On 16 November 2016 at 12:44, Craig Ringer <cr...@2ndquadrant.com> wrote:
> Despite that, I've attached a revised version of the current approach
> incorporating fixes for the issues you mentioned. It's preceded by the
> patch to add an --endpos option to pg_recvlogical so that we can
> properly test the walsender interface too.
I didn't rebase the patch that made the timeline following tests use
the recvlogical support in PostgreNode.pm. Now attached.
Even if timeline following isn't accepted as-is, I'd greatly
appreciate inclusion of the first two patches as they add basic
coverage of pg_recvlogical and a helper to make using it in tests
simple and reliable.
--
Craig Ringer http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services
From b1266ad1adba8619bf43d4297d1ed6392e302198 Mon Sep 17 00:00:00 2001
From: Craig Ringer <cr...@2ndquadrant.com>
Date: Thu, 1 Sep 2016 12:37:40 +0800
Subject: [PATCH 1/3] Add an optional --endpos LSN argument to pg_recvlogical
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
pg_recvlogical usually just runs until cancelled or until the upstream
server disconnects. For some purposes, especially testing, it's useful
to have the ability to stop receive at a specified LSN without having
to parse the output and deal with buffering issues, etc.
Add a --endpos parameter that takes the LSN at which no further
messages should be written and receive should stop.
Craig Ringer, Álvaro Herrera
---
doc/src/sgml/ref/pg_recvlogical.sgml | 34 ++++++++
src/bin/pg_basebackup/pg_recvlogical.c | 145 +++++++++++++++++++++++++++++----
2 files changed, 164 insertions(+), 15 deletions(-)
diff --git a/doc/src/sgml/ref/pg_recvlogical.sgml b/doc/src/sgml/ref/pg_recvlogical.sgml
index b35881f..d066ce8 100644
--- a/doc/src/sgml/ref/pg_recvlogical.sgml
+++ b/doc/src/sgml/ref/pg_recvlogical.sgml
@@ -38,6 +38,14 @@ PostgreSQL documentation
constraints as <xref linkend="app-pgreceivexlog">, plus those for logical
replication (see <xref linkend="logicaldecoding">).
</para>
+
+ <para>
+ <command>pg_recvlogical</> has no equivalent to the logical decoding
+ SQL interface's peek and get modes. It sends replay confirmations for
+ data lazily as it receives it and on clean exit. To examine pending data on
+ a slot without consuming it, use
+ <link linkend="functions-replication"><function>pg_logical_slot_peek_changes</></>.
+ </para>
</refsect1>
<refsect1>
@@ -155,6 +163,32 @@ PostgreSQL documentation
</varlistentry>
<varlistentry>
+ <term><option>-E <replaceable>lsn</replaceable></option></term>
+ <term><option>--endpos=<replaceable>lsn</replaceable></option></term>
+ <listitem>
+ <para>
+ In <option>--start</option> mode, automatically stop replication
+ and exit with normal exit status 0 when receiving reaches the
+ specified LSN. If specified when not in <option>--start</option>
+ mode, an error is raised.
+ </para>
+
+ <para>
+ If there's a record with LSN exactly equal to <replaceable>lsn</>,
+ the record will be output.
+ </para>
+
+ <para>
+ The <option>--endpos</option> option is not aware of transaction
+ boundaries and may truncate output partway through a transaction.
+ Any partially output transaction will not be consumed and will be
+ replayed again when the slot is next read from. Individual messages
+ are never truncated.
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry>
<term><option>--if-not-exists</option></term>
<listitem>
<para>
diff --git a/src/bin/pg_basebackup/pg_recvlogical.c b/src/bin/pg_basebackup/pg_recvlogical.c
index cb5f989..c700edf 100644
--- a/src/bin/pg_basebackup/pg_recvlogical.c
+++ b/src/bin/pg_basebackup/pg_recvlogical.c
@@ -40,6 +40,7 @@ static int noloop = 0;
static int standby_message_timeout = 10 * 1000; /* 10 sec = default */
static int fsync_interval = 10 * 1000; /* 10 sec = default */
static XLogRecPtr startpos = InvalidXLogRecPtr;
+static XLogRecPtr endpos = InvalidXLogRecPtr;
static bool do_create_slot = false;
static bool slot_exists_ok = false;
static bool do_start_slot = false;
@@ -63,6 +64,9 @@ static XLogRecPtr output_fsync_lsn = InvalidXLogRecPtr;
static void usage(void);
static void StreamLogicalLog(void);
static void disconnect_and_exit(int code);
+static bool flushAndSendFeedback(PGconn *conn, TimestampTz *now);
+static void prepareToTerminate(PGconn *conn, XLogRecPtr endpos,
+ bool keepalive, XLogRecPtr lsn);
static void
usage(void)
@@ -81,6 +85,7 @@ usage(void)
" time between fsyncs to the output file (default: %d)\n"), (fsync_interval / 1000));
printf(_(" --if-not-exists do not error if slot already exists when creating a slot\n"));
printf(_(" -I, --startpos=LSN where in an existing slot should the streaming start\n"));
+ printf(_(" -E, --endpos=LSN exit after receiving the specified LSN\n"));
printf(_(" -n, --no-loop do not loop on connection lost\n"));
printf(_(" -o, --option=NAME[=VALUE]\n"
" pass option NAME with optional value VALUE to the\n"
@@ -281,6 +286,7 @@ StreamLogicalLog(void)
int bytes_written;
int64 now;
int hdr_len;
+ XLogRecPtr cur_record_lsn = InvalidXLogRecPtr;
if (copybuf != NULL)
{
@@ -454,6 +460,7 @@ StreamLogicalLog(void)
int pos;
bool replyRequested;
XLogRecPtr walEnd;
+ bool endposReached = false;
/*
* Parse the keepalive message, enclosed in the CopyData message.
