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/*
* xloginsert.h
*
* Functions for generating WAL records
*
* Portions Copyright (c) 1996-2014, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* src/include/access/xloginsert.h
*/
#ifndef XLOGINSERT_H
#define XLOGINSERT_H
#include "access/rmgr.h"
#include "access/xlogdefs.h"
#include "storage/block.h"
#include "storage/buf.h"
#include "storage/relfilenode.h"
/*
* 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(N) bit in xl_info. Note that the buffer must be pinned
* 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(N) to know what is actually stored in the XLOG record.
* The N'th XLR_BKP_BLOCK bit corresponds to the N'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
{
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 XLogRecPtr XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata);
extern XLogRecPtr log_newpage(RelFileNode *rnode, ForkNumber forkNum,
BlockNumber blk, char *page, bool page_std);
extern XLogRecPtr log_newpage_buffer(Buffer buffer, bool page_std);
extern XLogRecPtr XLogSaveBufferForHint(Buffer buffer, bool buffer_std);
extern bool XLogCheckBufferNeedsBackup(Buffer buffer);
#endif /* XLOGINSERT_H */
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