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Add extension "mmapwarm.c". Provides function sqlite3_mmap_warm(), used to

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"warm up" the memory mapping used by SQLite in mmap mode to access db file
content.

FossilOrigin-Name: d4a30b91f9aad93510baead8c04ee51b82c98763be5a224ed4873298214c963a
This commit is contained in:
dan
2017-09-18 16:28:56 +00:00
parent 2acd24d90c
commit 460f1fa55c
7 changed files with 158 additions and 13 deletions
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108
ext/misc/mmapwarm.c Normal file
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/*
** 2017-09-18
**
** The author disclaims copyright to this source code. In place of
** a legal notice, here is a blessing:
**
** May you do good and not evil.
** May you find forgiveness for yourself and forgive others.
** May you share freely, never taking more than you give.
**
*************************************************************************
**
*/
#include "sqlite3.h"
/*
** This function is used to touch each page of a mapping of a memory
** mapped SQLite database. Assuming that the system has sufficient free
** memory and supports sufficiently large mappings, this causes the OS
** to cache the entire database in main memory, making subsequent
** database accesses faster.
**
** If the second parameter to this function is not NULL, it is the name of
** the specific database to operate on (i.e. "main" or the name of an
** attached database).
**
** SQLITE_OK is returned if successful, or an SQLite error code otherwise.
** It is not considered an error if the file is not memory-mapped, or if
** the mapping does not span the entire file. If an error does occur, a
** transaction may be left open on the database file.
**
** It is illegal to call this function when the database handle has an
** open transaction. SQLITE_MISUSE is returned in this case.
*/
int sqlite3_mmap_warm(sqlite3 *db, const char *zDb){
int rc = SQLITE_OK;
char *zSql = 0;
int pgsz = 0;
int nTotal = 0;
if( 0==sqlite3_get_autocommit(db) ) return SQLITE_MISUSE;
/* Open a read-only transaction on the file in question */
zSql = sqlite3_mprintf("BEGIN; SELECT * FROM %s%q%ssqlite_master",
(zDb ? "'" : ""), (zDb ? zDb : ""), (zDb ? "'." : "")
);
if( zSql==0 ) return SQLITE_NOMEM;
rc = sqlite3_exec(db, zSql, 0, 0, 0);
sqlite3_free(zSql);
/* Find the SQLite page size of the file */
if( rc==SQLITE_OK ){
zSql = sqlite3_mprintf("PRAGMA %s%q%spage_size",
(zDb ? "'" : ""), (zDb ? zDb : ""), (zDb ? "'." : "")
);
if( zSql==0 ){
rc = SQLITE_NOMEM;
}else{
sqlite3_stmt *pPgsz = 0;
rc = sqlite3_prepare_v2(db, zSql, -1, &pPgsz, 0);
sqlite3_free(zSql);
if( rc==SQLITE_OK ){
if( sqlite3_step(pPgsz)==SQLITE_ROW ){
pgsz = sqlite3_column_int(pPgsz, 0);
}
rc = sqlite3_finalize(pPgsz);
}
if( rc==SQLITE_OK && pgsz==0 ){
rc = SQLITE_ERROR;
}
}
}
/* Touch each mmap'd page of the file */
if( rc==SQLITE_OK ){
int rc2;
sqlite3_file *pFd = 0;
rc = sqlite3_file_control(db, zDb, SQLITE_FCNTL_FILE_POINTER, &pFd);
if( rc==SQLITE_OK && pFd->pMethods->iVersion>=3 ){
sqlite3_int64 iPg = 1;
sqlite3_io_methods const *p = pFd->pMethods;
while( 1 ){
unsigned char *pMap;
rc = p->xFetch(pFd, pgsz*iPg, pgsz, (void**)&pMap);
if( rc!=SQLITE_OK || pMap==0 ) break;
nTotal += pMap[0];
nTotal += pMap[pgsz-1];
rc = p->xUnfetch(pFd, pgsz*iPg, (void*)pMap);
if( rc!=SQLITE_OK ) break;
iPg++;
}
sqlite3_log(SQLITE_OK,
"sqlite3_mmap_warm_cache: Warmed up %d pages of %s", iPg==1?0:iPg,
sqlite3_db_filename(db, zDb)
);
}
rc2 = sqlite3_exec(db, "END", 0, 0, 0);
if( rc==SQLITE_OK ) rc = rc2;
}
return rc;
}