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Rework XLogReader callback system

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Code review for 0dc8ead463, prompted by a bug closed by 91c40548d5.

XLogReader's system for opening and closing segments had gotten too
complicated, with callbacks being passed at both the XLogReaderAllocate
level (read_page) as well as at the WALRead level (segment_open).  This
was confusing and hard to follow, so restructure things so that these
callbacks are passed together at XLogReaderAllocate time, and add
another callback to the set (segment_close) to make it a coherent whole.
Also, ensure XLogReaderState is an argument to all the callbacks, so
that they can grab at the ->private data if necessary.

Document the whole arrangement more clearly.

Author: Álvaro Herrera <alvherre@alvh.no-ip.org>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/20200422175754.GA19858@alvherre.pgsql
This commit is contained in:
Alvaro Herrera
2020-05-08 15:30:34 -04:00
parent 871696ba20
commit b060dbe000
13 changed files with 214 additions and 113 deletions
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51
src/backend/access/transam/xlogreader.c
View File

@ -71,7 +71,7 @@ report_invalid_record(XLogReaderState *state, const char *fmt,...)
*/
XLogReaderState *
XLogReaderAllocate(int wal_segment_size, const char *waldir,
XLogPageReadCB pagereadfunc, void *private_data)
XLogReaderRoutine *routine, void *private_data)
{
XLogReaderState *state;
@ -81,6 +81,9 @@ XLogReaderAllocate(int wal_segment_size, const char *waldir,
if (!state)
return NULL;
/* initialize caller-provided support functions */
state->routine = *routine;
state->max_block_id = -1;
/*
@ -102,7 +105,6 @@ XLogReaderAllocate(int wal_segment_size, const char *waldir,
WALOpenSegmentInit(&state->seg, &state->segcxt, wal_segment_size,
waldir);
state->read_page = pagereadfunc;
/* system_identifier initialized to zeroes above */
state->private_data = private_data;
/* ReadRecPtr, EndRecPtr and readLen initialized to zeroes above */
@ -137,7 +139,7 @@ XLogReaderFree(XLogReaderState *state)
int block_id;
if (state->seg.ws_file != -1)
close(state->seg.ws_file);
state->routine.segment_close(state);
for (block_id = 0; block_id <= XLR_MAX_BLOCK_ID; block_id++)
{
@ -250,7 +252,7 @@ XLogBeginRead(XLogReaderState *state, XLogRecPtr RecPtr)
* XLogBeginRead() or XLogFindNextRecord() must be called before the first call
* to XLogReadRecord().
*
* If the read_page callback fails to read the requested data, NULL is
* If the page_read callback fails to read the requested data, NULL is
* returned. The callback is expected to have reported the error; errormsg
* is set to NULL.
*
@ -559,10 +561,10 @@ err:
/*
* Read a single xlog page including at least [pageptr, reqLen] of valid data
* via the read_page() callback.
* via the page_read() callback.
*
* Returns -1 if the required page cannot be read for some reason; errormsg_buf
* is set in that case (unless the error occurs in the read_page callback).
* is set in that case (unless the error occurs in the page_read callback).
*
* We fetch the page from a reader-local cache if we know we have the required
* data and if there hasn't been any error since caching the data.
@ -589,7 +591,7 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
* Data is not in our buffer.
*
* Every time we actually read the segment, even if we looked at parts of
* it before, we need to do verification as the read_page callback might
* it before, we need to do verification as the page_read callback might
* now be rereading data from a different source.
*
* Whenever switching to a new WAL segment, we read the first page of the
@ -601,9 +603,9 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
{
XLogRecPtr targetSegmentPtr = pageptr - targetPageOff;
readLen = state->read_page(state, targetSegmentPtr, XLOG_BLCKSZ,
state->currRecPtr,
state->readBuf);
readLen = state->routine.page_read(state, targetSegmentPtr, XLOG_BLCKSZ,
state->currRecPtr,
state->readBuf);
if (readLen < 0)
goto err;
@ -619,9 +621,9 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
* First, read the requested data length, but at least a short page header
* so that we can validate it.
*/
readLen = state->read_page(state, pageptr, Max(reqLen, SizeOfXLogShortPHD),
state->currRecPtr,
state->readBuf);
readLen = state->routine.page_read(state, pageptr, Max(reqLen, SizeOfXLogShortPHD),
state->currRecPtr,
state->readBuf);
if (readLen < 0)
goto err;
@ -638,9 +640,9 @@ ReadPageInternal(XLogReaderState *state, XLogRecPtr pageptr, int reqLen)
/* still not enough */
if (readLen < XLogPageHeaderSize(hdr))
{
readLen = state->read_page(state, pageptr, XLogPageHeaderSize(hdr),
state->currRecPtr,
state->readBuf);
readLen = state->routine.page_read(state, pageptr, XLogPageHeaderSize(hdr),
state->currRecPtr,
state->readBuf);
if (readLen < 0)
goto err;
}
@ -1041,11 +1043,14 @@ err:
#endif /* FRONTEND */
/*
* Helper function to ease writing of XLogRoutine->page_read callbacks.
* If this function is used, caller must supply an open_segment callback in
* 'state', as that is used here.
*
* Read 'count' bytes into 'buf', starting at location 'startptr', from WAL
* fetched from timeline 'tli'.
*
* 'seg/segcxt' identify the last segment used. 'openSegment' is a callback
* to open the next segment, if necessary.
* 'seg/segcxt' identify the last segment used.
*
* Returns true if succeeded, false if an error occurs, in which case
* 'errinfo' receives error details.
@ -1054,9 +1059,10 @@ err:
* WAL buffers when possible.
*/
bool
WALRead(char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
WALRead(XLogReaderState *state,
char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
WALOpenSegment *seg, WALSegmentContext *segcxt,
WALSegmentOpen openSegment, WALReadError *errinfo)
WALReadError *errinfo)
{
char *p;
XLogRecPtr recptr;
@ -1086,10 +1092,11 @@ WALRead(char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
XLogSegNo nextSegNo;
if (seg->ws_file >= 0)
close(seg->ws_file);
state->routine.segment_close(state);
XLByteToSeg(recptr, nextSegNo, segcxt->ws_segsize);
seg->ws_file = openSegment(nextSegNo, segcxt, &tli);
seg->ws_file = state->routine.segment_open(state, nextSegNo,
segcxt, &tli);
/* Update the current segment info. */
seg->ws_tli = tli;