it crash?
* ANSWER: it probably does crash, but is never invoked in normal
* operations...
*/
void
......@@ -479,14 +472,13 @@ hash_stats(char *where, HTAB *hashp)
/*******************************SEARCH ROUTINES *****************************/
static uint32
call_hash(HTAB *hashp, char *k, int len)
call_hash(HTAB *hashp, char *k)
{
HHDR *hctl = hashp->hctl;
long hash_val,
bucket;
HHDR *hctl;
hctl = hashp->hctl;
hash_val = hashp->hash(k, len);
hash_val = hashp->hash(k, (int) hctl->keysize);
bucket = hash_val & hctl->high_mask;
if (bucket > hctl->max_bucket)
......@@ -550,9 +542,9 @@ hash_search(HTAB *hashp,
}
else
{
bucket = call_hash(hashp, keyPtr, hctl->keysize);
bucket = call_hash(hashp, keyPtr);
segment_num = bucket >> hctl->sshift;
segment_ndx = bucket & (hctl->ssize - 1);
segment_ndx = MOD(bucket, hctl->ssize);
segp = GET_SEG(hashp, segment_num);
......@@ -598,8 +590,10 @@ hash_search(HTAB *hashp,
Assert(hctl->nkeys > 0);
hctl->nkeys--;
/* add the bucket to the freelist for this table. */
/* remove record from hash bucket's chain. */
*prevIndexPtr = curr->next;
/* add the record to the freelist for this table. */
curr->next = hctl->freeBucketIndex;
hctl->freeBucketIndex = currIndex;
......@@ -639,7 +633,6 @@ hash_search(HTAB *hashp,
currIndex = hctl->freeBucketIndex;
if (currIndex == INVALID_INDEX)
{
/* no free elements. allocate another chunk of buckets */
if (!bucket_alloc(hashp))
return NULL;
......@@ -722,7 +715,7 @@ hash_seq(HTAB *hashp)
* initialize the search within this bucket.
*/
segment_num = curBucket >> hctl->sshift;
segment_ndx = curBucket & (hctl->ssize - 1);
segment_ndx = MOD(curBucket, hctl->ssize);
/*
* first find the right segment in the table directory.
......@@ -751,6 +744,10 @@ hash_seq(HTAB *hashp)
/********************************* UTILITIES ************************/
/*
* Expand the table by adding one more hash bucket.
*/
static int
expand_table(HTAB *hashp)
{
......@@ -790,19 +787,31 @@ expand_table(HTAB *hashp)
hctl->nsegs++;
}
/* OK, we got a new bucket */
/* OK, we created a new bucket */
hctl->max_bucket++;
old_bucket = (hctl->max_bucket & hctl->low_mask);
/*
* *Before* changing masks, find old bucket corresponding to same hash
* values; values in that bucket may need to be relocated to new bucket.
* Note that new_bucket is certainly larger than low_mask at this point,
* so we can skip the first step of the regular hash mask calc.
*/
old_bucket = (new_bucket & hctl->low_mask);
/*
* If we crossed a power of 2, readjust masks.
*/
if (new_bucket > hctl->high_mask)
{
/* Starting a new doubling */
hctl->low_mask = hctl->high_mask;
hctl->high_mask = new_bucket | hctl->low_mask;
}
/*
* Relocate records to the new bucket
* Relocate records to the new bucket. NOTE: because of the way the
* hash masking is done in call_hash, only one old bucket can need to
* be split at this point. With a different way of reducing the hash
* value, that might not be true!
*/
old_segnum = old_bucket >> hctl->sshift;
old_segndx = MOD(old_bucket, hctl->ssize);
......@@ -816,12 +825,9 @@ expand_table(HTAB *hashp)
chainIndex != INVALID_INDEX;
chainIndex = nextIndex)
{
chain = GET_BUCKET(hashp, chainIndex);
nextIndex = chain->next;
if (call_hash(hashp,
(char *) &(chain->key),
hctl->keysize) == old_bucket)
if (call_hash(hashp, (char *) &(chain->key)) == old_bucket)
{
*old = chainIndex;
old = &chain->next;
......@@ -831,8 +837,10 @@ expand_table(HTAB *hashp)
*newbi = chainIndex;
newbi = &chain->next;
}
chain->next = INVALID_INDEX;
}
/* don't forget to terminate the rebuilt hash chains... */
*old = INVALID_INDEX;
*newbi = INVALID_INDEX;
return 1;
}
......@@ -907,15 +915,13 @@ bucket_alloc(HTAB *hashp)
/* make sure its aligned correctly */
bucketSize = MAXALIGN(bucketSize);
/*
* tmpIndex is the shmem offset into the first bucket of the array.
*/
tmpBucket = (ELEMENT *)
hashp->alloc((unsigned long) BUCKET_ALLOC_INCR * bucketSize);
if (!tmpBucket)
return 0;
/* tmpIndex is the shmem offset into the first bucket of the array */
tmpIndex = MAKE_HASHOFFSET(hashp, tmpBucket);
/* set the freebucket list to point to the first bucket */
......
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