@ -1230,11 +1230,6 @@ SimpleLruTruncate(SlruCtl ctl, int cutoffPage)
/* update the stats counter of truncates */
pgstat_count_slru_truncate ( shared - > slru_stats_idx ) ;
/*
* The cutoff point is the start of the segment containing cutoffPage .
*/
cutoffPage - = cutoffPage % SLRU_PAGES_PER_SEGMENT ;
/*
* Scan shared memory and remove any pages preceding the cutoff page , to
* ensure we won ' t rewrite them later . ( Since this is normally called in
@ -1247,9 +1242,7 @@ restart:;
/*
* While we are holding the lock , make an important safety check : the
* planned cutoff point must be < = the current endpoint page . Otherwise we
* have already wrapped around , and proceeding with the truncation would
* risk removing the current segment .
* current endpoint page must not be eligible for removal .
*/
if ( ctl - > PagePrecedes ( shared - > latest_page_number , cutoffPage ) )
{
@ -1281,8 +1274,11 @@ restart:;
* Hmm , we have ( or may have ) I / O operations acting on the page , so
* we ' ve got to wait for them to finish and then start again . This is
* the same logic as in SlruSelectLRUPage . ( XXX if page is dirty ,
* wouldn ' t it be OK to just discard it without writing it ? For now ,
* keep the logic the same as it was . )
* wouldn ' t it be OK to just discard it without writing it ?
* SlruMayDeleteSegment ( ) uses a stricter qualification , so we might
* not delete this page in the end ; even if we don ' t delete it , we
* won ' t have cause to read its data again . For now , keep the logic
* the same as it was . )
*/
if ( shared - > page_status [ slotno ] = = SLRU_PAGE_VALID )
SlruInternalWritePage ( ctl , slotno , NULL ) ;
@ -1377,19 +1373,134 @@ restart:
LWLockRelease ( shared - > ControlLock ) ;
}
/*
* Determine whether a segment is okay to delete .
*
* segpage is the first page of the segment , and cutoffPage is the oldest ( in
* PagePrecedes order ) page in the SLRU containing still - useful data . Since
* every core PagePrecedes callback implements " wrap around " , check the
* segment ' s first and last pages :
*
* first < cutoff & & last < cutoff : yes
* first < cutoff & & last > = cutoff : no ; cutoff falls inside this segment
* first > = cutoff & & last < cutoff : no ; wrap point falls inside this segment
* first > = cutoff & & last > = cutoff : no ; every page of this segment is too young
*/
static bool
SlruMayDeleteSegment ( SlruCtl ctl , int segpage , int cutoffPage )
{
int seg_last_page = segpage + SLRU_PAGES_PER_SEGMENT - 1 ;
Assert ( segpage % SLRU_PAGES_PER_SEGMENT = = 0 ) ;
return ( ctl - > PagePrecedes ( segpage , cutoffPage ) & &
ctl - > PagePrecedes ( seg_last_page , cutoffPage ) ) ;
}
# ifdef USE_ASSERT_CHECKING
static void
SlruPagePrecedesTestOffset ( SlruCtl ctl , int per_page , uint32 offset )
{
TransactionId lhs ,
rhs ;
int newestPage ,
oldestPage ;
TransactionId newestXact ,
oldestXact ;
/*
* Compare an XID pair having undefined order ( see RFC 1982 ) , a pair at
* " opposite ends " of the XID space . TransactionIdPrecedes ( ) treats each
* as preceding the other . If RHS is oldestXact , LHS is the first XID we
* must not assign .