@@ -476,18 +483,32 @@ StreamLogicalLog(void)
}
replyRequested = copybuf[pos];
- /* If the server requested an immediate reply, send one. */
- if (replyRequested)
+ if (endpos != InvalidXLogRecPtr && walEnd >= endpos)
{
- /* fsync data, so we send a recent flush pointer */
- if (!OutputFsync(now))
- goto error;
+ /*
+ * If there's nothing to read on the socket until a keepalive
+ * we know that the server has nothing to send us; and if
+ * walEnd has passed endpos, we know nothing else can have
+ * committed before endpos. So we can bail out now.
+ */
+ endposReached = true;
+ }
- now = feGetCurrentTimestamp();
- if (!sendFeedback(conn, now, true, false))
+ /* Send a reply, if necessary */
+ if (replyRequested || endposReached)
+ {
+ if (!flushAndSendFeedback(conn, &now))
goto error;
last_status = now;
}
+
+ if (endposReached)
+ {
+ prepareToTerminate(conn, endpos, true, InvalidXLogRecPtr);
+ time_to_abort = true;
+ break;
+ }
+
continue;
}
else if (copybuf[0] != 'w')
@@ -497,7 +518,6 @@ StreamLogicalLog(void)
goto error;
}
-
/*
* Read the header of the XLogData message, enclosed in the CopyData
* message. We only need the WAL location field (dataStart), the rest
@@ -515,12 +535,23 @@ StreamLogicalLog(void)
}
/* Extract WAL location for this block */
- {
- XLogRecPtr temp = fe_recvint64(©buf[1]);
+ cur_record_lsn = fe_recvint64(©buf[1]);
- output_written_lsn = Max(temp, output_written_lsn);
+ if (endpos != InvalidXLogRecPtr && cur_record_lsn > endpos)
+ {
+ /*
+ * We've read past our endpoint, so prepare to go away being
+ * cautious about what happens to our output data.
+ */
+ if (!flushAndSendFeedback(conn, &now))
+ goto error;
+ prepareToTerminate(conn, endpos, false, cur_record_lsn);
+ time_to_abort = true;
+ break;
}
+ output_written_lsn = Max(cur_record_lsn, output_written_lsn);
+
bytes_left = r - hdr_len;
bytes_written = 0;
@@ -557,10 +588,29 @@ StreamLogicalLog(void)
strerror(errno));
goto error;
}
+
+ if (endpos != InvalidXLogRecPtr && cur_record_lsn == endpos)
+ {
+ /* endpos was exactly the record we just processed, we're done */
+ if (!flushAndSendFeedback(conn, &now))
+ goto error;
+ prepareToTerminate(conn, endpos, false, cur_record_lsn);
+ time_to_abort = true;
+ break;
+ }
}
res = PQgetResult(conn);
- if (PQresultStatus(res) != PGRES_COMMAND_OK)
+ if (PQresultStatus(res) == PGRES_COPY_OUT)
+ {
+ /*
+ * We're doing a client-initiated clean exit and have sent CopyDone to
+ * the server. We've already sent replay confirmation and fsync'd so
+ * we can just clean up the connection now.
+ */
+ goto error;
+ }
+ else if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr,
_("%s: unexpected termination of replication stream: %s"),
@@ -638,6 +688,7 @@ main(int argc, char **argv)
{"password", no_argument, NULL, 'W'},
/* replication options */
{"startpos", required_argument, NULL, 'I'},
+ {"endpos", required_argument, NULL, 'E'},
{"option", required_argument, NULL, 'o'},
{"plugin", required_argument, NULL, 'P'},
{"status-interval", required_argument, NULL, 's'},
@@ -673,7 +724,7 @@ main(int argc, char **argv)
}
}
- while ((c = getopt_long(argc, argv, "f:F:nvd:h:p:U:wWI:o:P:s:S:",
+ while ((c = getopt_long(argc, argv, "f:F:nvd:h:p:U:wWI:E:o:P:s:S:",
long_options, &option_index)) != -1)
{
switch (c)
@@ -733,6 +784,16 @@ main(int argc, char **argv)
}
startpos = ((uint64) hi) << 32 | lo;
break;
+ case 'E':
+ if (sscanf(optarg, "%X/%X", &hi, &lo) != 2)
+ {
+ fprintf(stderr,
+ _("%s: could not parse end position \"%s\"\n"),
+ progname, optarg);
+ exit(1);
+ }
+ endpos = ((uint64) hi) << 32 | lo;
+ break;
case 'o':
{
char *data = pg_strdup(optarg);
@@ -857,6 +918,16 @@ main(int argc, char **argv)
exit(1);
}
+ if (endpos != InvalidXLogRecPtr && !do_start_slot)
+ {
+ fprintf(stderr,
+ _("%s: cannot use --create-slot or --drop-slot together with --endpos\n"),
+ progname);
+ fprintf(stderr, _("Try \"%s --help\" for more information.\n"),
+ progname);
+ exit(1);
+ }
+
#ifndef WIN32
pqsignal(SIGINT, sigint_handler);
pqsignal(SIGHUP, sighup_handler);
@@ -923,8 +994,8 @@ main(int argc, char **argv)
if (time_to_abort)
{
/*
- * We've been Ctrl-C'ed. That's not an error, so exit without an
- * errorcode.
