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Commit91fa853

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Attempt to fix error recovery in COPY BOTH mode.
Previously, libpq and the backend had opposite ideas about whetherit was necessary for the client to send a CopyDone message afterreceiving an ErrorResponse, making it impossible to cleanly exitCOPY BOTH mode. Fix libpq so that works correctly, adopting thebackend's notion that an ErrorResponse kills the copy in bothdirections.Adjust receivelog.c to avoid a degradation in the quality of theresulting error messages. libpqwalreceiver.c is already doingthe right thing, so no adjustment needed there.Add an explicit statement to the documentation explaining howthis part of the protocol is supposed to work, in the hopes ofavoiding future confusion in this area.Since the consequences of all this confusion are very limited,especially in the back-branches where no client ever attemptsto exit COPY BOTH mode without closing the connection entirely,no back-patch.
1 parent43e7a66 commit91fa853

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3 files changed

+51
-36
lines changed

3 files changed

+51
-36
lines changed

‎doc/src/sgml/protocol.sgml

Lines changed: 7 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -1031,8 +1031,13 @@
10311031
goes into copy-in mode, and the server may not send any more CopyData
10321032
messages. After both sides have sent a CopyDone message, the copy mode
10331033
is terminated, and the backend reverts to the command-processing mode.
1034-
See <xref linkend="protocol-replication"> for more information on the
1035-
subprotocol transmitted over copy-both mode.
1034+
In the event of a backend-detected error during copy-both mode,
1035+
the backend will issue an ErrorResponse message, discard frontend messages
1036+
until a Sync message is received, and then issue ReadyForQuery and return
1037+
to normal processing. The frontend should treat receipt of ErrorResponse
1038+
as terminating the copy in both directions; no CopyDone should be sent
1039+
in this case. See <xref linkend="protocol-replication"> for more
1040+
information on the subprotocol transmitted over copy-both mode.
10361041
</para>
10371042

10381043
<para>

‎src/bin/pg_basebackup/receivelog.c

Lines changed: 28 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -32,10 +32,10 @@
3232
staticintwalfile=-1;
3333
staticcharcurrent_walfile_name[MAXPGPATH]="";
3434

35-
staticboolHandleCopyStream(PGconn*conn,XLogRecPtrstartpos,uint32timeline,
36-
char*basedir,stream_stop_callbackstream_stop,
37-
intstandby_message_timeout,char*partial_suffix,
38-
XLogRecPtr*stoppos);
35+
staticPGresult*HandleCopyStream(PGconn*conn,XLogRecPtrstartpos,
36+
uint32timeline,char*basedir,
37+
stream_stop_callbackstream_stop,intstandby_message_timeout,
38+
char*partial_suffix,XLogRecPtr*stoppos);
3939

4040
/*
4141
* Open a new WAL file in the specified directory.
@@ -615,9 +615,10 @@ ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
615615
PQclear(res);
616616

617617
/* Stream the WAL */
618-
if (!HandleCopyStream(conn,startpos,timeline,basedir,stream_stop,
619-
standby_message_timeout,partial_suffix,
620-
&stoppos))
618+
res=HandleCopyStream(conn,startpos,timeline,basedir,stream_stop,
619+
standby_message_timeout,partial_suffix,
620+
&stoppos);
621+
if (res==NULL)
621622
gotoerror;
622623

623624
/*
@@ -630,7 +631,6 @@ ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
630631
* restart streaming from the next timeline.
631632
*/
632633

