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121 lines
3.5 KiB
C
121 lines
3.5 KiB
C
/*-------------------------------------------------------------------------
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*
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* slru.h
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* Simple LRU buffering for transaction status logfiles
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*
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* Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
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* Portions Copyright (c) 1994, Regents of the University of California
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*
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* $PostgreSQL: pgsql/src/include/access/slru.h,v 1.18 2006/03/05 15:58:53 momjian Exp $
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*
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*-------------------------------------------------------------------------
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*/
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#ifndef SLRU_H
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#define SLRU_H
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#include "storage/lwlock.h"
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/*
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* Page status codes. Note that these do not include the "dirty" bit.
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* page_dirty can be TRUE only in the VALID or WRITE_IN_PROGRESS states;
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* in the latter case it implies that the page has been re-dirtied since
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* the write started.
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*/
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typedef enum
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{
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SLRU_PAGE_EMPTY, /* buffer is not in use */
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SLRU_PAGE_READ_IN_PROGRESS, /* page is being read in */
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SLRU_PAGE_VALID, /* page is valid and not being written */
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SLRU_PAGE_WRITE_IN_PROGRESS /* page is being written out */
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} SlruPageStatus;
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/*
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* Shared-memory state
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*/
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typedef struct SlruSharedData
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{
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LWLockId ControlLock;
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/* Number of buffers managed by this SLRU structure */
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int num_slots;
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/*
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* Arrays holding info for each buffer slot. Page number is undefined
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* when status is EMPTY, as is page_lru_count.
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*/
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char **page_buffer;
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SlruPageStatus *page_status;
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bool *page_dirty;
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int *page_number;
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int *page_lru_count;
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LWLockId *buffer_locks;
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/*----------
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* We mark a page "most recently used" by setting
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* page_lru_count[slotno] = ++cur_lru_count;
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* The oldest page is therefore the one with the highest value of
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* cur_lru_count - page_lru_count[slotno]
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* The counts will eventually wrap around, but this calculation still
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* works as long as no page's age exceeds INT_MAX counts.
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*----------
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*/
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int cur_lru_count;
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/*
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* latest_page_number is the page number of the current end of the log;
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* this is not critical data, since we use it only to avoid swapping out
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* the latest page.
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*/
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int latest_page_number;
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} SlruSharedData;
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typedef SlruSharedData *SlruShared;
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/*
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* SlruCtlData is an unshared structure that points to the active information
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* in shared memory.
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*/
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typedef struct SlruCtlData
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{
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SlruShared shared;
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/*
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* This flag tells whether to fsync writes (true for pg_clog, false for
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* pg_subtrans).
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*/
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bool do_fsync;
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/*
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* Decide which of two page numbers is "older" for truncation purposes. We
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* need to use comparison of TransactionIds here in order to do the right
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* thing with wraparound XID arithmetic.
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*/
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bool (*PagePrecedes) (int, int);
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/*
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* Dir is set during SimpleLruInit and does not change thereafter. Since
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* it's always the same, it doesn't need to be in shared memory.
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*/
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char Dir[64];
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} SlruCtlData;
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typedef SlruCtlData *SlruCtl;
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/* Opaque struct known only in slru.c */
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typedef struct SlruFlushData *SlruFlush;
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extern Size SimpleLruShmemSize(int nslots);
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extern void SimpleLruInit(SlruCtl ctl, const char *name, int nslots,
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LWLockId ctllock, const char *subdir);
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extern int SimpleLruZeroPage(SlruCtl ctl, int pageno);
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extern int SimpleLruReadPage(SlruCtl ctl, int pageno, TransactionId xid);
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extern int SimpleLruReadPage_ReadOnly(SlruCtl ctl, int pageno,
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TransactionId xid);
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extern void SimpleLruWritePage(SlruCtl ctl, int slotno, SlruFlush fdata);
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extern void SimpleLruFlush(SlruCtl ctl, bool checkpoint);
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extern void SimpleLruTruncate(SlruCtl ctl, int cutoffPage);
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extern bool SlruScanDirectory(SlruCtl ctl, int cutoffPage, bool doDeletions);
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#endif /* SLRU_H */
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