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.
This commit is contained in:
Tom Lane
parent
7f79496aa5
commit
86482e17bd
@ -7,7 +7,7 @@
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*
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*
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* IDENTIFICATION
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* $Header: /cvsroot/pgsql/src/backend/utils/hash/dynahash.c,v 1.22 1999/05/25 16:12:28 momjian Exp $
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* $Header: /cvsroot/pgsql/src/backend/utils/hash/dynahash.c,v 1.23 1999/05/31 17:01:52 tgl Exp $
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*
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*-------------------------------------------------------------------------
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*/
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@ -52,25 +52,23 @@
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#include "utils/memutils.h"
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/*
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* Fast arithmetic, relying on powers of 2,
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* and on pre-processor concatenation property
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* Fast MOD arithmetic, assuming that y is a power of 2 !
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*/
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#define MOD(x,y) ((x) & ((y)-1))
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/*
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* external routines
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*/
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/*
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* Private function prototypes
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*/
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static long *DynaHashAlloc(unsigned int size);
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static void DynaHashFree(Pointer ptr);
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static uint32 call_hash(HTAB *hashp, char *k, int len);
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static uint32 call_hash(HTAB *hashp, char *k);
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static SEG_OFFSET seg_alloc(HTAB *hashp);
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static int bucket_alloc(HTAB *hashp);
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static int dir_realloc(HTAB *hashp);
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static int expand_table(HTAB *hashp);
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static int hdefault(HTAB *hashp);
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static int init_htab(HTAB *hashp, int nelem);
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typedef long *((*dhalloc_ptr) ());
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@ -118,15 +116,6 @@ DynaHashFree(Pointer ptr)
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#endif /* FRONTEND */
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/* ----------------
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* Internal routines
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* ----------------
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*/
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static int expand_table(HTAB *hashp);
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static int hdefault(HTAB *hashp);
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static int init_htab(HTAB *hashp, int nelem);
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/*
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* pointer access macros. Shared memory implementation cannot
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@ -220,6 +209,8 @@ hash_create(int nelem, HASHCTL *info, int flags)
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{
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hctl->ssize = info->ssize;
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hctl->sshift = my_log2(info->ssize);
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/* ssize had better be a power of 2 */
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Assert(hctl->ssize == (1L << hctl->sshift));
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}
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if (flags & HASH_FFACTOR)
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hctl->ffactor = info->ffactor;
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@ -412,6 +403,8 @@ hash_estimate_size(long num_entries, long keysize, long datasize)
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* XXX this sure looks thoroughly broken to me --- tgl 2/99.
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* It's freeing every entry individually --- but they weren't
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* allocated individually, see bucket_alloc!! Why doesn't it crash?
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* ANSWER: it probably does crash, but is never invoked in normal
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* operations...
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*/
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void
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@ -479,14 +472,13 @@ hash_stats(char *where, HTAB *hashp)
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/*******************************SEARCH ROUTINES *****************************/
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static uint32
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call_hash(HTAB *hashp, char *k, int len)
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call_hash(HTAB *hashp, char *k)
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{
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HHDR *hctl = hashp->hctl;
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long hash_val,
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bucket;
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HHDR *hctl;
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hctl = hashp->hctl;
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hash_val = hashp->hash(k, len);
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hash_val = hashp->hash(k, (int) hctl->keysize);
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bucket = hash_val & hctl->high_mask;
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if (bucket > hctl->max_bucket)
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@ -550,9 +542,9 @@ hash_search(HTAB *hashp,
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}
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else
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{
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bucket = call_hash(hashp, keyPtr, hctl->keysize);
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bucket = call_hash(hashp, keyPtr);
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segment_num = bucket >> hctl->sshift;
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segment_ndx = bucket & (hctl->ssize - 1);
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segment_ndx = MOD(bucket, hctl->ssize);
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segp = GET_SEG(hashp, segment_num);
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@ -598,8 +590,10 @@ hash_search(HTAB *hashp,
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Assert(hctl->nkeys > 0);
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hctl->nkeys--;
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/* add the bucket to the freelist for this table. */
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/* remove record from hash bucket's chain. */
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*prevIndexPtr = curr->next;
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/* add the record to the freelist for this table. */
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curr->next = hctl->freeBucketIndex;
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hctl->freeBucketIndex = currIndex;
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@ -639,7 +633,6 @@ hash_search(HTAB *hashp,
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currIndex = hctl->freeBucketIndex;
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if (currIndex == INVALID_INDEX)
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{
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/* no free elements. allocate another chunk of buckets */
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if (!bucket_alloc(hashp))
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return NULL;
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@ -722,7 +715,7 @@ hash_seq(HTAB *hashp)
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* initialize the search within this bucket.
