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Cleanup and performance enhancements for mini-lookaside.

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FossilOrigin-Name: 74805668430051032ae9b256c84e252755ee03075fc08293c948675ed40ec280
This commit is contained in:
drh
2019-12-13 15:48:21 +00:00
parent ee5b6dd393
commit e6068027ca
6 changed files with 112 additions and 52 deletions
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30
src/sqliteInt.h
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@@ -1277,6 +1277,25 @@ struct Schema {
** disables lookaside without adding a new test for the bDisable flag
** in a performance-critical path. sz should be set by to szTrue whenever
** bDisable changes back to zero.
**
** Lookaside buffers are initially held on the pInit list. As they are
** used and freed, they are added back to the pFree list. New allocations
** come off of pFree first, then pInit as a fallback. This dual-list
** allows use to compute a high-water mark - the maximum number of allocations
** outstanding at any point in the past - by subtracting the number of
** allocations on the pInit list from the total number of allocations.
**
** Enhancement on 2019-12-12: Mini-lookaside
** The default lookaside configuration is 100 slots of 1200 bytes each.
** The larger slot sizes are important for performance, but they waste
** a lot of space, as most lookaside allocations are less than 128 bytes.
** The mini-lookaside enhancement breaks up the lookaside allocation into
** two pools: One of 128-byte slots and the other of the default size
** (1200-byte) slots. Allocations are filled from the mini-pool first,
** failing over to the full-size pool if that does not work. Thus more
** lookaside slots are available while also using less memory.
** This enhancement can be omitted by compiling with
** SQLITE_OMIT_MINI_LOOKASIDE.
*/
struct Lookaside {
u32 bDisable; /* Only operate the lookaside when zero */
@@ -1290,8 +1309,9 @@ struct Lookaside {
#ifndef SQLITE_OMIT_MINI_LOOKASIDE
LookasideSlot *pMiniInit; /* List of mini buffers not prediously used */
LookasideSlot *pMiniFree; /* List of available mini buffers */
void *pMiddle; /* An address between the fullsize and mini buffers */
#endif
void *pMiddle; /* First byte past end of full-size buffers and
** the first byte of mini-buffers */
#endif /* SQLITE_OMIT_MINI_LOOKASIDE */
void *pStart; /* First byte of available memory space */
void *pEnd; /* First byte past end of available space */
};
@@ -1304,7 +1324,11 @@ struct LookasideSlot {
db->lookaside.sz=db->lookaside.bDisable?0:db->lookaside.szTrue
/* Size of the MINI lookside allocation */
#define MINI_SZ 128
#ifdef SQLITE_OMIT_MINI_LOOKASIDE
# define MINI_SZ 0
#else
# define MINI_SZ 128
#endif
/*
** A hash table for built-in function definitions. (Application-defined