On 2020-May-08, Kyotaro Horiguchi wrote:
> I agree to the direction of this patch. Thanks for the explanation.
> The patch looks good to me except the two points below.
Thanks! I pushed the patch. I fixed the walsender commentary as you
suggested, but I'm still of the opinion that we might want to use the
XLogReader abstraction in physical walsender than work without it; if
nothing else, that would simplify WALRead's API.
I didn't change this one though:
> wal_segment_close(XlogReaderState *state) is setting
> state->seg.ws_file to -1. On the other hand wal_segment_close(state,..)
> doesn't update ws_file and the caller sets the returned value to
> (eventually) the same field.
>
> + seg->ws_file = state->routine.segment_open(state,
> nextSegNo,
> +
> segcxt, &tli);
>
> If you are willing to do so, I think it is better to make the callback
> functions are responsible to update the seg.ws_file and the callers
> don't care.
I agree that this would be a good idea, but it's more than just a
handful of lines of changes so I think we should consider it separately.
Attached as 0002. I also realized while doing this that we can further
simplify WALRead()'s API if we're willing to bend walsender a little bit
more into the fake xlogreader thing; that's 0001.
I marked the open item closed nonetheless.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
>From 600e28124ffb2741482bb096d5615b521ae83850 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date: Fri, 8 May 2020 16:40:24 -0400
Subject: [PATCH 1/2] fix WALRead API to take seg/segcxt from XLogReaderState
---
src/backend/access/transam/xlogreader.c | 31 +++++++++++--------------
src/backend/access/transam/xlogutils.c | 1 -
src/backend/replication/walsender.c | 6 ++---
src/bin/pg_waldump/pg_waldump.c | 1 -
src/include/access/xlogreader.h | 4 +---
5 files changed, 17 insertions(+), 26 deletions(-)
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 7cee8b92c9..f42dee2640 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1050,8 +1050,6 @@ err:
* Read 'count' bytes into 'buf', starting at location 'startptr', from WAL
* fetched from timeline 'tli'.
*
- * 'seg/segcxt' identify the last segment used.
- *
* Returns true if succeeded, false if an error occurs, in which case
* 'errinfo' receives error details.
*
@@ -1061,7 +1059,6 @@ err:
bool
WALRead(XLogReaderState *state,
char *buf, XLogRecPtr startptr, Size count, TimeLineID tli,
- WALOpenSegment *seg, WALSegmentContext *segcxt,
WALReadError *errinfo)
{
char *p;
@@ -1078,34 +1075,34 @@ WALRead(XLogReaderState *state,
int segbytes;
int readbytes;
- startoff = XLogSegmentOffset(recptr, segcxt->ws_segsize);
+ startoff = XLogSegmentOffset(recptr, state->segcxt.ws_segsize);
/*
* If the data we want is not in a segment we have open, close what we
* have (if anything) and open the next one, using the caller's
* provided openSegment callback.
