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PostgreSQL/src/include/access/xlog.h
Tom Lane d526575f89 Make large sequential scans and VACUUMs work in a limited-size "ring" of 
buffers, rather than blowing out the whole shared-buffer arena.  Aside from
avoiding cache spoliation, this fixes the problem that VACUUM formerly tended
to cause a WAL flush for every page it modified, because we had it hacked to
use only a single buffer.  Those flushes will now occur only once per
ring-ful.  The exact ring size, and the threshold for seqscans to switch into
the ring usage pattern, remain under debate; but the infrastructure seems
done.  The key bit of infrastructure is a new optional BufferAccessStrategy
object that can be passed to ReadBuffer operations; this replaces the former
StrategyHintVacuum API.

This patch also changes the buffer usage-count methodology a bit: we now
advance usage_count when first pinning a buffer, rather than when last
unpinning it.  To preserve the behavior that a buffer's lifetime starts to
decrease when it's released, the clock sweep code is modified to not decrement
usage_count of pinned buffers.

Work not done in this commit: teach GiST and GIN indexes to use the vacuum
BufferAccessStrategy for vacuum-driven fetches.

Original patch by Simon, reworked by Heikki and again by Tom.
2007-05-30 20:12:03 +00:00

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/*
* xlog.h
*
* PostgreSQL transaction log manager
*
* Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/xlog.h,v 1.78 2007/05/30 20:12:02 tgl Exp $
*/
#ifndef XLOG_H
#define XLOG_H
#include "access/rmgr.h"
#include "access/xlogdefs.h"
#include "lib/stringinfo.h"
#include "storage/buf.h"
#include "utils/pg_crc.h"
/*
* The overall layout of an XLOG record is:
* Fixed-size header (XLogRecord struct)
* rmgr-specific data
* BkpBlock
* backup block data
* BkpBlock
* backup block data
* ...
*
* where there can be zero to three backup blocks (as signaled by xl_info flag
* bits). XLogRecord structs always start on MAXALIGN boundaries in the WAL
* files, and we round up SizeOfXLogRecord so that the rmgr data is also
* guaranteed to begin on a MAXALIGN boundary. However, no padding is added
* to align BkpBlock structs or backup block data.
*
* NOTE: xl_len counts only the rmgr data, not the XLogRecord header,
* and also not any backup blocks. xl_tot_len counts everything. Neither
* length field is rounded up to an alignment boundary.
*/
typedef struct XLogRecord
{
pg_crc32 xl_crc; /* CRC for this record */
XLogRecPtr xl_prev; /* ptr to previous record in log */
TransactionId xl_xid; /* xact id */
uint32 xl_tot_len; /* total len of entire record */
uint32 xl_len; /* total len of rmgr data */
uint8 xl_info; /* flag bits, see below */
RmgrId xl_rmid; /* resource manager for this record */
/* Depending on MAXALIGN, there are either 2 or 6 wasted bytes here */
/* ACTUAL LOG DATA FOLLOWS AT END OF STRUCT */
} XLogRecord;
#define SizeOfXLogRecord MAXALIGN(sizeof(XLogRecord))
#define XLogRecGetData(record) ((char*) (record) + SizeOfXLogRecord)
/*
* XLOG uses only low 4 bits of xl_info. High 4 bits may be used by rmgr.
*/
#define XLR_INFO_MASK 0x0F
/*
* If we backed up any disk blocks with the XLOG record, we use flag bits in
* xl_info to signal it. We support backup of up to 3 disk blocks per XLOG
* record.
*/
#define XLR_BKP_BLOCK_MASK 0x0E /* all info bits used for bkp blocks */
#define XLR_MAX_BKP_BLOCKS 3
#define XLR_SET_BKP_BLOCK(iblk) (0x08 >> (iblk))
#define XLR_BKP_BLOCK_1 XLR_SET_BKP_BLOCK(0) /* 0x08 */
#define XLR_BKP_BLOCK_2 XLR_SET_BKP_BLOCK(1) /* 0x04 */
#define XLR_BKP_BLOCK_3 XLR_SET_BKP_BLOCK(2) /* 0x02 */
/*
* Bit 0 of xl_info is set if the backed-up blocks could safely be removed
* from a compressed version of XLOG (that is, they are backed up only to
* prevent partial-page-write problems, and not to ensure consistency of PITR
* recovery). The compression algorithm would need to extract data from the
* blocks to create an equivalent non-full-page XLOG record.
*/
#define XLR_BKP_REMOVABLE 0x01
/*
* Sometimes we log records which are out of transaction control.
* Rmgr may "or" XLOG_NO_TRAN into info passed to XLogInsert to indicate this.
*/
#define XLOG_NO_TRAN XLR_INFO_MASK
/* Sync methods */
#define SYNC_METHOD_FSYNC 0
#define SYNC_METHOD_FDATASYNC 1
#define SYNC_METHOD_OPEN 2 /* for O_SYNC and O_DSYNC */
#define SYNC_METHOD_FSYNC_WRITETHROUGH 3
extern int sync_method;
/*
* 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 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
{
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 */
extern bool InRecovery;
extern XLogRecPtr MyLastRecPtr;
extern bool MyXactMadeXLogEntry;
extern bool MyXactMadeTempRelUpdate;
extern XLogRecPtr ProcLastRecEnd;
/* these variables are GUC parameters related to XLOG */
extern int CheckPointSegments;
extern int XLOGbuffers;
extern char *XLogArchiveCommand;
extern int XLogArchiveTimeout;
extern char *XLOG_sync_method;
extern const char XLOG_sync_method_default[];
#define XLogArchivingActive() (XLogArchiveCommand[0] != '\0')
#ifdef WAL_DEBUG
extern bool XLOG_DEBUG;
#endif
extern XLogRecPtr XLogInsert(RmgrId rmid, uint8 info, XLogRecData *rdata);
extern void XLogFlush(XLogRecPtr RecPtr);
extern bool XLogNeedsFlush(XLogRecPtr RecPtr);
extern void xlog_redo(XLogRecPtr lsn, XLogRecord *record);
extern void xlog_desc(StringInfo buf, uint8 xl_info, char *rec);
extern void UpdateControlFile(void);
extern Size XLOGShmemSize(void);
extern void XLOGShmemInit(void);
extern void BootStrapXLOG(void);
extern void StartupXLOG(void);
extern void ShutdownXLOG(int code, Datum arg);
extern void InitXLOGAccess(void);
extern void CreateCheckPoint(bool shutdown, bool force);
extern void XLogPutNextOid(Oid nextOid);
extern XLogRecPtr GetRedoRecPtr(void);
extern void GetNextXidAndEpoch(TransactionId *xid, uint32 *epoch);
#endif /* XLOG_H */
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