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