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4b31063643
Some code in DiscreteKnapsack() attempted to zero all words in a
Bitmapset by performing bms_del_members() to delete all the members from
itself before replacing those members with members from another set.
When that code was written, this was a valid way to manipulate the set
in such a way to save from palloc having to be called to allocate a new
Bitmapset. However, 00b41463c modified Bitmapsets so that an empty set is
*always* represented as NULL and this breaks the optimization as the
Bitmapset code will always pfree the memory when the set becomes empty.
Since DiscreteKnapsack() has been coded to avoid as many unneeded
allocations as possible, it seems risky to not fix this. Here we add
bms_replace_members() to effectively perform an in-place copy of another
set, reusing the memory of the existing set, when possible.
This got broken in v16, but no backpatch for now as there've been no
complaints.
Reviewed-by: Richard Guo
Discussion: https://postgr.es/m/CAApHDvoTCBkBU2PJghNOFUiO0q=QP4WAWHi5sJP6_4=b2WodrA@mail.gmail.com
127 lines
4.4 KiB
C
127 lines
4.4 KiB
C
/*-------------------------------------------------------------------------
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*
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* bitmapset.h
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* PostgreSQL generic bitmap set package
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*
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* A bitmap set can represent any set of nonnegative integers, although
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* it is mainly intended for sets where the maximum value is not large,
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* say at most a few hundred. By convention, we always represent the
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* empty set by a NULL pointer.
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*
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*
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* Copyright (c) 2003-2024, PostgreSQL Global Development Group
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*
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* src/include/nodes/bitmapset.h
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef BITMAPSET_H
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#define BITMAPSET_H
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#include "nodes/nodes.h"
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/*
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* Forward decl to save including pg_list.h
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*/
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struct List;
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/*
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* Data representation
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*
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* Larger bitmap word sizes generally give better performance, so long as
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* they're not wider than the processor can handle efficiently. We use
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* 64-bit words if pointers are that large, else 32-bit words.
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*/
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#if SIZEOF_VOID_P >= 8
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#define BITS_PER_BITMAPWORD 64
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typedef uint64 bitmapword; /* must be an unsigned type */
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typedef int64 signedbitmapword; /* must be the matching signed type */
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#else
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#define BITS_PER_BITMAPWORD 32
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typedef uint32 bitmapword; /* must be an unsigned type */
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typedef int32 signedbitmapword; /* must be the matching signed type */
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#endif
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typedef struct Bitmapset
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{
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pg_node_attr(custom_copy_equal, special_read_write, no_query_jumble)
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NodeTag type;
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int nwords; /* number of words in array */
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bitmapword words[FLEXIBLE_ARRAY_MEMBER]; /* really [nwords] */
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} Bitmapset;
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/* result of bms_subset_compare */
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typedef enum
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{
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BMS_EQUAL, /* sets are equal */
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BMS_SUBSET1, /* first set is a subset of the second */
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BMS_SUBSET2, /* second set is a subset of the first */
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BMS_DIFFERENT, /* neither set is a subset of the other */
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} BMS_Comparison;
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/* result of bms_membership */
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typedef enum
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{
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BMS_EMPTY_SET, /* 0 members */
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BMS_SINGLETON, /* 1 member */
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BMS_MULTIPLE, /* >1 member */
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} BMS_Membership;
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/*
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* function prototypes in nodes/bitmapset.c
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*/
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extern Bitmapset *bms_copy(const Bitmapset *a);
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extern bool bms_equal(const Bitmapset *a, const Bitmapset *b);
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extern int bms_compare(const Bitmapset *a, const Bitmapset *b);
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extern Bitmapset *bms_make_singleton(int x);
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extern void bms_free(Bitmapset *a);
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extern Bitmapset *bms_union(const Bitmapset *a, const Bitmapset *b);
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extern Bitmapset *bms_intersect(const Bitmapset *a, const Bitmapset *b);
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extern Bitmapset *bms_difference(const Bitmapset *a, const Bitmapset *b);
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extern bool bms_is_subset(const Bitmapset *a, const Bitmapset *b);
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extern BMS_Comparison bms_subset_compare(const Bitmapset *a, const Bitmapset *b);
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extern bool bms_is_member(int x, const Bitmapset *a);
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extern int bms_member_index(Bitmapset *a, int x);
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extern bool bms_overlap(const Bitmapset *a, const Bitmapset *b);
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extern bool bms_overlap_list(const Bitmapset *a, const struct List *b);
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extern bool bms_nonempty_difference(const Bitmapset *a, const Bitmapset *b);
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extern int bms_singleton_member(const Bitmapset *a);
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extern bool bms_get_singleton_member(const Bitmapset *a, int *member);
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extern int bms_num_members(const Bitmapset *a);
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/* optimized tests when we don't need to know exact membership count: */
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extern BMS_Membership bms_membership(const Bitmapset *a);
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/* NULL is now the only allowed representation of an empty bitmapset */
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#define bms_is_empty(a) ((a) == NULL)
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/* these routines recycle (modify or free) their non-const inputs: */
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extern Bitmapset *bms_add_member(Bitmapset *a, int x);
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extern Bitmapset *bms_del_member(Bitmapset *a, int x);
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extern Bitmapset *bms_add_members(Bitmapset *a, const Bitmapset *b);
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extern Bitmapset *bms_replace_members(Bitmapset *a, const Bitmapset *b);
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extern Bitmapset *bms_add_range(Bitmapset *a, int lower, int upper);
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extern Bitmapset *bms_int_members(Bitmapset *a, const Bitmapset *b);
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extern Bitmapset *bms_del_members(Bitmapset *a, const Bitmapset *b);
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extern Bitmapset *bms_join(Bitmapset *a, Bitmapset *b);
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/* support for iterating through the integer elements of a set: */
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extern int bms_next_member(const Bitmapset *a, int prevbit);
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extern int bms_prev_member(const Bitmapset *a, int prevbit);
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/* support for hashtables using Bitmapsets as keys: */
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extern uint32 bms_hash_value(const Bitmapset *a);
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extern uint32 bitmap_hash(const void *key, Size keysize);
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extern int bitmap_match(const void *key1, const void *key2, Size keysize);
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#endif /* BITMAPSET_H */
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