633-
res=PQgetResult(conn);
634634
if (PQresultStatus(res)==PGRES_TUPLES_OK)
635635
{
636636
/*
@@ -708,10 +708,11 @@ ReceiveXlogStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
708708
* The main loop of ReceiveXLogStream. Handles the COPY stream after
709709
* initiating streaming with the START_STREAMING command.
710710
*
711-
* If the COPY ends normally, returns true and sets *stoppos to the last
712-
* byte written. On error, returns false.
711+
* If the COPY ends (not necessarily successfully) due a message from the
712+
* server, returns a PGresult and sets sets *stoppos to the last byte written.
713+
* On any other sort of error, returns NULL.
713714
*/
714-
staticbool
715+
staticPGresult*
715716
HandleCopyStream(PGconn*conn,XLogRecPtrstartpos,uint32timeline,
716717
char*basedir,stream_stop_callbackstream_stop,
717718
intstandby_message_timeout,char*partial_suffix,
@@ -832,9 +833,12 @@ HandleCopyStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
832833
}
833834
if (r==-1)
834835
{
836+
PGresult*res=PQgetResult(conn);
837+
835838
/*
836-
* The server closed its end of the copy stream. Close ours
837-
* if we haven't done so already, and exit.
839+
* The server closed its end of the copy stream. If we haven't
840+
* closed ours already, we need to do so now, unless the server
841+
* threw an error, in which case we don't.
838842
*/
839843
if (still_sending)
840844
{
@@ -843,18 +847,23 @@ HandleCopyStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
843847
/* Error message written in close_walfile() */
844848
gotoerror;
845849
}
846-
if (PQputCopyEnd(conn,NULL) <=0||PQflush(conn))
850+
if (PQresultStatus(res)==PGRES_COPY_IN)
847851
{
848-
fprintf(stderr,_("%s: could not send copy-end packet: %s"),
849-
progname,PQerrorMessage(conn));
850-
gotoerror;
852+
if (PQputCopyEnd(conn,NULL) <=0||PQflush(conn))
853+
{
854+
fprintf(stderr,
855+
_("%s: could not send copy-end packet: %s"),
856+
progname,PQerrorMessage(conn));
857+
gotoerror;
858+
}
859+
res=PQgetResult(conn);
851860
}
852861
still_sending= false;
853862
}
854863
if (copybuf!=NULL)
855864
PQfreemem(copybuf);
856865
*stoppos=blockpos;
857-
returntrue;
866+
returnres;
858867
}
859868
if (r==-2)
860869
{
@@ -1030,5 +1039,5 @@ HandleCopyStream(PGconn *conn, XLogRecPtr startpos, uint32 timeline,
10301039
error:
10311040
if (copybuf!=NULL)
10321041
PQfreemem(copybuf);
1033-
returnfalse;
1042+
returnNULL;
10341043
}

‎src/interfaces/libpq/fe-protocol3.c

Lines changed: 16 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -1466,7 +1466,23 @@ getCopyDataMessage(PGconn *conn)
14661466
break;
14671467
case'd':/* Copy Data, pass it back to caller */
14681468
returnmsgLength;
1469+
case'c':
1470+
/*
1471+
* If this is a CopyDone message, exit COPY_OUT mode and let
1472+
* caller read status with PQgetResult(). If we're in
1473+
* COPY_BOTH mode, return to COPY_IN mode.
1474+
*/
1475+
if (conn->asyncStatus==PGASYNC_COPY_BOTH)
1476+
conn->asyncStatus=PGASYNC_COPY_IN;
1477+
else
1478+
conn->asyncStatus=PGASYNC_BUSY;
1479+
return-1;
14691480
default:/* treat as end of copy */
1481+
/*
1482+
* Any other message terminates either COPY_IN or COPY_BOTH
1483+
* mode.
1484+
*/
1485+
conn->asyncStatus=PGASYNC_BUSY;
14701486
return-1;
14711487
}
14721488

@@ -1499,22 +1515,7 @@ pqGetCopyData3(PGconn *conn, char **buffer, int async)
14991515
*/
15001516
msgLength=getCopyDataMessage(conn);
15011517
if (msgLength<0)
1502-
{
1503-
/*
1504-
* On end-of-copy, exit COPY_OUT or COPY_BOTH mode and let caller
1505-
* read status with PQgetResult().The normal case is that it's
1506-
* Copy Done, but we let parseInput read that.If error, we
1507-
* expect the state was already changed.
1508-
*/
1509-
if (msgLength==-1)
1510-
{
1511-
if (conn->asyncStatus==PGASYNC_COPY_BOTH)
1512-
conn->asyncStatus=PGASYNC_COPY_IN;
1513-
else
1514-
conn->asyncStatus=PGASYNC_BUSY;
1515-
}
15161518
returnmsgLength;/* end-of-copy or error */
1517-
}
15181519
if (msgLength==0)
15191520
{
15201521
/* Don't block if async read requested */

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