+ * We've been Ctrl-C'ed or reached an exit limit condition. That's
+ * not an error, so exit without an errorcode.
*/
disconnect_and_exit(0);
}
@@ -943,3 +1014,47 @@ main(int argc, char **argv)
}
}
}
+
+/*
+ * Fsync our output data, and send a feedback message to the server. Returns
+ * true if successful, false otherwise.
+ *
+ * If successful, *now is updated to the current timestamp just before sending
+ * feedback.
+ */
+static bool
+flushAndSendFeedback(PGconn *conn, TimestampTz *now)
+{
+ /* flush data to disk, so that we send a recent flush pointer */
+ if (!OutputFsync(*now))
+ return false;
+ *now = feGetCurrentTimestamp();
+ if (!sendFeedback(conn, *now, true, false))
+ return false;
+
+ return true;
+}
+
+/*
+ * Try to inform the server about of upcoming demise, but don't wait around or
+ * retry on failure.
+ */
+static void
+prepareToTerminate(PGconn *conn, XLogRecPtr endpos, bool keepalive, XLogRecPtr lsn)
+{
+ (void) PQputCopyEnd(conn, NULL);
+ (void) PQflush(conn);
+
+ if (verbose)
+ {
+ if (keepalive)
+ fprintf(stderr, "%s: endpos %X/%X reached by keepalive\n",
+ progname,
+ (uint32) (endpos >> 32), (uint32) endpos);
+ else
+ fprintf(stderr, "%s: endpos %X/%X reached by record at %X/%X\n",
+ progname, (uint32) (endpos >> 32), (uint32) (endpos),
+ (uint32) (lsn >> 32), (uint32) lsn);
+
+ }
+}
--
2.5.5
From 8a4b4788940e2b72383e2e0195e7df7f1cf4061c Mon Sep 17 00:00:00 2001
From: Craig Ringer <cr...@2ndquadrant.com>
Date: Tue, 15 Nov 2016 16:06:16 +0800
Subject: [PATCH 2/3] Add a pg_recvlogical wrapper to PostgresNode
---
src/test/perl/PostgresNode.pm | 75 ++++++++++++++++++++++++++++-
src/test/recovery/t/006_logical_decoding.pl | 31 +++++++++++-
2 files changed, 104 insertions(+), 2 deletions(-)
diff --git a/src/test/perl/PostgresNode.pm b/src/test/perl/PostgresNode.pm
index c1b16ca..b2e4813 100644
--- a/src/test/perl/PostgresNode.pm
+++ b/src/test/perl/PostgresNode.pm
@@ -1125,7 +1125,7 @@ sub psql
# IPC::Run::run threw an exception. re-throw unless it's a
# timeout, which we'll handle by testing is_expired
die $exc_save
- if (blessed($exc_save) || $exc_save ne $timeout_exception);
+ if (blessed($exc_save) || $exc_save !~ qr/$timeout_exception/);
$ret = undef;
@@ -1325,6 +1325,79 @@ sub run_log
TestLib::run_log(@_);
}
+=pod $node->pg_recvlogical_upto(self, dbname, slot_name, endpos, timeout_secs, ...)
+
+Invoke pg_recvlogical to read from slot_name on dbname until LSN endpos, which
+corresponds to pg_recvlogical --endpos. Gives up after timeout (if nonzero).
+
+Disallows pg_recvlogial from internally retrying on error by passing --no-loop.
+
+Plugin options are passed as additional keyword arguments.
+
+If called in scalar context, returns stdout, and die()s on timeout or nonzero return.
+
+If called in array context, returns a tuple of (retval, stdout, stderr, timeout).
+timeout is the IPC::Run::Timeout object whose is_expired method can be tested
+to check for timeout. retval is undef on timeout.
+
+=cut
+
+sub pg_recvlogical_upto
+{
+ my ($self, $dbname, $slot_name, $endpos, $timeout_secs, %plugin_options) = @_;
+ my ($stdout, $stderr);
+
+ my $timeout_exception = 'pg_recvlogical timed out';
+
+ my @cmd = ('pg_recvlogical', '-S', $slot_name, '--dbname', $self->connstr($dbname));
+ push @cmd, '--endpos', $endpos if ($endpos);
+ push @cmd, '-f', '-', '--no-loop', '--start';
+
+ while (my ($k, $v) = each %plugin_options)
+ {
+ die "= is not permitted to appear in replication option name" if ($k =~ qr/=/);
+ push @cmd, "-o", "$k=$v";
+ }
+
+ my $timeout;
+ $timeout = IPC::Run::timeout($timeout_secs, exception => $timeout_exception ) if $timeout_secs;
+ my $ret = 0;
+
+ do {
+ local $@;
+ eval {
+ IPC::Run::run(\@cmd, ">", \$stdout, "2>", \$stderr, $timeout);
+ $ret = $?;
+ };
+ my $exc_save = $@;
+ if ($exc_save)
+ {
+ # IPC::Run::run threw an exception. re-throw unless it's a
+ # timeout, which we'll handle by testing is_expired
+ die $exc_save
+ if (blessed($exc_save) || $exc_save !~ qr/$timeout_exception/);
+
+ $ret = undef;
+
+ die "Got timeout exception '$exc_save' but timer not expired?!"