*/
lhs = per_page + offset ; /* skip first page to avoid non-normal XIDs */
rhs = lhs + ( 1U < < 31 ) ;
Assert ( TransactionIdPrecedes ( lhs , rhs ) ) ;
Assert ( TransactionIdPrecedes ( rhs , lhs ) ) ;
Assert ( ! TransactionIdPrecedes ( lhs - 1 , rhs ) ) ;
Assert ( TransactionIdPrecedes ( rhs , lhs - 1 ) ) ;
Assert ( TransactionIdPrecedes ( lhs + 1 , rhs ) ) ;
Assert ( ! TransactionIdPrecedes ( rhs , lhs + 1 ) ) ;
Assert ( ! TransactionIdFollowsOrEquals ( lhs , rhs ) ) ;
Assert ( ! TransactionIdFollowsOrEquals ( rhs , lhs ) ) ;
Assert ( ! ctl - > PagePrecedes ( lhs / per_page , lhs / per_page ) ) ;
Assert ( ! ctl - > PagePrecedes ( lhs / per_page , rhs / per_page ) ) ;
Assert ( ! ctl - > PagePrecedes ( rhs / per_page , lhs / per_page ) ) ;
Assert ( ! ctl - > PagePrecedes ( ( lhs - per_page ) / per_page , rhs / per_page ) ) ;
Assert ( ctl - > PagePrecedes ( rhs / per_page , ( lhs - 3 * per_page ) / per_page ) ) ;
Assert ( ctl - > PagePrecedes ( rhs / per_page , ( lhs - 2 * per_page ) / per_page ) ) ;
Assert ( ctl - > PagePrecedes ( rhs / per_page , ( lhs - 1 * per_page ) / per_page )
| | ( 1U < < 31 ) % per_page ! = 0 ) ; /* See CommitTsPagePrecedes() */
Assert ( ctl - > PagePrecedes ( ( lhs + 1 * per_page ) / per_page , rhs / per_page )
| | ( 1U < < 31 ) % per_page ! = 0 ) ;
Assert ( ctl - > PagePrecedes ( ( lhs + 2 * per_page ) / per_page , rhs / per_page ) ) ;
Assert ( ctl - > PagePrecedes ( ( lhs + 3 * per_page ) / per_page , rhs / per_page ) ) ;
Assert ( ! ctl - > PagePrecedes ( rhs / per_page , ( lhs + per_page ) / per_page ) ) ;
/*
* GetNewTransactionId ( ) has assigned the last XID it can safely use , and
* that XID is in the * LAST * page of the second segment . We must not
* delete that segment .
*/
newestPage = 2 * SLRU_PAGES_PER_SEGMENT - 1 ;
newestXact = newestPage * per_page + offset ;
Assert ( newestXact / per_page = = newestPage ) ;
oldestXact = newestXact + 1 ;
oldestXact - = 1U < < 31 ;
oldestPage = oldestXact / per_page ;
Assert ( ! SlruMayDeleteSegment ( ctl ,
( newestPage -
newestPage % SLRU_PAGES_PER_SEGMENT ) ,
oldestPage ) ) ;
/*
* GetNewTransactionId ( ) has assigned the last XID it can safely use , and
* that XID is in the * FIRST * page of the second segment . We must not
* delete that segment .
*/
newestPage = SLRU_PAGES_PER_SEGMENT ;
newestXact = newestPage * per_page + offset ;
Assert ( newestXact / per_page = = newestPage ) ;
oldestXact = newestXact + 1 ;
oldestXact - = 1U < < 31 ;
oldestPage = oldestXact / per_page ;
Assert ( ! SlruMayDeleteSegment ( ctl ,
( newestPage -
newestPage % SLRU_PAGES_PER_SEGMENT ) ,
oldestPage ) ) ;
}
/*
* Unit - test a PagePrecedes function .
*
* This assumes every uint32 > = FirstNormalTransactionId is a valid key . It
* assumes each value occupies a contiguous , fixed - size region of SLRU bytes .
* ( MultiXactMemberCtl separates flags from XIDs . AsyncCtl has
* variable - length entries , no keys , and no random access . These unit tests
* do not apply to them . )
*/
void
SlruPagePrecedesUnitTests ( SlruCtl ctl , int per_page )
{
/* Test first, middle and last entries of a page. */
SlruPagePrecedesTestOffset ( ctl , per_page , 0 ) ;
SlruPagePrecedesTestOffset ( ctl , per_page , per_page / 2 ) ;
SlruPagePrecedesTestOffset ( ctl , per_page , per_page - 1 ) ;
}
# endif
/*
* SlruScanDirectory callback
* This callback reports true if there ' s any segment prior to the one
* containing the page passed as " data " .
* This callback reports true if there ' s any segment wholly prior to the
* one containing the page passed as " data " .
*/
bool
SlruScanDirCbReportPresence ( SlruCtl ctl , char * filename , int segpage , void * data )
{
int cutoffPage = * ( int * ) data ;
cutoffPage - = cutoffPage % SLRU_PAGES_PER_SEGMENT ;
if ( ctl - > PagePrecedes ( segpage , cutoffPage ) )
if ( SlruMayDeleteSegment ( ctl , segpage , cutoffPage ) )
return true ; /* found one; don't iterate any more */
return false ; /* keep going */
@ -1404,7 +1515,7 @@ SlruScanDirCbDeleteCutoff(SlruCtl ctl, char *filename, int segpage, void *data)
{
int cutoffPage = * ( int * ) data ;
if ( ctl - > PagePrecedes ( segpage , cutoffPage ) )
if ( SlruMayDeleteSegment ( ctl , segpage , cutoffPage ) )
SlruInternalDeleteSegment ( ctl , segpage / SLRU_PAGES_PER_SEGMENT ) ;
return false ; /* keep going */
Noah Misch
5 years ago