diff options
Diffstat (limited to 'src/include/access/xlog_internal.h')
| -rw-r--r-- | src/include/access/xlog_internal.h | 33 |
1 files changed, 22 insertions, 11 deletions
diff --git a/src/include/access/xlog_internal.h b/src/include/access/xlog_internal.h index 75842328db4..a0b0b761ccb 100644 --- a/src/include/access/xlog_internal.h +++ b/src/include/access/xlog_internal.h @@ -11,7 +11,7 @@ * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.6 2004/12/31 22:03:21 pgsql Exp $ + * $PostgreSQL: pgsql/src/include/access/xlog_internal.h,v 1.7 2005/06/02 05:55:29 tgl Exp $ */ #ifndef XLOG_INTERNAL_H #define XLOG_INTERNAL_H @@ -25,15 +25,25 @@ /* * Header info for a backup block appended to an XLOG record. * - * Note that the backup block has its own CRC, and is not covered by - * the CRC of the XLOG record proper. Also note that we don't attempt - * to align either the BkpBlock struct or the block's data. + * As a trivial form of data compression, the XLOG code is aware that + * PG data pages usually contain an unused "hole" in the middle, which + * contains only zero bytes. If hole_length > 0 then we have removed + * such a "hole" from the stored data (and it's not counted in the + * XLOG record's CRC, either). Hence, the amount of block data actually + * present following the BkpBlock struct is BLCKSZ - hole_length bytes. + * + * Note that we don't attempt to align either the BkpBlock struct or the + * block's data. So, the struct must be copied to aligned local storage + * before use. */ typedef struct BkpBlock { - crc64 crc; - RelFileNode node; - BlockNumber block; + RelFileNode node; /* relation containing block */ + BlockNumber block; /* block number */ + uint16 hole_offset; /* number of bytes before "hole" */ + uint16 hole_length; /* number of bytes in "hole" */ + + /* ACTUAL BLOCK DATA FOLLOWS AT END OF STRUCT */ } BkpBlock; /* @@ -42,8 +52,9 @@ typedef struct BkpBlock * XLogRecord header will never be split across pages; if there's less than * SizeOfXLogRecord space left at the end of a page, we just waste it.) * - * Note that xl_rem_len includes backup-block data, unlike xl_len in the - * initial header. + * Note that xl_rem_len includes backup-block data; that is, it tracks + * xl_tot_len not xl_len in the initial header. Also note that the + * continuation data isn't necessarily aligned. */ typedef struct XLogContRecord { @@ -53,12 +64,12 @@ typedef struct XLogContRecord } XLogContRecord; -#define SizeOfXLogContRecord MAXALIGN(sizeof(XLogContRecord)) +#define SizeOfXLogContRecord sizeof(XLogContRecord) /* * Each page of XLOG file has a header like this: */ -#define XLOG_PAGE_MAGIC 0xD05C /* can be used as WAL version indicator */ +#define XLOG_PAGE_MAGIC 0xD05D /* can be used as WAL version indicator */ typedef struct XLogPageHeaderData { |