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Allow writers to write dirty pages to the log mid-transaction in order to free memory.

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FossilOrigin-Name: ecd828f96909895535d7dc744e5a8530e234e04d
This commit is contained in:
dan
2010-04-15 16:45:34 +00:00
parent bb2e9c97fc
commit 4cc6fb6165
4 changed files with 170 additions and 76 deletions
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140
src/pager.c
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@@ -3253,76 +3253,80 @@ static int pagerStress(void *p, PgHdr *pPg){
assert( pPg->pPager==pPager );
assert( pPg->flags&PGHDR_DIRTY );
if( pagerUseLog(pPager) ) return SQLITE_OK;
/* The doNotSync flag is set by the sqlite3PagerWrite() function while it
** is journalling a set of two or more database pages that are stored
** on the same disk sector. Syncing the journal is not allowed while
** this is happening as it is important that all members of such a
** set of pages are synced to disk together. So, if the page this function
** is trying to make clean will require a journal sync and the doNotSync
** flag is set, return without doing anything. The pcache layer will
** just have to go ahead and allocate a new page buffer instead of
** reusing pPg.
**
** Similarly, if the pager has already entered the error state, do not
** try to write the contents of pPg to disk.
*/
if( NEVER(pPager->errCode)
|| (pPager->doNotSync && pPg->flags&PGHDR_NEED_SYNC)
){
return SQLITE_OK;
}
/* Sync the journal file if required. */
if( pPg->flags&PGHDR_NEED_SYNC ){
rc = syncJournal(pPager);
if( rc==SQLITE_OK && pPager->fullSync &&
!(pPager->journalMode==PAGER_JOURNALMODE_MEMORY) &&
!(sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND)
if( pagerUseLog(pPager) ){
/* Write a single frame for this page to the log. */
assert( pPg->pDirty==0 );
rc = sqlite3LogFrames(pPager->pLog, pPager->pageSize, pPg, 0, 0, 0);
}else{
/* The doNotSync flag is set by the sqlite3PagerWrite() function while it
** is journalling a set of two or more database pages that are stored
** on the same disk sector. Syncing the journal is not allowed while
** this is happening as it is important that all members of such a
** set of pages are synced to disk together. So, if the page this function
** is trying to make clean will require a journal sync and the doNotSync
** flag is set, return without doing anything. The pcache layer will
** just have to go ahead and allocate a new page buffer instead of
** reusing pPg.
**
** Similarly, if the pager has already entered the error state, do not
** try to write the contents of pPg to disk.
*/
if( NEVER(pPager->errCode)
|| (pPager->doNotSync && pPg->flags&PGHDR_NEED_SYNC)
){
pPager->nRec = 0;
rc = writeJournalHdr(pPager);
return SQLITE_OK;
}
/* Sync the journal file if required. */
if( pPg->flags&PGHDR_NEED_SYNC ){
rc = syncJournal(pPager);
if( rc==SQLITE_OK && pPager->fullSync &&
!(pPager->journalMode==PAGER_JOURNALMODE_MEMORY) &&
!(sqlite3OsDeviceCharacteristics(pPager->fd)&SQLITE_IOCAP_SAFE_APPEND)
){
pPager->nRec = 0;
rc = writeJournalHdr(pPager);
}
}
/* If the page number of this page is larger than the current size of
** the database image, it may need to be written to the sub-journal.
** This is because the call to pager_write_pagelist() below will not
** actually write data to the file in this case.
**
** Consider the following sequence of events:
**
** BEGIN;
** <journal page X>
** <modify page X>
** SAVEPOINT sp;
** <shrink database file to Y pages>
** pagerStress(page X)
** ROLLBACK TO sp;
**
** If (X>Y), then when pagerStress is called page X will not be written
** out to the database file, but will be dropped from the cache. Then,
** following the "ROLLBACK TO sp" statement, reading page X will read
** data from the database file. This will be the copy of page X as it
** was when the transaction started, not as it was when "SAVEPOINT sp"
** was executed.
**
** The solution is to write the current data for page X into the
** sub-journal file now (if it is not already there), so that it will
** be restored to its current value when the "ROLLBACK TO sp" is
** executed.
*/
if( NEVER(
rc==SQLITE_OK && pPg->pgno>pPager->dbSize && subjRequiresPage(pPg)
) ){
rc = subjournalPage(pPg);
}
/* Write the contents of the page out to the database file. */
if( rc==SQLITE_OK ){
pPg->pDirty = 0;
rc = pager_write_pagelist(pPg);
}
}
/* If the page number of this page is larger than the current size of
** the database image, it may need to be written to the sub-journal.
** This is because the call to pager_write_pagelist() below will not
** actually write data to the file in this case.
**
** Consider the following sequence of events:
**
** BEGIN;
** <journal page X>
** <modify page X>
** SAVEPOINT sp;
** <shrink database file to Y pages>
** pagerStress(page X)
** ROLLBACK TO sp;
**
** If (X>Y), then when pagerStress is called page X will not be written
** out to the database file, but will be dropped from the cache. Then,
** following the "ROLLBACK TO sp" statement, reading page X will read
** data from the database file. This will be the copy of page X as it
** was when the transaction started, not as it was when "SAVEPOINT sp"
** was executed.
**
** The solution is to write the current data for page X into the
** sub-journal file now (if it is not already there), so that it will
** be restored to its current value when the "ROLLBACK TO sp" is
** executed.
*/
if( NEVER(
rc==SQLITE_OK && pPg->pgno>pPager->dbSize && subjRequiresPage(pPg)
) ){
rc = subjournalPage(pPg);
}
/* Write the contents of the page out to the database file. */
if( rc==SQLITE_OK ){
pPg->pDirty = 0;
rc = pager_write_pagelist(pPg);
}
/* Mark the page as clean. */