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Rework WAL-reading supporting structs

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The state-tracking of WAL reading in various places was pretty messy,
mostly because the ancient physical-replication WAL reading code wasn't
using the XLogReader abstraction.  This led to some untidy code.  Make
it prettier by creating two additional supporting structs,
WALSegmentContext and WALOpenSegment which keep track of WAL-reading
state.  This makes code cleaner, as well as supports more future
cleanup.

Author: Antonin Houska
Reviewed-by: Álvaro Herrera and (older versions) Robert Haas
Discussion: https://postgr.es/m/14984.1554998742@spoje.net
This commit is contained in:
Alvaro Herrera
2019-09-24 16:08:31 -03:00
parent a9ae99d019
commit 709d003fbd
12 changed files with 189 additions and 179 deletions
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41
src/include/access/xlogreader.h
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@ -31,6 +31,22 @@
#include "access/xlogrecord.h"
/* WALOpenSegment represents a WAL segment being read. */
typedef struct WALOpenSegment
{
int ws_file; /* segment file descriptor */
XLogSegNo ws_segno; /* segment number */
uint32 ws_off; /* offset in the segment */
TimeLineID ws_tli; /* timeline ID of the currently open file */
} WALOpenSegment;
/* WALSegmentContext carries context information about WAL segments to read */
typedef struct WALSegmentContext
{
char ws_dir[MAXPGPATH];
int ws_segsize;
} WALSegmentContext;
typedef struct XLogReaderState XLogReaderState;
/* Function type definition for the read_page callback */
@ -38,8 +54,7 @@ typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader,
XLogRecPtr targetPagePtr,
int reqLen,
XLogRecPtr targetRecPtr,
char *readBuf,
TimeLineID *pageTLI);
char *readBuf);
typedef struct
{
@ -77,11 +92,6 @@ struct XLogReaderState
* ----------------------------------------
*/
/*
* Segment size of the to-be-parsed data (mandatory).
*/
int wal_segment_size;
/*
* Data input callback (mandatory).
*
@ -99,9 +109,8 @@ struct XLogReaderState
* 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.
* The callback shall set ->seg.ws_tli to the TLI of the file the page was
* read from.
*/
XLogPageReadCB read_page;
@ -156,10 +165,9 @@ struct XLogReaderState
char *readBuf;
uint32 readLen;
/* last read segment, segment offset, TLI for data currently in readBuf */
XLogSegNo readSegNo;
uint32 readOff;
TimeLineID readPageTLI;
/* last read XLOG position for data currently in readBuf */
WALSegmentContext segcxt;
WALOpenSegment seg;
/*
* beginning of prior page read, and its TLI. Doesn't necessarily
@ -202,12 +210,17 @@ struct XLogReaderState
/* Get a new XLogReader */
extern XLogReaderState *XLogReaderAllocate(int wal_segment_size,
const char *waldir,
XLogPageReadCB pagereadfunc,
void *private_data);
/* Free an XLogReader */
extern void XLogReaderFree(XLogReaderState *state);
/* Initialize supporting structures */
extern void WALOpenSegmentInit(WALOpenSegment *seg, WALSegmentContext *segcxt,
int segsize, const char *waldir);
/* Read the next XLog record. Returns NULL on end-of-WAL or failure */
extern struct XLogRecord *XLogReadRecord(XLogReaderState *state,
XLogRecPtr recptr, char **errormsg);