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Omit the (undocumented) SQLITE_PCACHE_SEPARATE_HEADER compile-time option.

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FossilOrigin-Name: 60947da687d525e72e62bcddcdf4c5c819818855074cc318c9ee656e83897aef
This commit is contained in:
drh
2022-08-09 14:28:54 +00:00
parent 6aafd74853
commit c8e9f6818b
5 changed files with 26 additions and 42 deletions
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3
src/ctime.c
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@@ -683,9 +683,6 @@ static const char * const sqlite3azCompileOpt[] = {
#ifdef SQLITE_OMIT_XFER_OPT
"OMIT_XFER_OPT",
#endif
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
"PCACHE_SEPARATE_HEADER",
#endif
#ifdef SQLITE_PERFORMANCE_TRACE
"PERFORMANCE_TRACE",
#endif

44
src/pcache1.c
View File

@@ -39,12 +39,13 @@
** size can vary according to architecture, compile-time options, and
** SQLite library version number.
**
** If SQLITE_PCACHE_SEPARATE_HEADER is defined, then the extension is obtained
** using a separate memory allocation from the database page content. This
** seeks to overcome the "clownshoe" problem (also called "internal
** fragmentation" in academic literature) of allocating a few bytes more
** than a power of two with the memory allocator rounding up to the next
** power of two, and leaving the rounded-up space unused.
** Historical note: It used to be that if the SQLITE_PCACHE_SEPARATE_HEADER
** was defined, then the page content would be held in a separate memory
** allocation from the PgHdr1. This was intended to avoid clownshoe memory
** allocations. However, the btree layer needs a small (16-byte) overrun
** area after the page content buffer. The header serves as that overrun
** area. Therefore SQLITE_PCACHE_SEPARATE_HEADER was discontinued to avoid
** any possibility of a memory error.
**
** This module tracks pointers to PgHdr1 objects. Only pcache.c communicates
** with this module. Information is passed back and forth as PgHdr1 pointers.
@@ -89,11 +90,16 @@ typedef struct PGroup PGroup;
/*
** Each cache entry is represented by an instance of the following
** structure. Unless SQLITE_PCACHE_SEPARATE_HEADER is defined, a buffer of
** PgHdr1.pCache->szPage bytes is allocated directly before this structure
** in memory.
** structure. A buffer of PgHdr1.pCache->szPage bytes is allocated
** directly before this structure and is used to cache the page content.
**
** Note: Variables isBulkLocal and isAnchor were once type "u8". That works,
** When reading a corrupt database file, it is possible that SQLite might
** read a few bytes (no more than 16 bytes) past the end of the page buffer.
** It will only read past the end of the page buffer, never write. This
** object is positioned immediately after the page buffer to serve as an
** overrun area, so that overreads are harmless.
**
** Variables isBulkLocal and isAnchor were once type "u8". That works,
** but causes a 2-byte gap in the structure for most architectures (since
** pointers must be either 4 or 8-byte aligned). As this structure is located
** in memory directly after the associated page data, if the database is
@@ -438,25 +444,13 @@ static PgHdr1 *pcache1AllocPage(PCache1 *pCache, int benignMalloc){
pcache1LeaveMutex(pCache->pGroup);
#endif
if( benignMalloc ){ sqlite3BeginBenignMalloc(); }
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
pPg = pcache1Alloc(pCache->szPage);
p = sqlite3Malloc(sizeof(PgHdr1) + pCache->szExtra);
if( !pPg || !p ){
pcache1Free(pPg);
sqlite3_free(p);
pPg = 0;
}
#else
pPg = pcache1Alloc(pCache->szAlloc);
#endif
if( benignMalloc ){ sqlite3EndBenignMalloc(); }
#ifdef SQLITE_ENABLE_MEMORY_MANAGEMENT
pcache1EnterMutex(pCache->pGroup);
#endif
if( pPg==0 ) return 0;
#ifndef SQLITE_PCACHE_SEPARATE_HEADER
p = (PgHdr1 *)&((u8 *)pPg)[pCache->szPage];
#endif
p->page.pBuf = pPg;
p->page.pExtra = &p[1];
p->isBulkLocal = 0;
@@ -480,9 +474,6 @@ static void pcache1FreePage(PgHdr1 *p){
pCache->pFree = p;
}else{
pcache1Free(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
sqlite3_free(p);
#endif
}
(*pCache->pnPurgeable)--;
}
@@ -1246,9 +1237,6 @@ int sqlite3PcacheReleaseMemory(int nReq){
&& p->isAnchor==0
){
nFree += pcache1MemSize(p->page.pBuf);
#ifdef SQLITE_PCACHE_SEPARATE_HEADER
nFree += sqlite3MemSize(p);
#endif
assert( PAGE_IS_UNPINNED(p) );
pcache1PinPage(p);
pcache1RemoveFromHash(p, 1);