diff options
Diffstat (limited to 'src/include/access/slru.h')
| -rw-r--r-- | src/include/access/slru.h | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/src/include/access/slru.h b/src/include/access/slru.h index 34964675d20..dd52e8cec7e 100644 --- a/src/include/access/slru.h +++ b/src/include/access/slru.h @@ -118,9 +118,14 @@ typedef struct SlruCtlData SyncRequestHandler sync_handler; /* - * Decide which of two page numbers is "older" for truncation purposes. We - * need to use comparison of TransactionIds here in order to do the right - * thing with wraparound XID arithmetic. + * Decide whether a page is "older" for truncation and as a hint for + * evicting pages in LRU order. Return true if every entry of the first + * argument is older than every entry of the second argument. Note that + * !PagePrecedes(a,b) && !PagePrecedes(b,a) need not imply a==b; it also + * arises when some entries are older and some are not. For SLRUs using + * SimpleLruTruncate(), this must use modular arithmetic. (For others, + * the behavior of this callback has no functional implications.) Use + * SlruPagePrecedesUnitTests() in SLRUs meeting its criteria. */ bool (*PagePrecedes) (int, int); @@ -145,6 +150,11 @@ extern int SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno, TransactionId xid); extern void SimpleLruWritePage(SlruCtl ctl, int slotno); extern void SimpleLruWriteAll(SlruCtl ctl, bool allow_redirtied); +#ifdef USE_ASSERT_CHECKING +extern void SlruPagePrecedesUnitTests(SlruCtl ctl, int per_page); +#else +#define SlruPagePrecedesUnitTests(ctl, per_page) do {} while (0) +#endif extern void SimpleLruTruncate(SlruCtl ctl, int cutoffPage); extern bool SimpleLruDoesPhysicalPageExist(SlruCtl ctl, int pageno); |