diff options
Diffstat (limited to 'src/backend/access/hash/hashpage.c')
| -rw-r--r-- | src/backend/access/hash/hashpage.c | 49 |
1 files changed, 36 insertions, 13 deletions
diff --git a/src/backend/access/hash/hashpage.c b/src/backend/access/hash/hashpage.c index d1b3aaa2325..b8c520e3c0d 100644 --- a/src/backend/access/hash/hashpage.c +++ b/src/backend/access/hash/hashpage.c @@ -8,7 +8,7 @@ * * * IDENTIFICATION - * $Header: /cvsroot/pgsql/src/backend/access/hash/hashpage.c,v 1.31 2001/06/27 23:31:37 tgl Exp $ + * $Header: /cvsroot/pgsql/src/backend/access/hash/hashpage.c,v 1.32 2001/07/15 22:48:15 tgl Exp $ * * NOTES * Postgres hash pages look like ordinary relation pages. The opaque @@ -18,7 +18,7 @@ * address of the page if it is an overflow page. * * The first page in a hash relation, page zero, is special -- it stores - * information describing the hash table; it is referred to as teh + * information describing the hash table; it is referred to as the * "meta page." Pages one and higher store the actual data. * *------------------------------------------------------------------------- @@ -48,6 +48,19 @@ static void _hash_splitpage(Relation rel, Buffer metabuf, Bucket obucket, Bucket * before the lock table is fully initialized, so we can't use it. * Strictly speaking, this violates 2pl, but we don't do 2pl on the * system catalogs anyway. + * + * Note that our page locks are actual lockmanager locks, not buffer + * locks (as are used by btree, for example). This is a good idea because + * the algorithms are not deadlock-free, and we'd better be able to detect + * and recover from deadlocks. + * + * Another important difference from btree is that a hash indexscan + * retains both a lock and a buffer pin on the current index page + * between hashgettuple() calls (btree keeps only a buffer pin). + * Because of this, it's safe to do item deletions with only a regular + * write lock on a hash page --- there cannot be an indexscan stopped on + * the page being deleted, other than an indexscan of our own backend, + * which will be taken care of by _hash_adjscans. */ @@ -350,6 +363,16 @@ _hash_unsetpagelock(Relation rel, } } +/* + * Delete a hash index item. + * + * It is safe to delete an item after acquiring a regular WRITE lock on + * the page, because no other backend can hold a READ lock on the page, + * and that means no other backend currently has an indexscan stopped on + * any item of the item being deleted. Our own backend might have such + * an indexscan (in fact *will*, since that's how VACUUM found the item + * in the first place), but _hash_adjscans will fix the scan position. + */ void _hash_pagedel(Relation rel, ItemPointer tid) { @@ -384,7 +407,7 @@ _hash_pagedel(Relation rel, ItemPointer tid) metabuf = _hash_getbuf(rel, HASH_METAPAGE, HASH_WRITE); metap = (HashMetaPage) BufferGetPage(metabuf); _hash_checkpage((Page) metap, LH_META_PAGE); - ++metap->hashm_nkeys; + metap->hashm_nkeys--; _hash_wrtbuf(rel, metabuf); } @@ -402,32 +425,32 @@ _hash_expandtable(Relation rel, Buffer metabuf) _hash_checkpage((Page) metap, LH_META_PAGE); metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE); - new_bucket = ++metap->MAX_BUCKET; + new_bucket = ++metap->hashm_maxbucket; metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ); - old_bucket = (metap->MAX_BUCKET & metap->LOW_MASK); + old_bucket = (metap->hashm_maxbucket & metap->hashm_lowmask); /* - * If the split point is increasing (MAX_BUCKET's log base 2 * + * If the split point is increasing (hashm_maxbucket's log base 2 * * increases), we need to copy the current contents of the spare split * bucket to the next bucket. */ - spare_ndx = _hash_log2(metap->MAX_BUCKET + 1); - if (spare_ndx > metap->OVFL_POINT) + spare_ndx = _hash_log2(metap->hashm_maxbucket + 1); + if (spare_ndx > metap->hashm_ovflpoint) { metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE); - metap->SPARES[spare_ndx] = metap->SPARES[metap->OVFL_POINT]; - metap->OVFL_POINT = spare_ndx; + metap->hashm_spares[spare_ndx] = metap->hashm_spares[metap->hashm_ovflpoint]; + metap->hashm_ovflpoint = spare_ndx; metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ); } - if (new_bucket > metap->HIGH_MASK) + if (new_bucket > metap->hashm_highmask) { /* Starting a new doubling */ metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_READ, HASH_WRITE); - metap->LOW_MASK = metap->HIGH_MASK; - metap->HIGH_MASK = new_bucket | metap->LOW_MASK; + metap->hashm_lowmask = metap->hashm_highmask; + metap->hashm_highmask = new_bucket | metap->hashm_lowmask; metap = (HashMetaPage) _hash_chgbufaccess(rel, &metabuf, HASH_WRITE, HASH_READ); } |