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/*-------------------------------------------------------------------------
*
* slru.h
* Simple LRU buffering for transaction status logfiles
*
* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* $PostgreSQL: pgsql/src/include/access/slru.h,v 1.18 2006/03/05 15:58:53 momjian Exp $
*
*-------------------------------------------------------------------------
*/
#ifndef SLRU_H
#define SLRU_H
#include "storage/lwlock.h"
/*
* Page status codes. Note that these do not include the "dirty" bit.
* page_dirty can be TRUE only in the VALID or WRITE_IN_PROGRESS states;
* in the latter case it implies that the page has been re-dirtied since
* the write started.
*/
typedef enum
{
SLRU_PAGE_EMPTY, /* buffer is not in use */
SLRU_PAGE_READ_IN_PROGRESS, /* page is being read in */
SLRU_PAGE_VALID, /* page is valid and not being written */
SLRU_PAGE_WRITE_IN_PROGRESS /* page is being written out */
} SlruPageStatus;
/*
* Shared-memory state
*/
typedef struct SlruSharedData
{
LWLockId ControlLock;
/* Number of buffers managed by this SLRU structure */
int num_slots;
/*
* Arrays holding info for each buffer slot. Page number is undefined
* when status is EMPTY, as is page_lru_count.
*/
char **page_buffer;
SlruPageStatus *page_status;
bool *page_dirty;
int *page_number;
int *page_lru_count;
LWLockId *buffer_locks;
/*----------
* We mark a page "most recently used" by setting
* page_lru_count[slotno] = ++cur_lru_count;
* The oldest page is therefore the one with the highest value of
* cur_lru_count - page_lru_count[slotno]
* The counts will eventually wrap around, but this calculation still
* works as long as no page's age exceeds INT_MAX counts.
*----------
*/
int cur_lru_count;
/*
* 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(int nslots);
extern void SimpleLruInit(SlruCtl ctl, const char *name, int nslots,
LWLockId ctllock, const char *subdir);
extern int SimpleLruZeroPage(SlruCtl ctl, int pageno);
extern int SimpleLruReadPage(SlruCtl ctl, int pageno, TransactionId xid);
extern int SimpleLruReadPage_ReadOnly(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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