+ unless $timeout->is_expired;
+
+ die "$exc_save waiting for endpos $endpos with stdout '$stdout', stderr '$stderr'"
+ unless wantarray;
+ }
+ };
+
+ if (wantarray)
+ {
+ return ($ret, $stdout, $stderr, $timeout);
+ }
+ else
+ {
+ die "pg_recvlogical exited with code '$ret', stdout '$stdout' and stderr '$stderr'" if $ret;
+ return $stdout;
+ }
+}
+
=pod
=back
diff --git a/src/test/recovery/t/006_logical_decoding.pl b/src/test/recovery/t/006_logical_decoding.pl
index b80a9a9..d8cc8d3 100644
--- a/src/test/recovery/t/006_logical_decoding.pl
+++ b/src/test/recovery/t/006_logical_decoding.pl
@@ -1,9 +1,13 @@
# Testing of logical decoding using SQL interface and/or pg_recvlogical
+#
+# Most logical decoding tests are in contrib/test_decoding. This module
+# is for work that doesn't fit well there, like where server restarts
+# are required.
use strict;
use warnings;
use PostgresNode;
use TestLib;
-use Test::More tests => 2;
+use Test::More tests => 5;
# Initialize master node
my $node_master = get_new_node('master');
@@ -36,5 +40,30 @@ $result = $node_master->safe_psql('postgres', qq[SELECT pg_logical_slot_get_chan
chomp($result);
is($result, '', 'Decoding after fast restart repeats no rows');
+# Insert some rows and verify that we get the same results from pg_recvlogical
+# and the SQL interface.
+$node_master->safe_psql('postgres', qq[INSERT INTO decoding_test(x,y) SELECT s, s::text FROM generate_series(1,4) s;]);
+
+my $expected = q{BEGIN
+table public.decoding_test: INSERT: x[integer]:1 y[text]:'1'
+table public.decoding_test: INSERT: x[integer]:2 y[text]:'2'
+table public.decoding_test: INSERT: x[integer]:3 y[text]:'3'
+table public.decoding_test: INSERT: x[integer]:4 y[text]:'4'
+COMMIT};
+
+my $stdout_sql = $node_master->safe_psql('postgres', qq[SELECT data FROM pg_logical_slot_peek_changes('test_slot', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');]);
+is($stdout_sql, $expected, 'got expected output from SQL decoding session');
+
+my $endpos = $node_master->safe_psql('postgres', "SELECT location FROM pg_logical_slot_peek_changes('test_slot', NULL, NULL) ORDER BY location DESC LIMIT 1;");
+diag "waiting to replay $endpos";
+
+my $stdout_recv = $node_master->pg_recvlogical_upto('postgres', 'test_slot', $endpos, 10, 'include-xids' => '0', 'skip-empty-xacts' => '1');
+chomp($stdout_recv);
+is($stdout_recv, $expected, 'got same expected output from pg_recvlogical decoding session');
+
+$stdout_recv = $node_master->pg_recvlogical_upto('postgres', 'test_slot', $endpos, 10, 'include-xids' => '0', 'skip-empty-xacts' => '1');
+chomp($stdout_recv);
+is($stdout_recv, '', 'pg_recvlogical acknowledged changes, nothing pending on slot');
+
# done with the node
$node_master->stop;
--
2.5.5
From 161f99eb79573202c244b561821f56d1b3168158 Mon Sep 17 00:00:00 2001
From: Craig Ringer <cr...@2ndquadrant.com>
Date: Thu, 1 Sep 2016 10:16:55 +0800
Subject: [PATCH 3/3] Follow timeline switches in logical decoding
When decoding from a logical slot, it's necessary for xlog reading to
be able to read xlog from historical (i.e. not current) timelines.
Otherwise decoding fails after failover to a physical replica because
the oldest still-needed archives are in the historical timeline.
Supporting logical decoding timeline following is a pre-requisite for
logical decoding on physical standby servers. It also makes it
possible to promote a replica with logical slots to a master and
replay from those slots, allowing logical decoding applications to
follow physical failover.
Logical slots cannot actually be created on a replica without use of
the low-level C slot management APIs so this is mostly foundation work
for subsequent changes to enable logical decoding on standbys.
Tests are included to exercise the functionality using a cold disk-level copy
of the master that's started up as a replica with slots intact, but the
intended use of the functionality is with logical decoding on a standby.
Note that an earlier version of logical decoding timeline following
was committed to 9.5 as 24c5f1a103ce, 3a3b309041b0, 82c83b337202, and
f07d18b6e94d. It was then reverted by c1543a81a7a8 just after 9.5
feature freeze when issues were discovered too late to safely fix them
in the 9.5 release cycle.
The prior approach failed to consider that a record could be split
across pages that are on different segments, where the new segment
contains the start of a new timeline. In that case the old segment
might be missing or renamed with a .partial suffix.
This patch reworks the logic to be page-based and in the process
simplify how the last timeline for a segment is looked up.
