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/*-------------------------------------------------------------------------
*
* xlogreader.h
* Definitions for the generic XLog reading facility
*
* Portions Copyright (c) 2013, PostgreSQL Global Development Group
*
* IDENTIFICATION
* src/include/access/xlogreader.h
*
* NOTES
* See the definition of the XLogReaderState struct for instructions on
* how to use the XLogReader infrastructure.
*
* The basic idea is to allocate an XLogReaderState via
* XLogReaderAllocate(), and call XLogReadRecord() until it returns NULL.
*-------------------------------------------------------------------------
*/
#ifndef XLOGREADER_H
#define XLOGREADER_H
#include "access/xlog_internal.h"
typedef struct XLogReaderState XLogReaderState;
/* Function type definition for the read_page callback */
typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader,
XLogRecPtr targetPagePtr,
int reqLen,
XLogRecPtr targetRecPtr,
char *readBuf,
TimeLineID *pageTLI);
struct XLogReaderState
{
/* ----------------------------------------
* Public parameters
* ----------------------------------------
*/
/*
* Data input callback (mandatory).
*
* This callback shall read at least reqLen valid bytes of the xlog page
* starting at targetPagePtr, and store them in readBuf. The callback
* shall return the number of bytes read (never more than XLOG_BLCKSZ), or
* -1 on failure. The callback shall sleep, if necessary, to wait for the
* requested bytes to become available. The callback will not be invoked
* again for the same page unless more than the returned number of bytes
* are needed.
*
* targetRecPtr is the position of the WAL record we're reading. Usually
* it is equal to targetPagePtr + reqLen, but sometimes xlogreader needs
* to read and verify the page or segment header, before it reads the
* actual WAL record it's interested in. In that case, targetRecPtr can
* be used to determine which timeline to read the page from.
*
* The callback shall set *pageTLI to the TLI of the file the page was
* read from. It is currently used only for error reporting purposes, to
* reconstruct the name of the WAL file where an error occurred.
*/
XLogPageReadCB read_page;
/*
* System identifier of the xlog files we're about to read. Set to zero
* (the default value) if unknown or unimportant.
*/
uint64 system_identifier;
/*
* Opaque data for callbacks to use. Not used by XLogReader.
*/
void *private_data;
/*
* Start and end point of last record read. EndRecPtr is also used as the
* position to read next, if XLogReadRecord receives an invalid recptr.
*/
XLogRecPtr ReadRecPtr; /* start of last record read */
XLogRecPtr EndRecPtr; /* end+1 of last record read */
/* ----------------------------------------
* private/internal state
* ----------------------------------------
*/
/* Buffer for currently read page (XLOG_BLCKSZ bytes) */
char *readBuf;
/* last read segment, segment offset, read length, TLI */
XLogSegNo readSegNo;
uint32 readOff;
uint32 readLen;
TimeLineID readPageTLI;
/* beginning of last page read, and its TLI */
XLogRecPtr latestPagePtr;
TimeLineID latestPageTLI;
/* beginning of the WAL record being read. */
XLogRecPtr currRecPtr;
/* Buffer for current ReadRecord result (expandable) */
char *readRecordBuf;
uint32 readRecordBufSize;
/* Buffer to hold error message */
char *errormsg_buf;
};
/* Get a new XLogReader */
extern XLogReaderState *XLogReaderAllocate(XLogPageReadCB pagereadfunc,
void *private_data);
/* Free an XLogReader */
extern void XLogReaderFree(XLogReaderState *state);
/* Read the next XLog record. Returns NULL on end-of-WAL or failure */
extern struct XLogRecord *XLogReadRecord(XLogReaderState *state,
XLogRecPtr recptr, char **errormsg);
#ifdef FRONTEND
extern XLogRecPtr XLogFindNextRecord(XLogReaderState *state, XLogRecPtr RecPtr);
#endif /* FRONTEND */
#endif /* XLOGREADER_H */
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