Hello
Per discussion in thread [1], I propose the following patch to give
another adjustment to the xlogreader API. This results in a small but
not insignificat net reduction of lines of code. What this patch does
is adjust the signature of these new xlogreader callbacks, making the
API simpler. The changes are:
* the segment_open callback installs the FD in xlogreader state itself,
instead of passing the FD back. This was suggested by Kyotaro
Horiguchi in that thread[2].
* We no longer pass segcxt to segment_open; it's in XLogReaderState,
which is already an argument.
* We no longer pass seg/segcxt to WALRead; instead, that function takes
them from XLogReaderState, which is already an argument.
(This means XLogSendPhysical has to drink more of the fake_xlogreader
kool-aid.)
I claim the reason to do it now instead of pg14 is to make it simpler
for third-party xlogreader callers to adjust.
(Some might be thinking that I do this to avoid an API change later, but
my guts tell me that we'll adjust xlogreader again in pg14 for the
encryption stuff and other reasons, so.)
[1] https://postgr.es/m/20200406025651.fpzdb5yyb7qyh...@alap3.anarazel.de
[2]
https://postgr.es/m/20200508.114228.963995144765118400.horikyota....@gmail.com
--
Álvaro Herrera Developer, https://www.PostgreSQL.org/
diff --git a/src/backend/access/transam/xlogreader.c b/src/backend/access/transam/xlogreader.c
index 7cee8b92c9..4b6f4ada6e 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->routine.segment_open(state, nextSegNo, &tli);
+ Assert(state->seg.ws_file >= 0); /* shouldn't happen */
/* 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..0fc27215df 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -784,31 +784,28 @@ 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)
+ TimeLineID *tli_p)
{
TimeLineID tli = *tli_p;
char path[MAXPGPATH];
- 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 */
+ XLogFilePath(path, tli, nextSegNo, state->segcxt.ws_segsize);
+ 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 */
@@ -947,7 +944,6 @@ 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 9f14b99231..63e1efc778 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -248,8 +248,8 @@ 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,
- WALSegmentContext *segcxt, TimeLineID *tli_p);
+static void WalSndSegmentOpen(XLogReaderState *state, XLogSegNo nextSegNo,
+ TimeLineID *tli_p);
static void UpdateSpillStats(LogicalDecodingContext *ctx);
@@ -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);
@@ -2447,13 +2445,11 @@ WalSndKill(int code, Datum arg)
}
/* XLogReaderRoutine->segment_open callback */
-static int
-WalSndSegmentOpen(XLogReaderState *state,
- XLogSegNo nextSegNo, WALSegmentContext *segcxt,
+static void
+WalSndSegmentOpen(XLogReaderState *state, XLogSegNo nextSegNo,
TimeLineID *tli_p)
{
char path[MAXPGPATH];
- int fd;
/*-------
* When reading from a historic timeline, and there is a timeline switch
@@ -2484,15 +2480,15 @@ WalSndSegmentOpen(XLogReaderState *state,
{
XLogSegNo endSegNo;
- XLByteToSeg(sendTimeLineValidUpto, endSegNo, segcxt->ws_segsize);
+ XLByteToSeg(sendTimeLineValidUpto, endSegNo, state->segcxt.ws_segsize);
if (sendSeg->ws_segno == endSegNo)
*tli_p = sendTimeLineNextTLI;
}
- XLogFilePath(path, *tli_p, nextSegNo, segcxt->ws_segsize);
- fd = BasicOpenFile(path, O_RDONLY | PG_BINARY);
- if (fd >= 0)
- return fd;
+ XLogFilePath(path, *tli_p, nextSegNo, state->segcxt.ws_segsize);
+ 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
@@ -2515,7 +2511,6 @@ WalSndSegmentOpen(XLogReaderState *state,
(errcode_for_file_access(),
errmsg("could not open file \"%s\": %m",
path)));
- return -1; /* keep compiler quiet */
}
/*
@@ -2760,6 +2755,8 @@ 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 +2764,6 @@ 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..d1a0678935 100644
--- a/src/bin/pg_waldump/pg_waldump.c
+++ b/src/bin/pg_waldump/pg_waldump.c
@@ -280,17 +280,15 @@ identify_target_directory(char *directory, char *fname)
}
/* pg_waldump's XLogReaderRoutine->segment_open callback */
-static int
-WALDumpOpenSegment(XLogReaderState *state,
- XLogSegNo nextSegNo, WALSegmentContext *segcxt,
+static void
+WALDumpOpenSegment(XLogReaderState *state, XLogSegNo nextSegNo,
TimeLineID *tli_p)
{
TimeLineID tli = *tli_p;
char fname[MAXPGPATH];
- int fd;
int tries;
- XLogFileName(fname, tli, nextSegNo, segcxt->ws_segsize);
+ XLogFileName(fname, tli, nextSegNo, state->segcxt.ws_segsize);
/*
* In follow mode there is a short period of time after the server has
@@ -300,9 +298,9 @@ 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(state->segcxt.ws_dir, fname);
+ if (state->seg.ws_file >= 0)
+ return;
if (errno == ENOENT)
{
int save_errno = errno;
@@ -318,7 +316,6 @@ WALDumpOpenSegment(XLogReaderState *state,
}
fatal_error("could not find file \"%s\": %m", fname);
- return -1; /* keep compiler quiet */
}
/*
@@ -356,7 +353,6 @@ 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 80cf62acb7..c21b0ba972 100644
--- a/src/include/access/xlogreader.h
+++ b/src/include/access/xlogreader.h
@@ -63,10 +63,9 @@ 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,
+ TimeLineID *tli_p);
typedef void (*WALSegmentCloseCB) (XLogReaderState *xlogreader);
typedef struct XLogReaderRoutine
@@ -94,21 +93,16 @@ 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.
*
* "nextSegNo" is the number of the segment to be opened.
*
- * "segcxt" is additional information about the segment.
- *
* "tli_p" is an input/output argument. WALRead() uses it to pass the
* timeline in which the new segment should be found, but the callback can
* use it to return the TLI that it actually opened.
- *
- * BasicOpenFile() is the preferred way to open the segment file in
- * backend code, whereas open(2) should be used in frontend.
*/
WALSegmentOpenCB segment_open;
@@ -301,9 +295,7 @@ 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 */
diff --git a/src/include/access/xlogutils.h b/src/include/access/xlogutils.h
index 68ce815476..e59b6cf3a9 100644
--- a/src/include/access/xlogutils.h
+++ b/src/include/access/xlogutils.h
@@ -50,9 +50,8 @@ 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);
extern void wal_segment_close(XLogReaderState *state);
