diff options
Diffstat (limited to 'src/include/access/xlog.h')
| -rw-r--r-- | src/include/access/xlog.h | 40 |
1 files changed, 29 insertions, 11 deletions
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h index 554c3c3aec7..7547d7f5b9f 100644 --- a/src/include/access/xlog.h +++ b/src/include/access/xlog.h @@ -6,7 +6,7 @@ * 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.h,v 1.63 2005/06/06 17:01:24 tgl Exp $ + * $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.64 2005/06/06 20:22:58 tgl Exp $ */ #ifndef XLOG_H #define XLOG_H @@ -91,24 +91,42 @@ typedef struct XLogRecord extern int sync_method; /* - * List of these structs is used to pass data to XLogInsert(). + * The rmgr data to be written by XLogInsert() is defined by a chain of + * one or more XLogRecData structs. (Multiple structs would be used when + * parts of the source data aren't physically adjacent in memory, or when + * multiple associated buffers need to be specified.) * * If buffer is valid then XLOG will check if buffer must be backed up * (ie, whether this is first change of that page since last checkpoint). * If so, the whole page contents are attached to the XLOG record, and XLOG * sets XLR_BKP_BLOCK_X bit in xl_info. Note that the buffer must be pinned - * and locked while this is going on, so that it won't change under us. - * NB: when this happens, we do not bother to insert the associated data into - * the XLOG record, since we assume it's present in the buffer. Therefore, - * rmgr redo routines MUST pay attention to XLR_BKP_BLOCK_X to know what - * is actually stored in the XLOG record. + * and exclusive-locked by the caller, so that it won't change under us. + * NB: when the buffer is backed up, we DO NOT insert the data pointed to by + * this XLogRecData struct into the XLOG record, since we assume it's present + * in the buffer. Therefore, rmgr redo routines MUST pay attention to + * XLR_BKP_BLOCK_X to know what is actually stored in the XLOG record. + * The i'th XLR_BKP_BLOCK bit corresponds to the i'th distinct buffer + * value (ignoring InvalidBuffer) appearing in the rdata chain. + * + * When buffer is valid, caller must set buffer_std to indicate whether the + * page uses standard pd_lower/pd_upper header fields. If this is true, then + * XLOG is allowed to omit the free space between pd_lower and pd_upper from + * the backed-up page image. Note that even when buffer_std is false, the + * page MUST have an LSN field as its first eight bytes! + * + * Note: data can be NULL to indicate no rmgr data associated with this chain + * entry. This can be sensible (ie, not a wasted entry) if buffer is valid. + * The implication is that the buffer has been changed by the operation being + * logged, and so may need to be backed up, but the change can be redone using + * only information already present elsewhere in the XLOG entry. */ typedef struct XLogRecData { - Buffer buffer; /* buffer associated with this data */ - char *data; - uint32 len; - struct XLogRecData *next; + char *data; /* start of rmgr data to include */ + uint32 len; /* length of rmgr data to include */ + Buffer buffer; /* buffer associated with data, if any */ + bool buffer_std; /* buffer has standard pd_lower/pd_upper */ + struct XLogRecData *next; /* next struct in chain, or NULL */ } XLogRecData; extern TimeLineID ThisTimeLineID; /* current TLI */ |