diff options
Diffstat (limited to 'src/include/storage/bufpage.h')
| -rw-r--r-- | src/include/storage/bufpage.h | 27 |
1 files changed, 14 insertions, 13 deletions
diff --git a/src/include/storage/bufpage.h b/src/include/storage/bufpage.h index 8c887cab735..42f8f2fa496 100644 --- a/src/include/storage/bufpage.h +++ b/src/include/storage/bufpage.h @@ -103,7 +103,7 @@ typedef struct * space management information generic to any page * * pd_lsn - identifies xlog record for last change to this page. - * pd_tli - ditto. + * pd_checksum - page checksum, if set. * pd_flags - flag bits. * pd_lower - offset to start of free space. * pd_upper - offset to end of free space. @@ -114,9 +114,17 @@ typedef struct * The LSN is used by the buffer manager to enforce the basic rule of WAL: * "thou shalt write xlog before data". A dirty buffer cannot be dumped * to disk until xlog has been flushed at least as far as the page's LSN. - * We also store the 16 least significant bits of the TLI for identification - * purposes (it is not clear that this is actually necessary, but it seems - * like a good idea). + * + * pd_checksum stores the page checksum, if it has been set for this page; + * zero is a valid value for a checksum. If a checksum is not in use then + * we leave the field unset. This will typically mean the field is zero + * though non-zero values may also be present if databases have been + * pg_upgraded from releases prior to 9.3, when the same byte offset was + * used to store the current timelineid when the page was last updated. + * Note that there is no indication on a page as to whether the checksum + * is valid or not, a deliberate design choice which avoids the problem + * of relying on the page contents to decide whether to verify it. Hence + * there are no flag bits relating to checksums. * * pd_prune_xid is a hint field that helps determine whether pruning will be * useful. It is currently unused in index pages. @@ -138,10 +146,9 @@ typedef struct typedef struct PageHeaderData { /* XXX LSN is member of *any* block, not only page-organized ones */ - PageXLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog + PageXLogRecPtr pd_lsn; /* LSN: next byte after last byte of xlog * record for last change to this page */ - uint16 pd_tli; /* least significant bits of the TimeLineID - * containing the LSN */ + uint16 pd_checksum; /* checksum */ uint16 pd_flags; /* flag bits, see below */ LocationIndex pd_lower; /* offset to start of free space */ LocationIndex pd_upper; /* offset to end of free space */ @@ -335,12 +342,6 @@ typedef PageHeaderData *PageHeader; #define PageSetLSN(page, lsn) \ PageXLogRecPtrSet(((PageHeader) (page))->pd_lsn, lsn) -/* NOTE: only the 16 least significant bits are stored */ -#define PageGetTLI(page) \ - (((PageHeader) (page))->pd_tli) -#define PageSetTLI(page, tli) \ - (((PageHeader) (page))->pd_tli = (uint16) (tli)) - #define PageHasFreeLinePointers(page) \ (((PageHeader) (page))->pd_flags & PD_HAS_FREE_LINES) #define PageSetHasFreeLinePointers(page) \ |