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*/
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segment_num = curBucket >> hctl->sshift;
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segment_ndx = curBucket & (hctl->ssize - 1);
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segment_ndx = MOD(curBucket, hctl->ssize);
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/*
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* first find the right segment in the table directory.
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@ -751,6 +744,10 @@ hash_seq(HTAB *hashp)
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/********************************* UTILITIES ************************/
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/*
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* Expand the table by adding one more hash bucket.
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*/
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static int
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expand_table(HTAB *hashp)
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{
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@ -790,19 +787,31 @@ expand_table(HTAB *hashp)
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hctl->nsegs++;
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}
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/* OK, we got a new bucket */
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/* OK, we created a new bucket */
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hctl->max_bucket++;
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old_bucket = (hctl->max_bucket & hctl->low_mask);
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/*
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* *Before* changing masks, find old bucket corresponding to same hash
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* values; values in that bucket may need to be relocated to new bucket.
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* Note that new_bucket is certainly larger than low_mask at this point,
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* so we can skip the first step of the regular hash mask calc.
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*/
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old_bucket = (new_bucket & hctl->low_mask);
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/*
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* If we crossed a power of 2, readjust masks.
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*/
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if (new_bucket > hctl->high_mask)
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{
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/* Starting a new doubling */
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hctl->low_mask = hctl->high_mask;
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hctl->high_mask = new_bucket | hctl->low_mask;
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}
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/*
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* Relocate records to the new bucket
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* Relocate records to the new bucket. NOTE: because of the way the
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* hash masking is done in call_hash, only one old bucket can need to
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* be split at this point. With a different way of reducing the hash
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* value, that might not be true!
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*/
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old_segnum = old_bucket >> hctl->sshift;
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old_segndx = MOD(old_bucket, hctl->ssize);
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@ -816,12 +825,9 @@ expand_table(HTAB *hashp)
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chainIndex != INVALID_INDEX;
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chainIndex = nextIndex)
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{
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chain = GET_BUCKET(hashp, chainIndex);
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nextIndex = chain->next;
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if (call_hash(hashp,
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(char *) &(chain->key),
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hctl->keysize) == old_bucket)
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if (call_hash(hashp, (char *) &(chain->key)) == old_bucket)
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{
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*old = chainIndex;
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old = &chain->next;
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@ -831,8 +837,10 @@ expand_table(HTAB *hashp)
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*newbi = chainIndex;
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newbi = &chain->next;
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}
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chain->next = INVALID_INDEX;
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}
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/* don't forget to terminate the rebuilt hash chains... */
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*old = INVALID_INDEX;
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*newbi = INVALID_INDEX;
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return 1;
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}
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@ -907,15 +915,13 @@ bucket_alloc(HTAB *hashp)
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/* make sure its aligned correctly */
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bucketSize = MAXALIGN(bucketSize);
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/*
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* tmpIndex is the shmem offset into the first bucket of the array.
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*/
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tmpBucket = (ELEMENT *)
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hashp->alloc((unsigned long) BUCKET_ALLOC_INCR * bucketSize);
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if (!tmpBucket)
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return 0;
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/* tmpIndex is the shmem offset into the first bucket of the array */
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tmpIndex = MAKE_HASHOFFSET(hashp, tmpBucket);
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/* set the freebucket list to point to the first bucket */
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