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Code Activity

Clean up manipulations of hash indexes' hasho_flag field.

Browse Source 
Standardize on testing a hash index page's type by doing
	(opaque->hasho_flag & LH_PAGE_TYPE) == LH_xxx_PAGE
Various places were taking shortcuts like
	opaque->hasho_flag & LH_BUCKET_PAGE
which while not actually wrong, is still bad practice because
it encourages use of
	opaque->hasho_flag & LH_UNUSED_PAGE
which *is* wrong (LH_UNUSED_PAGE == 0, so the above is constant false).
hash_xlog.c's hash_mask() contained such an incorrect test.

This also ensures that we mask out the additional flag bits that
hasho_flag has accreted since 9.6.  pgstattuple's pgstat_hash_page(),
for one, was failing to do that and was thus actively broken.

Also fix assorted comments that hadn't been updated to reflect the
extended usage of hasho_flag, and fix some macros that were testing
just "(hasho_flag & bit)" to use the less dangerous, project-approved
form "((hasho_flag & bit) != 0)".

Coverity found the bug in hash_mask(); I noted the one in
pgstat_hash_page() through code reading.
This commit is contained in:
Tom Lane
2017-04-14 17:04:25 -04:00
parent 1dffabed49
commit 2040bb4a0b
6 changed files with 29 additions and 25 deletions
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26
src/include/access/hash.h
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@@ -41,13 +41,13 @@ typedef uint32 Bucket;
/*
* Special space for hash index pages.
*
* hasho_flag tells us which type of page we're looking at. For
* example, knowing overflow pages from bucket pages is necessary
* information when you're deleting tuples from a page. If all the
* tuples are deleted from an overflow page, the overflow is made
* available to other buckets by calling _hash_freeovflpage(). If all
* the tuples are deleted from a bucket page, no additional action is
* necessary.
* hasho_flag's LH_PAGE_TYPE bits tell us which type of page we're looking at.
* Additional bits in the flag word are used for more transient purposes.
*
* To test a page's type, do (hasho_flag & LH_PAGE_TYPE) == LH_xxx_PAGE.
* However, we ensure that each used page type has a distinct bit so that
* we can OR together page types for uses such as the allowable-page-types
* argument of _hash_checkpage().
*/
#define LH_UNUSED_PAGE (0)
#define LH_OVERFLOW_PAGE (1 << 0)
@@ -60,7 +60,7 @@ typedef uint32 Bucket;
#define LH_PAGE_HAS_DEAD_TUPLES (1 << 7)
#define LH_PAGE_TYPE \
(LH_OVERFLOW_PAGE|LH_BUCKET_PAGE|LH_BITMAP_PAGE|LH_META_PAGE)
(LH_OVERFLOW_PAGE | LH_BUCKET_PAGE | LH_BITMAP_PAGE | LH_META_PAGE)
/*
* In an overflow page, hasho_prevblkno stores the block number of the previous
@@ -78,16 +78,16 @@ typedef struct HashPageOpaqueData
BlockNumber hasho_prevblkno; /* see above */
BlockNumber hasho_nextblkno; /* see above */
Bucket hasho_bucket; /* bucket number this pg belongs to */
uint16 hasho_flag; /* page type code, see above */
uint16 hasho_flag; /* page type code + flag bits, see above */
uint16 hasho_page_id; /* for identification of hash indexes */
} 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)
#define H_HAS_DEAD_TUPLES(opaque) ((opaque)->hasho_flag & LH_PAGE_HAS_DEAD_TUPLES)
#define H_NEEDS_SPLIT_CLEANUP(opaque) (((opaque)->hasho_flag & LH_BUCKET_NEEDS_SPLIT_CLEANUP) != 0)
#define H_BUCKET_BEING_SPLIT(opaque) (((opaque)->hasho_flag & LH_BUCKET_BEING_SPLIT) != 0)
#define H_BUCKET_BEING_POPULATED(opaque) (((opaque)->hasho_flag & LH_BUCKET_BEING_POPULATED) != 0)
#define H_HAS_DEAD_TUPLES(opaque) (((opaque)->hasho_flag & LH_PAGE_HAS_DEAD_TUPLES) != 0)
/*
* The page ID is for the convenience of pg_filedump and similar utilities,