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Improve hash index bucket split behavior.

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Previously, the right to split a bucket was represented by a
heavyweight lock on the page number of the primary bucket page.
Unfortunately, this meant that every scan needed to take a heavyweight
lock on that bucket also, which was bad for concurrency.  Instead, use
a cleanup lock on the primary bucket page to indicate the right to
begin a split, so that scans only need to retain a pin on that page,
which is they would have to acquire anyway, and which is also much
cheaper.

In addition to reducing the locking cost, this also avoids locking out
scans and inserts for the entire lifetime of the split: while the new
bucket is being populated with copies of the appropriate tuples from
the old bucket, scans and inserts can happen in parallel.  There are
minor concurrency improvements for vacuum operations as well, though
the situation there is still far from ideal.

This patch also removes the unworldly assumption that a split will
never be interrupted.  With the new code, a split is done in a series
of small steps and the system can pick up where it left off if it is
interrupted prior to completion.  While this patch does not itself add
write-ahead logging for hash indexes, it is clearly a necessary first
step, since one of the things that could interrupt a split is the
removal of electrical power from the machine performing it.

Amit Kapila.  I wrote the original design on which this patch is
based, and did a good bit of work on the comments and README through
multiple rounds of review, but all of the code is Amit's.  Also
reviewed by Jesper Pedersen, Jeff Janes, and others.

Discussion: http://postgr.es/m/CAA4eK1LfzcZYxLoXS874Ad0+S-ZM60U9bwcyiUZx9mHZ-KCWhw@mail.gmail.com
This commit is contained in:
Robert Haas
2016-11-30 15:39:21 -05:00
parent 213c0f2d78
commit 6d46f4783e
12 changed files with 1361 additions and 622 deletions
Download Patch File Download Diff File Expand all files Collapse all files

