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Refactoring the mmap interface. The controlling pragma is now "mmap_size"

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instead of "mmap_limit".  Also change SQLITE_CONFIG_MMAP_LIMIT and
SQLITE_FCNTL_MMAP_LIMIT to SQLITE_CONFIG_MMAP_SIZE and
SQLITE_FCNTL_MMAP_SIZE, respecctively.  
The default mmap_size is now always 0, meaning that
memory mapped I/O is off by default.  There is a new compile-time option
SQLITE_MAX_MMAP_SIZE that determines a hard upper bound on the mmap_size.
Setting SQLITE_MAX_MMAP_SIZE to zero disables the memory-mapped I/O logic
and causes it to be omitted from the build.  An extra argument is added
to SQLITE_CONFIG_MMAP_SIZE that can optionally lower the SQLITE_MAX_MMAP_SIZE
at start-time. The SQLITE_MAX_MMAP_SIZE is zero for platforms where we 
know that it does not work, meaning that it cannot be turned on by mistake
on those platforms.

FossilOrigin-Name: ea1404a10abd7f68e1f8e0708c8a3199d1f79665
This commit is contained in:
drh
2013-04-15 17:03:42 +00:00
parent a1710cc2ea
commit 9b4c59fa1b
31 changed files with 245 additions and 213 deletions
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26
src/pragma.c
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@@ -746,39 +746,39 @@ void sqlite3Pragma(
}else
/*
** PRAGMA [database.]mmap_limit(N)
** PRAGMA [database.]mmap_size(N)
**
** 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 N is negative, then the default memory map
** limit determined by sqlite3_config(SQLITE_CONFIG_MMAP_LIMIT) is set.
** limit determined by sqlite3_config(SQLITE_CONFIG_MMAP_SIZE) is set.
** The parameter N is measured in bytes.
**
** 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_limit")==0 ){
sqlite3_int64 mx;
if( sqlite3StrICmp(zLeft,"mmap_size")==0 ){
sqlite3_int64 sz;
assert( sqlite3SchemaMutexHeld(db, iDb, 0) );
if( zRight ){
int ii;
sqlite3Atoi64(zRight, &mx, 1000, SQLITE_UTF8);
if( mx<0 ) mx = sqlite3GlobalConfig.mxMmap;
if( pId2->n==0 ) db->mxMmap = mx;
sqlite3Atoi64(zRight, &sz, 1000, SQLITE_UTF8);
if( sz<0 ) sz = sqlite3GlobalConfig.szMmap;
if( pId2->n==0 ) db->szMmap = sz;
for(ii=db->nDb-1; ii>=0; ii--){
if( db->aDb[ii].pBt && (ii==iDb || pId2->n==0) ){
sqlite3BtreeSetMmapLimit(db->aDb[ii].pBt, mx);
sqlite3BtreeSetMmapLimit(db->aDb[ii].pBt, sz);
}
}
}
mx = -1;
if( sqlite3_file_control(db,zDb,SQLITE_FCNTL_MMAP_LIMIT,&mx)==SQLITE_OK ){
#if defined(SQLITE_DISABLE_MMAP)
mx = 0;
sz = -1;
if( sqlite3_file_control(db,zDb,SQLITE_FCNTL_MMAP_SIZE,&sz)==SQLITE_OK ){
#if SQLITE_MAX_MMAP_SIZE==0
sz = 0;
#endif
returnSingleInt(pParse, "mmap_limit", mx);
returnSingleInt(pParse, "mmap_size", sz);
}
}else