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/*-------------------------------------------------------------------------
*
* slru.h
* Simple LRU buffering for transaction status logfiles
*
* Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/slru.h,v 1.14 2005/10/15 02:49:42 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef SLRU_H
#define SLRU_H
#include "storage/lwlock.h"
/*
* Number of page buffers. Ideally this could be different for CLOG and
* SUBTRANS, but the benefit doesn't seem to be worth any additional
* notational cruft.
*/
#define NUM_SLRU_BUFFERS 8
/* Page status codes */
typedef enum
{
SLRU_PAGE_EMPTY, /* buffer is not in use */
SLRU_PAGE_READ_IN_PROGRESS, /* page is being read in */
SLRU_PAGE_CLEAN, /* page is valid and not dirty */
SLRU_PAGE_DIRTY, /* page is valid but needs write */
SLRU_PAGE_WRITE_IN_PROGRESS /* page is being written out */
} SlruPageStatus;
/*
* Shared-memory state
*/
typedef struct SlruSharedData
{
LWLockId ControlLock;
/*
* Info for each buffer slot. Page number is undefined when status is
* EMPTY. lru_count is essentially the number of page switches since last
* use of this page; the page with highest lru_count is the best candidate
* to replace.
*/
char *page_buffer[NUM_SLRU_BUFFERS];
SlruPageStatus page_status[NUM_SLRU_BUFFERS];
int page_number[NUM_SLRU_BUFFERS];
unsigned int page_lru_count[NUM_SLRU_BUFFERS];
LWLockId buffer_locks[NUM_SLRU_BUFFERS];
/*
* latest_page_number is the page number of the current end of the log;
* this is not critical data, since we use it only to avoid swapping out
* the latest page.
*/
int latest_page_number;
} SlruSharedData;
typedef SlruSharedData *SlruShared;
/*
* SlruCtlData is an unshared structure that points to the active information
* in shared memory.
*/
typedef struct SlruCtlData
{
SlruShared shared;
/*
* This flag tells whether to fsync writes (true for pg_clog, false for
* pg_subtrans).
*/
bool do_fsync;
/*
* Decide which of two page numbers is "older" for truncation purposes. We
* need to use comparison of TransactionIds here in order to do the right
* thing with wraparound XID arithmetic.
*/
bool (*PagePrecedes) (int, int);
/*
* Dir is set during SimpleLruInit and does not change thereafter. Since
* it's always the same, it doesn't need to be in shared memory.
*/
char Dir[64];
} SlruCtlData;
typedef SlruCtlData *SlruCtl;
/* Opaque struct known only in slru.c */
typedef struct SlruFlushData *SlruFlush;
extern Size SimpleLruShmemSize(void);
extern void SimpleLruInit(SlruCtl ctl, const char *name,
LWLockId ctllock, const char *subdir);
extern int SimpleLruZeroPage(SlruCtl ctl, int pageno);
extern int SimpleLruReadPage(SlruCtl ctl, int pageno, TransactionId xid);
extern void SimpleLruWritePage(SlruCtl ctl, int slotno, SlruFlush fdata);
extern void SimpleLruFlush(SlruCtl ctl, bool checkpoint);
extern void SimpleLruTruncate(SlruCtl ctl, int cutoffPage);
extern bool SlruScanDirectory(SlruCtl ctl, int cutoffPage, bool doDeletions);
#endif /* SLRU_H */
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