---
src/backend/access/transam/xlogutils.c | 200 +++++++++++++++++++--
src/backend/replication/logical/logicalfuncs.c | 7 +-
src/backend/replication/walsender.c | 11 +-
src/include/access/xlogreader.h | 16 ++
src/include/access/xlogutils.h | 3 +
src/test/recovery/Makefile | 2 +
.../recovery/t/009_logical_decoding_timelines.pl | 130 ++++++++++++++
7 files changed, 347 insertions(+), 22 deletions(-)
create mode 100644 src/test/recovery/t/009_logical_decoding_timelines.pl
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c
index 51a8e8d..ab15cf3 100644
--- a/src/backend/access/transam/xlogutils.c
+++ b/src/backend/access/transam/xlogutils.c
@@ -19,6 +19,7 @@
#include <unistd.h>
+#include "access/timeline.h"
#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "access/xlogutils.h"
@@ -660,6 +661,7 @@ XLogRead(char *buf, TimeLineID tli, XLogRecPtr startptr, Size count)
/* state maintained across calls */
static int sendFile = -1;
static XLogSegNo sendSegNo = 0;
+ static TimeLineID sendTLI = 0;
static uint32 sendOff = 0;
p = buf;
@@ -675,7 +677,8 @@ XLogRead(char *buf, TimeLineID tli, XLogRecPtr startptr, Size count)
startoff = recptr % XLogSegSize;
/* Do we need to switch to a different xlog segment? */
- if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo))
+ if (sendFile < 0 || !XLByteInSeg(recptr, sendSegNo) ||
+ sendTLI != tli)
{
char path[MAXPGPATH];
@@ -702,6 +705,7 @@ XLogRead(char *buf, TimeLineID tli, XLogRecPtr startptr, Size count)
path)));
}
sendOff = 0;
+ sendTLI = tli;
}
/* Need to seek in the file? */
@@ -750,6 +754,129 @@ XLogRead(char *buf, TimeLineID tli, XLogRecPtr startptr, Size count)
}
/*
+ * Determine which timeline to read an xlog page from and set the
+ * XLogReaderState's currTLI to that timeline ID.
+ *
+ * It's necessary to care about timelines in xlogreader and logical decoding
+ * when we might be reading xlog generated prior to a promotion, either if
+ * we're currently a standby in recovery or if we're a promoted master reading
+ * xlogs generated by the old master before our promotion. Notably, logical
+ * decoding on a standby needs to be able to replay any remaining pending data
+ * from the old timeline when the standby or one of its upstreams being
+ * promoted.
+ *
+ * wantPage must be set to the start address of the page to read and
+ * wantLength to the amount of the page that will be read, up to
+ * XLOG_BLCKSZ. If the amount to be read isn't known, pass XLOG_BLCKSZ.
+ *
+ * We switch to an xlog segment from the new timeline eagerly when on a
+ * historical timeline, as soon as we reach the start of the xlog segment
+ * containing the timeline switch. The server copied the segment to the new
+ * timeline so all the data up to the switch point is the same, but there's no
+ * guarantee the old segment will still exist. It may have been deleted or
+ * renamed with a .partial suffix so we can't necessarily keep reading from
+ * the old TLI even though tliSwitchPoint says it's OK.
+ *
+ * We can't just check the timeline when we read a page on a different segment
+ * to the last page. We could've received a timeline switch from a cascading
+ * upstream, so the current segment ends and we have to switch to a new one.
+ * Even in the middle of reading a page we could have to dump the cached page
+ * and switch to a new TLI.
+ *
+ * Because of this, callers MAY NOT assume that currTLI is the timeline that
+ * will be in a page's xlp_tli; the page may begin on an older timeline or we
+ * might be reading from historical timeline data on a segment that's been
+ * copied to a new timeline.
+ *
+ * The caller must also make sure it doesn't read past the current replay
+ * position if executing in recovery, so it doesn't fail to notice that the
+ * current timeline became historical.
+ */
+void
+XLogReadDetermineTimeline(XLogReaderState *state, XLogRecPtr wantPage, uint32 wantLength)
+{
+ const XLogRecPtr lastReadPage = state->readSegNo * XLogSegSize + state->readOff;
+
+ Assert(wantPage != InvalidXLogRecPtr && wantPage % XLOG_BLCKSZ == 0);
+ Assert(wantLength <= XLOG_BLCKSZ);
+ Assert(state->readLen == 0 || state->readLen <= XLOG_BLCKSZ);
+
+ /*
+ * If the desired page is currently read in and valid, we have nothing to do.
+ *
+ * The caller should've ensured that it didn't previously advance readOff
+ * past the valid limit of this timeline, so it doesn't matter if the current
+ * TLI has since become historical.
+ */
+ if (lastReadPage == wantPage &&
+ state->readLen != 0 &&
+ lastReadPage + state->readLen >= wantPage + Min(wantLength,XLOG_BLCKSZ-1))
+ return;
+
+ /*
+ * If we're reading from the current timeline, it hasn't become historical
+ * and the page we're reading is after the last page read, we can again
+ * just carry on. (Seeking backwards requires a check to make sure the older
+ * page isn't on a prior timeline).
