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In the pager, load the content of pages which were initialized with

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noContent==1 if they are subsequently requested with noContent==0. (CVS 3875)

FossilOrigin-Name: d0745a43b6e037d16e1ec38c7c4d961a80d1ef48
This commit is contained in:
drh
2007-04-26 12:11:28 +00:00
parent 7a521cfb79
commit d33d5a8978
3 changed files with 43 additions and 21 deletions
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50
src/pager.c
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@@ -18,7 +18,7 @@
** file simultaneously, or one process from reading the database while
** another is writing.
**
** @(#) $Id: pager.c,v 1.329 2007/04/16 15:02:19 drh Exp $
** @(#) $Id: pager.c,v 1.330 2007/04/26 12:11:28 drh Exp $
*/
#ifndef SQLITE_OMIT_DISKIO
#include "sqliteInt.h"
@@ -2922,13 +2922,32 @@ pager_allocate_out:
return rc;
}
/*
** Make sure we have the content for a page. If the page was
** previously acquired with noContent==1, then the content was
** just initialized to zeros instead of being read from disk.
** But now we need the real data off of disk. So make sure we
** have it. Read it in if we do not have it already.
*/
static int pager_get_content(PgHdr *pPg){
if( pPg->needRead ){
int rc = readDbPage(pPg->pPager, pPg, pPg->pgno);
if( rc==SQLITE_OK ){
pPg->needRead = 0;
}else{
return rc;
}
}
return SQLITE_OK;
}
/*
** Acquire a page.
**
** A read lock on the disk file is obtained when the first page is acquired.
** This read lock is dropped when the last page is released.
**
** A _get works for any page number greater than 0. If the database
** This routine works for any page number greater than 0. If the database
** file is smaller than the requested page, then no actual disk
** read occurs and the memory image of the page is initialized to
** all zeros. The extra data appended to a page is always initialized
@@ -2937,12 +2956,12 @@ pager_allocate_out:
** The acquisition might fail for several reasons. In all cases,
** an appropriate error code is returned and *ppPage is set to NULL.
**
** See also sqlite3PagerLookup(). Both this routine and _lookup() attempt
** See also sqlite3PagerLookup(). Both this routine and Lookup() attempt
** to find a page in the in-memory cache first. If the page is not already
** in memory, this routine goes to disk to read it in whereas _lookup()
** in memory, this routine goes to disk to read it in whereas Lookup()
** just returns 0. This routine acquires a read-lock the first time it
** has to go to disk, and could also playback an old journal if necessary.
** Since _lookup() never goes to disk, it never has to deal with locks
** Since Lookup() never goes to disk, it never has to deal with locks
** or journal files.
**
** If noContent is false, the page contents are actually read from disk.
@@ -2950,8 +2969,9 @@ pager_allocate_out:
** of the page at this time, so do not do a disk read. Just fill in the
** page content with zeros. But mark the fact that we have not read the
** content by setting the PgHdr.needRead flag. Later on, if
** sqlite3PagerWrite() is called on this page, that means that the
** content is needed and the disk read should occur at that point.
** sqlite3PagerWrite() is called on this page or if this routine is
** called again with noContent==0, that means that the content is needed
** and the disk read should occur at that point.
*/
int sqlite3PagerAcquire(
Pager *pPager, /* The pager open on the database file */
@@ -3060,6 +3080,12 @@ int sqlite3PagerAcquire(
/* The requested page is in the page cache. */
assert(pPager->nRef>0 || pgno==1);
PAGER_INCR(pPager->nHit);
if( !noContent ){
rc = pager_get_content(pPg);
if( rc ){
return rc;
}
}
page_ref(pPg);
}
*ppPage = pPg;
@@ -3367,13 +3393,9 @@ static int pager_write(PgHdr *pPg){
** can be stored in the rollback journal. So do the read at this
** time.
*/
if( pPg->needRead ){
rc = readDbPage(pPager, pPg, pPg->pgno);
if( rc==SQLITE_OK ){
pPg->needRead = 0;
}else{
return rc;
}
rc = pager_get_content(pPg);
if( rc ){
return rc;
}
/* Mark the page as dirty. If the page has already been written