Be clear about whether a recovery pause has taken effect.

Previously, the code and documentation seem to have essentially
assumed than a call to pg_wal_replay_pause() would take place
immediately, but that's not the case, because we only check for a
pause in certain places. This means that a tool that uses this
function and then wants to do something else afterward that is
dependent on the pause having taken effect doesn't know how long it
needs to wait to be sure that no more WAL is going to be replayed.

To avoid that, add a new function pg_get_wal_replay_pause_state()
which returns either 'not paused', 'paused requested', or 'paused'.
After calling pg_wal_replay_pause() the status will immediate change
from 'not paused' to 'pause requested'; when the startup process
has noticed this, the status will change to 'pause'.  For backward
compatibility, pg_is_wal_replay_paused() still exists and returns
the same thing as before: true if a pause has been requested,
whether or not it has taken effect yet; and false if not.
The documentation is updated to clarify.

To improve the changes that a pause request is quickly confirmed
effective, adjust things so that WaitForWALToBecomeAvailable will
swiftly reach a call to recoveryPausesHere() when a pause request
is made.

Dilip Kumar, reviewed by Simon Riggs, Kyotaro Horiguchi, Yugo Nagata,
Masahiko Sawada, and Bharath Rupireddy.

Discussion: http://postgr.es/m/CAFiTN-vcLLWEm8Zr%3DYK83rgYrT9pbC8VJCfa1kY9vL3AUPfu6g%40mail.gmail.com

1 files changed, 9 insertions, 1 deletions

diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 1e53d9d4ca6..6d384d3ce6d 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -175,6 +175,14 @@ typedef enum RecoveryState
 	RECOVERY_STATE_DONE			/* currently in production */
 } RecoveryState;
 
+/* Recovery pause states */
+typedef enum RecoveryPauseState
+{
+	RECOVERY_NOT_PAUSED,		/* pause not requested */
+	RECOVERY_PAUSE_REQUESTED,	/* pause requested, but not yet paused */
+	RECOVERY_PAUSED				/* recovery is paused */
+} RecoveryPauseState;
+
 extern PGDLLIMPORT int wal_level;
 
 /* Is WAL archiving enabled (always or only while server is running normally)? */
@@ -311,7 +319,7 @@ extern void GetXLogReceiptTime(TimestampTz *rtime, bool *fromStream);
 extern XLogRecPtr GetXLogReplayRecPtr(TimeLineID *replayTLI);
 extern XLogRecPtr GetXLogInsertRecPtr(void);
 extern XLogRecPtr GetXLogWriteRecPtr(void);
-extern bool RecoveryIsPaused(void);
+extern RecoveryPauseState GetRecoveryPauseState(void);
 extern void SetRecoveryPause(bool recoveryPause);
 extern TimestampTz GetLatestXTime(void);
 extern TimestampTz GetCurrentChunkReplayStartTime(void);