diff options
Diffstat (limited to 'src/include/access/slru.h')
| -rw-r--r-- | src/include/access/slru.h | 27 |
1 files changed, 23 insertions, 4 deletions
diff --git a/src/include/access/slru.h b/src/include/access/slru.h index 8e820ae72dd..4cc40ba5f70 100644 --- a/src/include/access/slru.h +++ b/src/include/access/slru.h @@ -6,7 +6,7 @@ * Portions Copyright (c) 1996-2010, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/include/access/slru.h,v 1.25 2010/01/02 16:58:00 momjian Exp $ + * $PostgreSQL: pgsql/src/include/access/slru.h,v 1.26 2010/02/16 22:34:50 tgl Exp $ * *------------------------------------------------------------------------- */ @@ -18,6 +18,25 @@ /* + * Define SLRU segment size. A page is the same BLCKSZ as is used everywhere + * else in Postgres. The segment size can be chosen somewhat arbitrarily; + * we make it 32 pages by default, or 256Kb, i.e. 1M transactions for CLOG + * or 64K transactions for SUBTRANS. + * + * Note: because TransactionIds are 32 bits and wrap around at 0xFFFFFFFF, + * page numbering also wraps around at 0xFFFFFFFF/xxxx_XACTS_PER_PAGE (where + * xxxx is CLOG or SUBTRANS, respectively), and segment numbering at + * 0xFFFFFFFF/xxxx_XACTS_PER_PAGE/SLRU_PAGES_PER_SEGMENT. We need + * take no explicit notice of that fact in slru.c, except when comparing + * segment and page numbers in SimpleLruTruncate (see PagePrecedes()). + * + * Note: slru.c currently assumes that segment file names will be four hex + * digits. This sets a lower bound on the segment size (64K transactions + * for 32-bit TransactionIds). + */ +#define SLRU_PAGES_PER_SEGMENT 32 + +/* * Page status codes. Note that these do not include the "dirty" bit. * page_dirty can be TRUE only in the VALID or WRITE_IN_PROGRESS states; * in the latter case it implies that the page has been re-dirtied since @@ -55,8 +74,8 @@ typedef struct SlruSharedData /* * Optional array of WAL flush LSNs associated with entries in the SLRU * pages. If not zero/NULL, we must flush WAL before writing pages (true - * for pg_clog, false for multixact and pg_subtrans). group_lsn[] has - * lsn_groups_per_page entries per buffer slot, each containing the + * for pg_clog, false for multixact, pg_subtrans, pg_notify). group_lsn[] + * has lsn_groups_per_page entries per buffer slot, each containing the * highest LSN known for a contiguous group of SLRU entries on that slot's * page. */ @@ -94,7 +113,7 @@ typedef struct SlruCtlData /* * This flag tells whether to fsync writes (true for pg_clog and multixact - * stuff, false for pg_subtrans). + * stuff, false for pg_subtrans and pg_notify). */ bool do_fsync; |