+ */
+ if (state->currTLI == ThisTimeLineID && wantPage >= lastReadPage)
+ {
+ Assert(state->currTLIValidUntil == InvalidXLogRecPtr);
+ return;
+ }
+
+ /*
+ * If we're just reading pages from a previously validated historical
+ * timeline and the timeline we're reading from is valid until the
+ * end of the current segment we can just keep reading.
+ */
+ if (state->currTLIValidUntil != InvalidXLogRecPtr &&
+ state->currTLI != ThisTimeLineID &&
+ state->currTLI != 0 &&
+ (wantPage + wantLength) / XLogSegSize < state->currTLIValidUntil / XLogSegSize)
+ return;
+
+ /*
+ * If we reach this point we're either looking up a page for random access,
+ * the current timeline just became historical, or we're reading from a new
+ * segment containing a timeline switch. In all cases we need to determine
+ * the newest timeline on the segment.
+ *
+ * If it's the current timeline we can just keep reading from here unless
+ * we detect a timeline switch that makes the current timeline historical.
+ * If it's a historical timeline we can read all the segment on the newest
+ * timeline because it contains all the old timelines' data too. So only
+ * one switch check is required.
+ */
+ {
+ /*
+ * We need to re-read the timeline history in case it's been changed
+ * by a promotion or replay from a cascaded replica.
+ */
+ List *timelineHistory = readTimeLineHistory(ThisTimeLineID);
+
+ XLogRecPtr endOfSegment = (((wantPage / XLogSegSize) + 1) * XLogSegSize) - 1;
+
+ Assert(wantPage / XLogSegSize == endOfSegment / XLogSegSize);
+
+ /* Find the timeline of the last LSN on the segment containing wantPage. */
+ state->currTLI = tliOfPointInHistory(endOfSegment, timelineHistory);
+ state->currTLIValidUntil = tliSwitchPoint(state->currTLI, timelineHistory,
+ &state->nextTLI);
+
+ Assert(state->currTLIValidUntil == InvalidXLogRecPtr ||
+ wantPage + wantLength < state->currTLIValidUntil);
+
+ list_free_deep(timelineHistory);
+
+ elog(DEBUG3, "switched to timeline %u valid until %X/%X",
+ state->currTLI,
+ (uint32)(state->currTLIValidUntil >> 32),
+ (uint32)(state->currTLIValidUntil));
+ }
+}
+
+/*
* read_page callback for reading local xlog files
*
* Public because it would likely be very helpful for someone writing another
@@ -770,28 +897,71 @@ read_local_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr,
int count;
loc = targetPagePtr + reqLen;
+
+ /* Make sure enough xlog is available... */
while (1)
{
/*
- * TODO: we're going to have to do something more intelligent about
- * timelines on standbys. Use readTimeLineHistory() and
- * tliOfPointInHistory() to get the proper LSN? For now we'll catch
- * that case earlier, but the code and TODO is left in here for when
- * that changes.
+ * Check which timeline to get the record from.
+ *
+ * We have to do it each time through the loop because if we're in
+ * recovery as a cascading standby, the current timeline might've
+ * become historical. We can't rely on RecoveryInProgress() because
+ * in a standby configuration like
+ *
+ * A => B => C
+ *
+ * if we're a logical decoding on C, and B gets promoted, our timeline
+ * will change while we remain in recovery.
*/
- if (!RecoveryInProgress())
+ XLogReadDetermineTimeline(state, targetPagePtr, reqLen);
+
+ if (state->currTLI == ThisTimeLineID)
{
- *pageTLI = ThisTimeLineID;
- read_upto = GetFlushRecPtr();
+ /*
+ * We're reading from the current timeline so we might have to
+ * wait for the desired record to be generated (or, for a standby,
+ * received & replayed)
+ */
+ if (!RecoveryInProgress())
+ {
+ *pageTLI = ThisTimeLineID;
+ read_upto = GetFlushRecPtr();
+ }
+ else
+ read_upto = GetXLogReplayRecPtr(pageTLI);
+
+ if (loc <= read_upto)
+ break;
+
+ CHECK_FOR_INTERRUPTS();
+ pg_usleep(1000L);
}
else
- read_upto = GetXLogReplayRecPtr(pageTLI);
-
- if (loc <= read_upto)
+ {
+ /*
+ * We're on a historical timeline, so limit reading to the switch
+ * point where we moved to the next timeline.
+ *
+ * We don't need to GetFlushRecPtr or GetXLogReplayRecPtr. We know
+ * about the new timeline, so we must've received past the end of
+ * it.
+ */
+ read_upto = state->currTLIValidUntil;
+
+ /*
+ * Setting pageTLI to our wanted record's TLI is slightly wrong;
+ * the page might begin on an older timeline if it contains a
+ * timeline switch, since its xlog segment will have been copied
+ * from the prior timeline. This is pretty harmless though, as
+ * nothing cares so long as the timeline doesn't go backwards. We
+ * should read the page header instead; FIXME someday.