*/
- if (seg->ws_file < 0 ||
- !XLByteInSeg(recptr, seg->ws_segno, segcxt->ws_segsize) ||
- tli != seg->ws_tli)
+ if (state->seg.ws_file < 0 ||
+ !XLByteInSeg(recptr, state->seg.ws_segno, state->segcxt.ws_segsize) ||
+ tli != state->seg.ws_tli)
{
XLogSegNo nextSegNo;
- if (seg->ws_file >= 0)
+ if (state->seg.ws_file >= 0)
state->routine.segment_close(state);
- XLByteToSeg(recptr, nextSegNo, segcxt->ws_segsize);
- seg->ws_file = state->routine.segment_open(state, nextSegNo,
- segcxt, &tli);
+ XLByteToSeg(recptr, nextSegNo, state->segcxt.ws_segsize);
+ state->seg.ws_file = state->routine.segment_open(state, nextSegNo,
+ &state->segcxt, &tli);
/* Update the current segment info. */
- seg->ws_tli = tli;
- seg->ws_segno = nextSegNo;
+ state->seg.ws_tli = tli;
+ state->seg.ws_segno = nextSegNo;
}
/* How many bytes are within this segment? */
- if (nbytes > (segcxt->ws_segsize - startoff))
- segbytes = segcxt->ws_segsize - startoff;
+ if (nbytes > (state->segcxt.ws_segsize - startoff))
+ segbytes = state->segcxt.ws_segsize - startoff;
else
segbytes = nbytes;
@@ -1115,7 +1112,7 @@ WALRead(XLogReaderState *state,
/* Reset errno first; eases reporting non-errno-affecting errors */
errno = 0;
- readbytes = pg_pread(seg->ws_file, p, segbytes, (off_t) startoff);
+ readbytes = pg_pread(state->seg.ws_file, p, segbytes, (off_t) startoff);
#ifndef FRONTEND
pgstat_report_wait_end();
@@ -1127,7 +1124,7 @@ WALRead(XLogReaderState *state,
errinfo->wre_req = segbytes;
errinfo->wre_read = readbytes;
errinfo->wre_off = startoff;
- errinfo->wre_seg = *seg;
+ errinfo->wre_seg = state->seg;
return false;
}
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index bbd801513a..fc0bb7d059 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -947,7 +947,6 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
* zero-padded up to the page boundary if it's incomplete.
*/
if (!WALRead(state, cur_page, targetPagePtr, XLOG_BLCKSZ, tli,
- &state->seg, &state->segcxt,
&errinfo))
WALReadRaiseError(&errinfo);
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index d18475b854..ed8c08cb6a 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -840,8 +840,6 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
sendSeg->ws_tli, /* Pass the current TLI because only
* WalSndSegmentOpen controls whether new
* TLI is needed. */
- sendSeg,
- sendCxt,
&errinfo))
WALReadRaiseError(&errinfo);
@@ -2760,6 +2758,8 @@ XLogSendPhysical(void)
enlargeStringInfo(&output_message, nbytes);
retry:
+ fake_xlogreader.seg = *sendSeg;
+ fake_xlogreader.segcxt = *sendCxt;
if (!WALRead(&fake_xlogreader,
&output_message.data[output_message.len],
startptr,
@@ -2767,8 +2767,6 @@ retry:
sendSeg->ws_tli, /* Pass the current TLI because only
* WalSndSegmentOpen controls whether new
* TLI is needed. */
- sendSeg,
- sendCxt,
&errinfo))
WALReadRaiseError(&errinfo);
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index e29f65500f..46734914b7 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -356,7 +356,6 @@ WALDumpReadPage(XLogReaderState *state, XLogRecPtr targetPagePtr, int reqLen,
}
if (!WALRead(state, readBuff, targetPagePtr, count, private->timeline,
- &state->seg, &state->segcxt,
&errinfo))
{
WALOpenSegment *seg = &errinfo.wre_seg;
diff --git a/src/include/access/xlogreader.h b/src/include/access/xlogreader.h
index 81af200f5e..e77f478d68 100644
--- a/src/include/access/xlogreader.h
+++ b/src/include/access/xlogreader.h
@@ -301,9 +301,7 @@ typedef struct WALReadError
extern bool WALRead(XLogReaderState *state,
char *buf, XLogRecPtr startptr, Size count,
- TimeLineID tli, WALOpenSegment *seg,
- WALSegmentContext *segcxt,
- WALReadError *errinfo);
+ TimeLineID tli, WALReadError *errinfo);
/* Functions for decoding an XLogRecord */
--
2.20.1
>From 721cadab3f1ab88c7b2f12ed2ede5dd3c9455856 Mon Sep 17 00:00:00 2001
From: Alvaro Herrera <alvhe...@alvh.no-ip.org>
Date: Fri, 8 May 2020 17:03:09 -0400
Subject: [PATCH 2/2] Simplify XLogReader's open_segment API
Instead of returning the file descriptor, install it directly in
XLogReaderState->seg.ws_file.
