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Change the Pager.hasBeenUsed flag into Pager.hasHeldSharedLock in order to

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take it off the critical path in sqlite3PagerAcquire().

FossilOrigin-Name: b79096be7cb02aae2f303db33a8bf19e69204374
This commit is contained in:
drh
2015-09-03 17:54:32 +00:00
parent 076e85f59c
commit c98a4cc8b6
3 changed files with 13 additions and 12 deletions
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11
src/pager.c
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@@ -647,7 +647,7 @@ struct Pager {
u8 doNotSpill; /* Do not spill the cache when non-zero */
u8 subjInMemory; /* True to use in-memory sub-journals */
u8 bUseFetch; /* True to use xFetch() */
u8 hasBeenUsed; /* True if any content previously read */
u8 hasHeldSharedLock; /* True if a shared lock has ever been held */
Pgno dbSize; /* Number of pages in the database */
Pgno dbOrigSize; /* dbSize before the current transaction */
Pgno dbFileSize; /* Number of pages in the database file */
@@ -5097,10 +5097,10 @@ int sqlite3PagerSharedLock(Pager *pPager){
);
}
if( !pPager->tempFile && pPager->hasBeenUsed ){
if( !pPager->tempFile && pPager->hasHeldSharedLock ){
/* The shared-lock has just been acquired then check to
** see if the database has been modified. If the database has changed,
** flush the cache. The pPager->hasBeenUsed flag prevents this from
** flush the cache. The hasHeldSharedLock flag prevents this from
** occurring on the very first access to a file, in order to save a
** single unnecessary sqlite3OsRead() call at the start-up.
**
@@ -5170,6 +5170,7 @@ int sqlite3PagerSharedLock(Pager *pPager){
assert( pPager->eState==PAGER_OPEN );
}else{
pPager->eState = PAGER_READER;
pPager->hasHeldSharedLock = 1;
}
return rc;
}
@@ -5267,7 +5268,7 @@ int sqlite3PagerAcquire(
if( pgno==0 ){
return SQLITE_CORRUPT_BKPT;
}
pPager->hasBeenUsed = 1;
assert( pPager->hasHeldSharedLock==1 );
/* If the pager is in the error state, return an error immediately.
** Otherwise, request the page from the PCache layer. */
@@ -5422,7 +5423,7 @@ DbPage *sqlite3PagerLookup(Pager *pPager, Pgno pgno){
assert( pgno!=0 );
assert( pPager->pPCache!=0 );
pPage = sqlite3PcacheFetch(pPager->pPCache, pgno, 0);
assert( pPage==0 || pPager->hasBeenUsed );
assert( pPage==0 || pPager->hasHeldSharedLock );
if( pPage==0 ) return 0;
return sqlite3PcacheFetchFinish(pPager->pPCache, pgno, pPage);
}