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Memory-mapped I/O is now on by default. The "PRAGMA mmap_limit(N)" can be

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used to issue a hint to the VFS to limit mmap space to N bytes.  The VFS
is free to ignore that hint if desired.  However, if "PRAGMA mmap_limit(0)"
is used, xFetch is never called.

FossilOrigin-Name: 1b37c4effdd03aa2ea938a71b4f22ed27391689b
This commit is contained in:
drh
2013-03-25 23:09:28 +00:00
parent d1ab8065c1
commit 0d0614bdc6
18 changed files with 84 additions and 92 deletions
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25
src/pragma.c
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@@ -745,26 +745,23 @@ void sqlite3Pragma(
}else
/*
** PRAGMA [database.]mmap_size
** PRAGMA [database.]mmap_size=N
** PRAGMA [database.]mmap_limit(N)
**
** Used to set or query the mapping size limit. The mapping size limit is
** Used to set mapping size limit. The mapping size limit is
** used to limit the aggregate size of all memory mapped regions of the
** database file. If this parameter is set to zero, then memory mapping
** is not used at all. If it is set to a positive value, then it is
** interpreted as a maximum size in pages. If set to less than zero, then
** the absolute value is interpreted as a size limit in KB.
** is not used at all. The parameter N is measured in bytes.
**
** The default value is zero (do not use memory mapped IO).
** This value is advisory. The underlying VFS is free to memory map
** as little or as much as it wants. Except, if N is set to 0 then the
** upper layers will never invoke the xFetch interfaces to the VFS.
*/
if( sqlite3StrICmp(zLeft,"mmap_size")==0 ){
if( sqlite3StrICmp(zLeft,"mmap_limit")==0 ){
assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
if( !zRight ){
returnSingleInt(pParse, "mmap_size", pDb->pSchema->mmap_size);
}else{
int size = sqlite3Atoi(zRight);
pDb->pSchema->mmap_size = size;
sqlite3BtreeSetMmapSize(pDb->pBt, pDb->pSchema->mmap_size);
if( zRight ){
sqlite3_int64 size;
sqlite3Atoi64(zRight, &size, 1000, SQLITE_UTF8);
sqlite3BtreeSetMmapLimit(pDb->pBt, size);
}
}else