+ */
+ *pageTLI = state->currTLI;
+
+ /* No need to wait on a historical timeline */
break;
-
- CHECK_FOR_INTERRUPTS();
- pg_usleep(1000L);
+ }
}
if (targetPagePtr + XLOG_BLCKSZ <= read_upto)
diff --git a/src/backend/replication/logical/logicalfuncs.c b/src/backend/replication/logical/logicalfuncs.c
index 318726e..a8f7b76 100644
--- a/src/backend/replication/logical/logicalfuncs.c
+++ b/src/backend/replication/logical/logicalfuncs.c
@@ -234,13 +234,13 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
rsinfo->setResult = p->tupstore;
rsinfo->setDesc = p->tupdesc;
+ ReplicationSlotAcquire(NameStr(*name));
+
/* compute the current end-of-wal */
if (!RecoveryInProgress())
end_of_wal = GetFlushRecPtr();
else
- end_of_wal = GetXLogReplayRecPtr(NULL);
-
- ReplicationSlotAcquire(NameStr(*name));
+ end_of_wal = GetXLogReplayRecPtr(&ThisTimeLineID);
PG_TRY();
{
@@ -279,6 +279,7 @@ pg_logical_slot_get_changes_guts(FunctionCallInfo fcinfo, bool confirm, bool bin
/* invalidate non-timetravel entries */
InvalidateSystemCaches();
+ /* Decode until we run out of records */
while ((startptr != InvalidXLogRecPtr && startptr < end_of_wal) ||
(ctx->reader->EndRecPtr != InvalidXLogRecPtr && ctx->reader->EndRecPtr < end_of_wal))
{
diff --git a/src/backend/replication/walsender.c b/src/backend/replication/walsender.c
index bc5e508..ef8ba80 100644
--- a/src/backend/replication/walsender.c
+++ b/src/backend/replication/walsender.c
@@ -47,6 +47,7 @@
#include "access/transam.h"
#include "access/xact.h"
#include "access/xlog_internal.h"
+#include "access/xlogutils.h"
#include "catalog/pg_type.h"
#include "commands/dbcommands.h"
@@ -756,6 +757,12 @@ logical_read_xlog_page(XLogReaderState *state, XLogRecPtr targetPagePtr, int req
XLogRecPtr flushptr;
int count;
+ XLogReadDetermineTimeline(state, targetPagePtr, reqLen);
+ sendTimeLineIsHistoric = state->currTLI == ThisTimeLineID;
+ sendTimeLine = state->currTLI;
+ sendTimeLineValidUpto = state->currTLIValidUntil;
+ sendTimeLineNextTLI = state->nextTLI;
+
/* make sure we have enough WAL available */
flushptr = WalSndWaitForWal(targetPagePtr + reqLen);
@@ -984,10 +991,6 @@ StartLogicalReplication(StartReplicationCmd *cmd)
pq_endmessage(&buf);
pq_flush();
- /* setup state for XLogReadPage */
- sendTimeLineIsHistoric = false;
- sendTimeLine = ThisTimeLineID;
-
/*
* Initialize position to the last ack'ed one, then the xlog records begin
* to be shipped from that position.
diff --git a/src/include/access/xlogreader.h b/src/include/access/xlogreader.h
index deaa7f5..8f96728 100644
--- a/src/include/access/xlogreader.h
+++ b/src/include/access/xlogreader.h
@@ -160,6 +160,22 @@ struct XLogReaderState
/* beginning of the WAL record being read. */
XLogRecPtr currRecPtr;
+ /* timeline to read it from, 0 if a lookup is required */
+ TimeLineID currTLI;
+ /*
+ * Safe point to read to in currTLI if current TLI is historical
+ * (tliSwitchPoint) or InvalidXLogRecPtr if on current timeline.
+ *
+ * Actually set to the start of the segment containing the timeline
+ * switch that ends currTLI's validity, not the LSN of the switch
+ * its self, since we can't assume the old segment will be present.
+ */
+ XLogRecPtr currTLIValidUntil;
+ /*
+ * If currTLI is not the most recent known timeline, the next timeline to
+ * read from when currTLIValidUntil is reached.
+ */
+ TimeLineID nextTLI;
/* Buffer for current ReadRecord result (expandable) */
char *readRecordBuf;
diff --git a/src/include/access/xlogutils.h b/src/include/access/xlogutils.h
index d027ea1..f0ee352 100644
--- a/src/include/access/xlogutils.h
+++ b/src/include/access/xlogutils.h
@@ -52,4 +52,7 @@ extern int read_local_xlog_page(XLogReaderState *state,
XLogRecPtr targetRecPtr, char *cur_page,
TimeLineID *pageTLI);
+extern void XLogReadDetermineTimeline(XLogReaderState *state,
+ XLogRecPtr wantPage, uint32 wantLength);
+
#endif
diff --git a/src/test/recovery/Makefile b/src/test/recovery/Makefile
index a847952..d2ff1e9 100644
--- a/src/test/recovery/Makefile
+++ b/src/test/recovery/Makefile
@@ -9,6 +9,8 @@
#
#-------------------------------------------------------------------------
+EXTRA_INSTALL=contrib/test_decoding
+
subdir = src/test/recovery
top_builddir = ../../..
include $(top_builddir)/src/Makefile.global
diff --git a/src/test/recovery/t/009_logical_decoding_timelines.pl b/src/test/recovery/t/009_logical_decoding_timelines.pl
new file mode 100644
index 0000000..09830dc
--- /dev/null
+++ b/src/test/recovery/t/009_logical_decoding_timelines.pl
@@ -0,0 +1,130 @@
+# Demonstrate that logical can follow timeline switches.