---
src/backend/access/transam/xlogreader.c | 4 ++--
src/backend/access/transam/xlogutils.c | 32 ++++++++++++-------------
src/backend/replication/walsender.c | 12 ++++------
src/bin/pg_waldump/pg_waldump.c | 9 ++++---
src/include/access/xlogreader.h | 12 +++++-----
src/include/access/xlogutils.h | 2 +-
6 files changed, 33 insertions(+), 38 deletions(-)
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index f42dee2640..a533241370 100644
--- a/src/backend/access/transam/xlogreader.c
+++ b/src/backend/access/transam/xlogreader.c
@@ -1092,8 +1092,8 @@ WALRead(XLogReaderState *state,
state->routine.segment_close(state);
XLByteToSeg(recptr, nextSegNo, state->segcxt.ws_segsize);
- state->seg.ws_file = state->routine.segment_open(state, nextSegNo,
- &state->segcxt, &tli);
+ state->routine.segment_open(state, nextSegNo, &state->segcxt, &tli);
+ Assert(state->seg.ws_file >= 0); /* shouldn't happen */
/* Update the current segment info. */
state->seg.ws_tli = tli;
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index fc0bb7d059..1cc2c624a4 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -784,7 +784,7 @@ XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wa
}
/* XLogReaderRoutine->segment_open callback for local pg_wal files */
-int
+void
wal_segment_open(XLogReaderState *state, XLogSegNo nextSegNo,
WALSegmentContext *segcxt, TimeLineID *tli_p)
{
@@ -793,22 +793,20 @@ wal_segment_open(XLogReaderState *state, XLogSegNo nextSegNo,
int fd;
XLogFilePath(path, tli, nextSegNo, segcxt->ws_segsize);
- fd = BasicOpenFile(path, O_RDONLY | PG_BINARY);
- if (fd >= 0)
- return fd;
-
- if (errno == ENOENT)
- ereport(ERROR,
- (errcode_for_file_access(),
- errmsg("requested WAL segment %s has already been removed",
- path)));
- else
- ereport(ERROR,
- (errcode_for_file_access(),
- errmsg("could not open file \"%s\": %m",
- path)));
-
- return -1; /* keep compiler quiet */
+ state->seg.ws_file = BasicOpenFile(path, O_RDONLY | PG_BINARY);
+ if (state->seg.ws_file < 0)
+ {
+ if (errno == ENOENT)
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("requested WAL segment %s has already been removed",
+ path)));
+ else
+ ereport(ERROR,
+ (errcode_for_file_access(),
+ errmsg("could not open file \"%s\": %m",
+ path)));
+ }
}
/* stock XLogReaderRoutine->segment_close callback */
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index ed8c08cb6a..b9f029d44f 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -248,7 +248,7 @@ static void LagTrackerWrite(XLogRecPtr lsn, TimestampTz local_flush_time);
static TimeOffset LagTrackerRead(int head, XLogRecPtr lsn, TimestampTz now);
static bool TransactionIdInRecentPast(TransactionId xid, uint32 epoch);
-static int WalSndSegmentOpen(XLogReaderState *state, XLogSegNo nextSegNo,
+static void WalSndSegmentOpen(XLogReaderState *state, XLogSegNo nextSegNo,
WALSegmentContext *segcxt, TimeLineID *tli_p);
static void UpdateSpillStats(LogicalDecodingContext *ctx);
@@ -2445,13 +2445,12 @@ WalSndKill(int code, Datum arg)
}
/* XLogReaderRoutine->segment_open callback */
-static int
+static void
WalSndSegmentOpen(XLogReaderState *state,
XLogSegNo nextSegNo, WALSegmentContext *segcxt,
TimeLineID *tli_p)
{
char path[MAXPGPATH];
- int fd;
/*-------
* When reading from a historic timeline, and there is a timeline switch