82
src/include/access/hash.h
View File

@@ -24,6 +24,7 @@
#include "lib/stringinfo.h"
#include "storage/bufmgr.h"
#include "storage/lockdefs.h"
#include "utils/hsearch.h"
#include "utils/relcache.h"
/*
@@ -32,6 +33,8 @@
*/
typedef uint32 Bucket;
#define InvalidBucket ((Bucket) 0xFFFFFFFF)
#define BUCKET_TO_BLKNO(metap,B) \
((BlockNumber) ((B) + ((B) ? (metap)->hashm_spares[_hash_log2((B)+1)-1] : 0)) + 1)
@@ -51,6 +54,9 @@ typedef uint32 Bucket;
#define LH_BUCKET_PAGE (1 << 1)
#define LH_BITMAP_PAGE (1 << 2)
#define LH_META_PAGE (1 << 3)
#define LH_BUCKET_BEING_POPULATED (1 << 4)
#define LH_BUCKET_BEING_SPLIT (1 << 5)
#define LH_BUCKET_NEEDS_SPLIT_CLEANUP (1 << 6)
typedef struct HashPageOpaqueData
{
@@ -63,6 +69,10 @@ typedef struct HashPageOpaqueData
typedef HashPageOpaqueData *HashPageOpaque;
#define H_NEEDS_SPLIT_CLEANUP(opaque) ((opaque)->hasho_flag & LH_BUCKET_NEEDS_SPLIT_CLEANUP)
#define H_BUCKET_BEING_SPLIT(opaque) ((opaque)->hasho_flag & LH_BUCKET_BEING_SPLIT)
#define H_BUCKET_BEING_POPULATED(opaque) ((opaque)->hasho_flag & LH_BUCKET_BEING_POPULATED)
/*
* The page ID is for the convenience of pg_filedump and similar utilities,
* which otherwise would have a hard time telling pages of different index
@@ -79,19 +89,6 @@ typedef struct HashScanOpaqueData
/* Hash value of the scan key, ie, the hash key we seek */
uint32 hashso_sk_hash;
/*
* By definition, a hash scan should be examining only one bucket. We
* record the bucket number here as soon as it is known.
*/
Bucket hashso_bucket;
bool hashso_bucket_valid;
/*
* If we have a share lock on the bucket, we record it here. When
* hashso_bucket_blkno is zero, we have no such lock.
*/
BlockNumber hashso_bucket_blkno;
/*
* We also want to remember which buffer we're currently examining in the
* scan. We keep the buffer pinned (but not locked) across hashgettuple
@@ -100,11 +97,30 @@ typedef struct HashScanOpaqueData
*/
Buffer hashso_curbuf;
/* remember the buffer associated with primary bucket */
Buffer hashso_bucket_buf;
/*
* remember the buffer associated with primary bucket page of bucket being
* split. it is required during the scan of the bucket which is being
* populated during split operation.
*/
Buffer hashso_split_bucket_buf;
/* Current position of the scan, as an index TID */
ItemPointerData hashso_curpos;
/* Current position of the scan, as a heap TID */
ItemPointerData hashso_heappos;
/* Whether scan starts on bucket being populated due to split */
bool hashso_buc_populated;
/*
* Whether scanning bucket being split? The value of this parameter is
* referred only when hashso_buc_populated is true.
*/
bool hashso_buc_split;
} HashScanOpaqueData;
typedef HashScanOpaqueData *HashScanOpaque;
@@ -175,6 +191,8 @@ typedef HashMetaPageData *HashMetaPage;
sizeof(ItemIdData) - \
MAXALIGN(sizeof(HashPageOpaqueData)))
#define INDEX_MOVED_BY_SPLIT_MASK 0x2000
#define HASH_MIN_FILLFACTOR 10
#define HASH_DEFAULT_FILLFACTOR 75
@@ -223,9 +241,6 @@ typedef HashMetaPageData *HashMetaPage;
#define HASH_WRITE BUFFER_LOCK_EXCLUSIVE
#define HASH_NOLOCK (-1)
#define HASH_SHARE ShareLock
#define HASH_EXCLUSIVE ExclusiveLock
/*
* Strategy number. There's only one valid strategy for hashing: equality.
*/
@@ -297,21 +312,21 @@ extern OffsetNumber _hash_pgaddtup(Relation rel, Buffer buf,
Size itemsize, IndexTuple itup);
/* hashovfl.c */
extern Buffer _hash_addovflpage(Relation rel, Buffer metabuf, Buffer buf);
extern BlockNumber _hash_freeovflpage(Relation rel, Buffer ovflbuf,
BufferAccessStrategy bstrategy);
extern Buffer _hash_addovflpage(Relation rel, Buffer metabuf, Buffer buf, bool retain_pin);
extern BlockNumber _hash_freeovflpage(Relation rel, Buffer ovflbuf, Buffer wbuf,
bool wbuf_dirty, BufferAccessStrategy bstrategy);
extern void _hash_initbitmap(Relation rel, HashMetaPage metap,
BlockNumber blkno, ForkNumber forkNum);
extern void _hash_squeezebucket(Relation rel,
Bucket bucket, BlockNumber bucket_blkno,
Buffer bucket_buf,
BufferAccessStrategy bstrategy);
/* hashpage.c */
extern void _hash_getlock(Relation rel, BlockNumber whichlock, int access);
extern bool _hash_try_getlock(Relation rel, BlockNumber whichlock, int access);
extern void _hash_droplock(Relation rel, BlockNumber whichlock, int access);
extern Buffer _hash_getbuf(Relation rel, BlockNumber blkno,
int access, int flags);
extern Buffer _hash_getbuf_with_condlock_cleanup(Relation rel,
BlockNumber blkno, int flags);
extern Buffer _hash_getinitbuf(Relation rel, BlockNumber blkno);
extern Buffer _hash_getnewbuf(Relation rel, BlockNumber blkno,
ForkNumber forkNum);
@@ -320,6 +335,7 @@ extern Buffer _hash_getbuf_with_strategy(Relation rel, BlockNumber blkno,
BufferAccessStrategy bstrategy);
extern void _hash_relbuf(Relation rel, Buffer buf);
extern void _hash_dropbuf(Relation rel, Buffer buf);
extern void _hash_dropscanbuf(Relation rel, HashScanOpaque so);
extern void _hash_wrtbuf(Relation rel, Buffer buf);
extern void _hash_chgbufaccess(Relation rel, Buffer buf, int from_access,
int to_access);
@@ -327,12 +343,9 @@ extern uint32 _hash_metapinit(Relation rel, double num_tuples,
ForkNumber forkNum);
extern void _hash_pageinit(Page page, Size size);
extern void _hash_expandtable(Relation rel, Buffer metabuf);
/* hashscan.c */
extern void _hash_regscan(IndexScanDesc scan);
extern void _hash_dropscan(IndexScanDesc scan);
extern bool _hash_has_active_scan(Relation rel, Bucket bucket);
extern void ReleaseResources_hash(void);
extern void _hash_finish_split(Relation rel, Buffer metabuf, Buffer obuf,
Bucket obucket, uint32 maxbucket, uint32 highmask,
uint32 lowmask);
/* hashsearch.c */
extern bool _hash_next(IndexScanDesc scan, ScanDirection dir);
@@ -362,5 +375,18 @@ extern bool _hash_convert_tuple(Relation index,
Datum *index_values, bool *index_isnull);
extern OffsetNumber _hash_binsearch(Page page, uint32 hash_value);
extern OffsetNumber _hash_binsearch_last(Page page, uint32 hash_value);
extern BlockNumber _hash_get_oldblock_from_newbucket(Relation rel, Bucket new_bucket);
extern BlockNumber _hash_get_newblock_from_oldbucket(Relation rel, Bucket old_bucket);
extern Bucket _hash_get_newbucket_from_oldbucket(Relation rel, Bucket old_bucket,
uint32 lowmask, uint32 maxbucket);
/* hash.c */
extern void hashbucketcleanup(Relation rel, Bucket cur_bucket,
Buffer bucket_buf, BlockNumber bucket_blkno,
BufferAccessStrategy bstrategy,
uint32 maxbucket, uint32 highmask, uint32 lowmask,
double *tuples_removed, double *num_index_tuples,
bool bucket_has_garbage,
IndexBulkDeleteCallback callback, void *callback_state);
#endif /* HASH_H */

2
src/include/access/itup.h
View File

@@ -63,7 +63,7 @@ typedef IndexAttributeBitMapData *IndexAttributeBitMap;
* t_info manipulation macros
*/
#define INDEX_SIZE_MASK 0x1FFF
/* bit 0x2000 is not used at present */
/* bit 0x2000 is reserved for index-AM specific usage */
#define INDEX_VAR_MASK 0x4000
#define INDEX_NULL_MASK 0x8000