+#
+# Logical replication slots can follow timeline switches but it's
+# normally not possible to have a logical slot on a replica where
+# promotion and a timeline switch can occur. The only ways
+# we can create that circumstance are:
+#
+# * By doing a filesystem-level copy of the DB, since pg_basebackup
+# excludes pg_replslot but we can copy it directly; or
+#
+# * by creating a slot directly at the C level on the replica and
+# advancing it as we go using the low level APIs. It can't be done
+# from SQL since logical decoding isn't allowed on replicas.
+#
+# This module uses the first approach to show that timeline following
+# on a logical slot works.
+#
+use strict;
+use warnings;
+
+use PostgresNode;
+use TestLib;
+use Test::More tests => 7;
+use RecursiveCopy;
+use File::Copy;
+use IPC::Run ();
+use Scalar::Util qw(blessed);
+
+my ($stdout, $stderr, $ret);
+
+# Initialize master node
+my $node_master = get_new_node('master');
+$node_master->init(allows_streaming => 1, has_archiving => 1);
+$node_master->append_conf('postgresql.conf', "wal_level = 'logical'\n");
+$node_master->append_conf('postgresql.conf', "max_replication_slots = 2\n");
+$node_master->append_conf('postgresql.conf', "max_wal_senders = 2\n");
+$node_master->append_conf('postgresql.conf', "log_min_messages = 'debug2'\n");
+$node_master->dump_info;
+$node_master->start;
+
+diag "Testing logical timeline following with a filesystem-level copy";
+
+$node_master->safe_psql('postgres',
+"SELECT pg_create_logical_replication_slot('before_basebackup', 'test_decoding');"
+);
+$node_master->safe_psql('postgres', "CREATE TABLE decoding(blah text);");
+$node_master->safe_psql('postgres',
+ "INSERT INTO decoding(blah) VALUES ('beforebb');");
+$node_master->safe_psql('postgres', 'CHECKPOINT;');
+
+my $backup_name = 'b1';
+$node_master->backup_fs_hot($backup_name);
+
+my $node_replica = get_new_node('replica');
+$node_replica->init_from_backup(
+ $node_master, $backup_name,
+ has_streaming => 1,
+ has_restoring => 1);
+$node_replica->start;
+
+$node_master->safe_psql('postgres',
+"SELECT pg_create_logical_replication_slot('after_basebackup', 'test_decoding');"
+);
+$node_master->safe_psql('postgres',
+ "INSERT INTO decoding(blah) VALUES ('afterbb');");
+$node_master->safe_psql('postgres', 'CHECKPOINT;');
+
+# Verify that only the before base_backup slot is on the replica
+$stdout = $node_replica->safe_psql('postgres',
+ 'SELECT slot_name FROM pg_replication_slots ORDER BY slot_name');
+is($stdout, 'before_basebackup',
+ 'Expected to find only slot before_basebackup on replica');
+
+# Boom, crash
+$node_master->stop('immediate');
+
+$node_replica->promote;
+$node_replica->poll_query_until('postgres',
+ "SELECT NOT pg_is_in_recovery();");
+
+$node_replica->safe_psql('postgres',
+ "INSERT INTO decoding(blah) VALUES ('after failover');");
+
+# Shouldn't be able to read from slot created after base backup
+($ret, $stdout, $stderr) = $node_replica->psql('postgres',
+"SELECT data FROM pg_logical_slot_peek_changes('after_basebackup', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');"
+);
+is($ret, 3, 'replaying from after_basebackup slot fails');
+like(
+ $stderr,
+ qr/replication slot "after_basebackup" does not exist/,
+ 'after_basebackup slot missing');
+
+# Should be able to read from slot created before base backup
+($ret, $stdout, $stderr) = $node_replica->psql(
+ 'postgres',
+"SELECT data FROM pg_logical_slot_peek_changes('before_basebackup', NULL, NULL, 'include-xids', '0', 'skip-empty-xacts', '1');",
+ timeout => 30);
+is($ret, 0, 'replay from slot before_basebackup succeeds');
+
+my $final_expected_output_bb = q(BEGIN
+table public.decoding: INSERT: blah[text]:'beforebb'
+COMMIT
+BEGIN
+table public.decoding: INSERT: blah[text]:'afterbb'
+COMMIT
+BEGIN
+table public.decoding: INSERT: blah[text]:'after failover'
+COMMIT);
+is($stdout, $final_expected_output_bb, 'decoded expected data from slot before_basebackup');
+is($stderr, '', 'replay from slot before_basebackup produces no stderr');
+
+# So far we've peeked the slots, so when we fetch the same info over
+# pg_recvlogical we should get complete results. First, find out the commit lsn
+# of the last transaction. There's no max(pg_lsn), so:
+
+my $endpos = $node_replica->safe_psql('postgres', "SELECT location FROM pg_logical_slot_peek_changes('before_basebackup', NULL, NULL) ORDER BY location DESC LIMIT 1;");
+
+# now use the walsender protocol to peek the slot changes and make sure we see
+# the same results.
+
+$stdout = $node_replica->pg_recvlogical_upto('postgres', 'before_basebackup',
+ $endpos, 30, 'include-xids' => '0', 'skip-empty-xacts' => '1');
+
+# walsender likes to add a newline
+chomp($stdout);
+is($stdout, $final_expected_output_bb, 'got same output from walsender via pg_recvlogical on before_basebackup');
+
+# We don't need the standby anymore
+$node_replica->teardown_node();
--
2.5.5
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