@@ -2488,9 +2487,9 @@ WalSndSegmentOpen(XLogReaderState *state,
}
XLogFilePath(path, *tli_p, nextSegNo, segcxt->ws_segsize);
- fd = BasicOpenFile(path, O_RDONLY | PG_BINARY);
- if (fd >= 0)
- return fd;
+ state->seg.ws_file = BasicOpenFile(path, O_RDONLY | PG_BINARY);
+ if (state->seg.ws_file >= 0)
+ return;
/*
* If the file is not found, assume it's because the standby asked for a
@@ -2513,7 +2512,6 @@ WalSndSegmentOpen(XLogReaderState *state,
(errcode_for_file_access(),
errmsg("could not open file \"%s\": %m",
path)));
- return -1; /* keep compiler quiet */
}
/*
diff --git a/src/bin/pg_waldump/pg_waldump.c b/src/bin/pg_waldump/pg_waldump.c
index 46734914b7..1a5c5a157c 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -280,7 +280,7 @@ identify_target_directory(char *directory, char *fname)
}
/* pg_waldump's XLogReaderRoutine->segment_open callback */
-static int
+static void
WALDumpOpenSegment(XLogReaderState *state,
XLogSegNo nextSegNo, WALSegmentContext *segcxt,
TimeLineID *tli_p)
@@ -300,9 +300,9 @@ WALDumpOpenSegment(XLogReaderState *state,
*/
for (tries = 0; tries < 10; tries++)
{
- fd = open_file_in_directory(segcxt->ws_dir, fname);
- if (fd >= 0)
- return fd;
+ state->seg.ws_file = open_file_in_directory(segcxt->ws_dir, fname);
+ if (state->seg.ws_file >= 0)
+ return;
if (errno == ENOENT)
{
int save_errno = errno;
@@ -318,7 +318,6 @@ WALDumpOpenSegment(XLogReaderState *state,
}
fatal_error("could not find file \"%s\": %m", fname);
- return -1; /* keep compiler quiet */
}
/*
diff --git a/src/include/access/xlogreader.h b/src/include/access/xlogreader.h
index e77f478d68..b73df02218 100644
--- a/src/include/access/xlogreader.h
+++ b/src/include/access/xlogreader.h
@@ -63,10 +63,10 @@ typedef int (*XLogPageReadCB) (XLogReaderState *xlogreader,
int reqLen,
XLogRecPtr targetRecPtr,
char *readBuf);
-typedef int (*WALSegmentOpenCB) (XLogReaderState *xlogreader,
- XLogSegNo nextSegNo,
- WALSegmentContext *segcxt,
- TimeLineID *tli_p);
+typedef void (*WALSegmentOpenCB) (XLogReaderState *xlogreader,
+ XLogSegNo nextSegNo,
+ WALSegmentContext *segcxt,
+ TimeLineID *tli_p);
typedef void (*WALSegmentCloseCB) (XLogReaderState *xlogreader);
typedef struct XLogReaderRoutine
@@ -94,8 +94,8 @@ typedef struct XLogReaderRoutine
XLogPageReadCB page_read;
/*
- * Callback to open the specified WAL segment for reading. The file
- * descriptor of the opened segment shall be returned. In case of
+ * Callback to open the specified WAL segment for reading. ->seg.ws_file
+ * shall be set to the file descriptor of the opened segment. In case of
* failure, an error shall be raised by the callback and it shall not
* return.
*
diff --git a/src/include/access/xlogutils.h b/src/include/access/xlogutils.h
index 68ce815476..b7bdc5db34 100644
--- a/src/include/access/xlogutils.h
+++ b/src/include/access/xlogutils.h
@@ -50,7 +50,7 @@ extern void FreeFakeRelcacheEntry(Relation fakerel);
extern int read_local_xlog_page(XLogReaderState *state,
XLogRecPtr targetPagePtr, int reqLen,
XLogRecPtr targetRecPtr, char *cur_page);
-extern int wal_segment_open(XLogReaderState *state,
+extern void wal_segment_open(XLogReaderState *state,
XLogSegNo nextSegNo,
WALSegmentContext *segcxt,
TimeLineID *tli_p);
--
2.20.1
