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postgresql/src/include/access/xlogprefetcher.h

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Prefetch data referenced by the WAL, take II. Introduce a new GUC recovery_prefetch. When enabled, look ahead in the WAL and try to initiate asynchronous reading of referenced data blocks that are not yet cached in our buffer pool. For now, this is done with posix_fadvise(), which has several caveats. Since not all OSes have that system call, "try" is provided so that it can be enabled where available. Better mechanisms for asynchronous I/O are possible in later work. Set to "try" for now for test coverage. Default setting to be finalized before release. The GUC wal_decode_buffer_size limits the distance we can look ahead in bytes of decoded data. The existing GUC maintenance_io_concurrency is used to limit the number of concurrent I/Os allowed, based on pessimistic heuristics used to infer that I/Os have begun and completed. We'll also not look more than maintenance_io_concurrency * 4 block references ahead. Reviewed-by: Julien Rouhaud <rjuju123@gmail.com> Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com> Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com> (earlier version) Reviewed-by: Andres Freund <andres@anarazel.de> (earlier version) Reviewed-by: Justin Pryzby <pryzby@telsasoft.com> (earlier version) Tested-by: Tomas Vondra <tomas.vondra@2ndquadrant.com> (earlier version) Tested-by: Jakub Wartak <Jakub.Wartak@tomtom.com> (earlier version) Tested-by: Dmitry Dolgov <9erthalion6@gmail.com> (earlier version) Tested-by: Sait Talha Nisanci <Sait.Nisanci@microsoft.com> (earlier version) Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com
2022-04-07 09:28:40 +02:00
/*-------------------------------------------------------------------------
*
* xlogprefetcher.h
* Declarations for the recovery prefetching module.
*
* Portions Copyright (c) 2022, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/include/access/xlogprefetcher.h
*-------------------------------------------------------------------------
*/
#ifndef XLOGPREFETCHER_H
#define XLOGPREFETCHER_H
#include "access/xlogdefs.h"
Include some missing headers. Per headerscheck on BF animal crake, and Andres. Discussion: https://postgr.es/m/20220407083630.n62vgwqfy2v6wsrd%40alap3.anarazel.de
2022-04-07 10:55:16 +02:00
#include "access/xlogreader.h"
#include "access/xlogrecord.h"
Prefetch data referenced by the WAL, take II. Introduce a new GUC recovery_prefetch. When enabled, look ahead in the WAL and try to initiate asynchronous reading of referenced data blocks that are not yet cached in our buffer pool. For now, this is done with posix_fadvise(), which has several caveats. Since not all OSes have that system call, "try" is provided so that it can be enabled where available. Better mechanisms for asynchronous I/O are possible in later work. Set to "try" for now for test coverage. Default setting to be finalized before release. The GUC wal_decode_buffer_size limits the distance we can look ahead in bytes of decoded data. The existing GUC maintenance_io_concurrency is used to limit the number of concurrent I/Os allowed, based on pessimistic heuristics used to infer that I/Os have begun and completed. We'll also not look more than maintenance_io_concurrency * 4 block references ahead. Reviewed-by: Julien Rouhaud <rjuju123@gmail.com> Reviewed-by: Tomas Vondra <tomas.vondra@2ndquadrant.com> Reviewed-by: Alvaro Herrera <alvherre@2ndquadrant.com> (earlier version) Reviewed-by: Andres Freund <andres@anarazel.de> (earlier version) Reviewed-by: Justin Pryzby <pryzby@telsasoft.com> (earlier version) Tested-by: Tomas Vondra <tomas.vondra@2ndquadrant.com> (earlier version) Tested-by: Jakub Wartak <Jakub.Wartak@tomtom.com> (earlier version) Tested-by: Dmitry Dolgov <9erthalion6@gmail.com> (earlier version) Tested-by: Sait Talha Nisanci <Sait.Nisanci@microsoft.com> (earlier version) Discussion: https://postgr.es/m/CA%2BhUKGJ4VJN8ttxScUFM8dOKX0BrBiboo5uz1cq%3DAovOddfHpA%40mail.gmail.com
2022-04-07 09:28:40 +02:00
/* GUCs */
extern int recovery_prefetch;
/* Possible values for recovery_prefetch */
typedef enum
{
RECOVERY_PREFETCH_OFF,
RECOVERY_PREFETCH_ON,
RECOVERY_PREFETCH_TRY
} RecoveryPrefetchValue;
struct XLogPrefetcher;
typedef struct XLogPrefetcher XLogPrefetcher;
extern void XLogPrefetchReconfigure(void);
extern size_t XLogPrefetchShmemSize(void);
extern void XLogPrefetchShmemInit(void);
extern void XLogPrefetchResetStats(void);
extern XLogPrefetcher *XLogPrefetcherAllocate(XLogReaderState *reader);
extern void XLogPrefetcherFree(XLogPrefetcher *prefetcher);
extern XLogReaderState *XLogPrefetcherGetReader(XLogPrefetcher *prefetcher);
extern void XLogPrefetcherBeginRead(XLogPrefetcher *prefetcher,
XLogRecPtr recPtr);
extern XLogRecord *XLogPrefetcherReadRecord(XLogPrefetcher *prefetcher,
char **errmsg);
extern void XLogPrefetcherComputeStats(XLogPrefetcher *prefetcher);
#endif