Hello,
On Wed, 24 Jul 2019 14:33:27 +0200
Jehan-Guillaume de Rorthais <j...@dalibo.com> wrote:
> On Wed, 24 Jul 2019 09:49:05 +0900
> Michael Paquier <mich...@paquier.xyz> wrote:
>
> > On Tue, Jul 23, 2019 at 06:05:18PM +0200, Jehan-Guillaume de Rorthais
> > wrote:
[...]
> > I think that there are arguments for being more flexible with it, and
> > perhaps have a system-level view to be able to look at some of its fields.
>
> Great idea. I'll give it a try to keep the discussion on.
After some thinking, I did not find enough data to expose to justify the
creation a system-level view. As I just need the current timeline I
wrote "pg_current_timeline()". Please, find the patch in attachment.
The current behavior is quite simple:
* if the cluster is in production, return ThisTimeLineID
* else return walrcv->receivedTLI (using GetWalRcvWriteRecPtr)
This is really naive implementation. We should probably add some code around
the startup process to gather and share general recovery stats. This would
allow to fetch eg. the current recovery method, latest xlog file name restored
from archives or streaming, its timeline, etc.
Any thoughts?
Regards,
>From 5b06d83e000132eca5a3173e96651ddf4531cff6 Mon Sep 17 00:00:00 2001
From: Jehan-Guillaume de Rorthais <j...@dalibo.com>
Date: Thu, 25 Jul 2019 19:36:40 +0200
Subject: [PATCH] Add function pg_current_timeline
---
src/backend/access/transam/xlog.c | 26 ++++++++++++++++++++++++++
src/backend/access/transam/xlogfuncs.c | 17 +++++++++++++++++
src/include/access/xlog.h | 1 +
src/include/catalog/pg_proc.dat | 6 ++++++
4 files changed, 50 insertions(+)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index da3d250986..9da876c0ac 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -12243,3 +12243,29 @@ XLogRequestWalReceiverReply(void)
{
doRequestWalReceiverReply = true;
}
+
+/*
+ * Returns current active timeline.
+ * During production, returns ThisTimeLineID.
+ * During standby, returns the timeline of the latest record flushed to XLOG.
+ */
+TimeLineID
+GetCurrentTimeLine(void)
+{
+ TimeLineID localTimeLineID;
+ bool localRecoveryInProgress;
+
+ SpinLockAcquire(&XLogCtl->info_lck);
+
+ localTimeLineID = XLogCtl->ThisTimeLineID;
+ localRecoveryInProgress = XLogCtl->SharedRecoveryInProgress;
+
+ SpinLockRelease(&XLogCtl->info_lck);
+
+ if (localRecoveryInProgress) {
+ GetWalRcvWriteRecPtr(NULL, &localTimeLineID);
+ return localTimeLineID;
+ }
+
+ return localTimeLineID;
+}
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index b35043bf71..c1cb9e8819 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -776,3 +776,20 @@ pg_promote(PG_FUNCTION_ARGS)
(errmsg("server did not promote within %d seconds", wait_seconds)));
PG_RETURN_BOOL(false);
}
+
+/*
+ * Returns the current timeline
+ */
+Datum
+pg_current_timeline(PG_FUNCTION_ARGS)
+{
+ TimeLineID currentTL = GetCurrentTimeLine();
+
+ /*
+ * we have no information about the timeline if the walreceiver
+ * is disabled or hasn't streamed anything yet,
+ */
+ if (!currentTL) PG_RETURN_NULL();
+
+ PG_RETURN_INT32(currentTL);
+}
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index d519252aad..f0502c0b41 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -313,6 +313,7 @@ extern XLogRecPtr GetInsertRecPtr(void);
extern XLogRecPtr GetFlushRecPtr(void);
extern XLogRecPtr GetLastImportantRecPtr(void);
extern void RemovePromoteSignalFiles(void);
+extern TimeLineID GetCurrentTimeLine(void);
extern bool CheckPromoteSignal(void);
extern void WakeupRecovery(void);
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 0902dce5f1..42cd7c3486 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -6006,6 +6006,12 @@
{ oid => '2851', descr => 'wal filename, given a wal location',
proname => 'pg_walfile_name', prorettype => 'text', proargtypes => 'pg_lsn',
prosrc => 'pg_walfile_name' },
+{ oid => '3434',
+ descr => 'return the current timeline',
+ proname => 'pg_current_timeline', prorettype => 'int4',
+ proargtypes => '', proallargtypes => '{int4}',
+ proargmodes => '{o}', proargnames => '{timeline}',
+ prosrc => 'pg_current_timeline' },
{ oid => '3165', descr => 'difference in bytes, given two wal locations',
proname => 'pg_wal_lsn_diff', prorettype => 'numeric',
--
2.20.1
