postgres.git / summary / log / commit / refs

commit    1861b20cd63ba3a2e9d547858fc4e05d882531c7
Author:   Alvaro Herrera <alvherre@alvh.no-ip.org>
Date:     Tue Sep 05 14:59:39 2017 +0000
First released in: 11.0, 10.0

    Correct base backup throttling
    
    Throttling for sending a base backup in walsender is broken for the case
    where there is a lot of WAL traffic, because the latch used to put the
    walsender to sleep is also signalled by regular WAL traffic (and each
    signal causes an additional batch of data to be sent); the net effect is
    that there is no or little actual throttling.  This is undesirable, so
    rewrite the sleep into a loop to achieve the desired effeect.
    
    Author: Jeff Janes, small tweaks by me
    Reviewed-by: Antonin Houska
    Discussion: https://postgr.es/m/CAMkU=1xH6mde-yL-Eo1TKBGNd0PB1-TMxvrNvqcAkN-qr2E9mw@mail.gmail.com


 src/backend/replication/basebackup.c | 37 +++++++++++++++++++++++++-----------
 1 file changed, 26 insertions(+), 11 deletions(-)

diff --git a/src/backend/replication/basebackup.c b/src/backend/replication/basebackup.c
index 9776858f032..12a16bd773d 100644
--- a/src/backend/replication/basebackup.c
+++ b/src/backend/replication/basebackup.c
@@ -1336,10 +1336,7 @@ _tarWriteDir(const char *pathbuf, int basepathlen, struct stat *statbuf,
 static void
 throttle(size_t increment)
 {
-	TimeOffset	elapsed,
-				elapsed_min,
-				sleep;
-	int			wait_result;
+	TimeOffset	elapsed_min;
 
 	if (throttling_counter < 0)
 		return;
@@ -1348,14 +1345,28 @@ throttle(size_t increment)
 	if (throttling_counter < throttling_sample)
 		return;
 
-	/* Time elapsed since the last measurement (and possible wake up). */
-	elapsed = GetCurrentTimestamp() - throttled_last;
-	/* How much should have elapsed at minimum? */
-	elapsed_min = elapsed_min_unit * (throttling_counter / throttling_sample);
-	sleep = elapsed_min - elapsed;
-	/* Only sleep if the transfer is faster than it should be. */
-	if (sleep > 0)
+	/* How much time should have elapsed at minimum? */
+	elapsed_min = elapsed_min_unit *
+		(throttling_counter / throttling_sample);
+
+	/*
+	 * Since the latch could be set repeatedly because of concurrently WAL
+	 * activity, sleep in a loop to ensure enough time has passed.
+	 */
+	for (;;)
 	{
+		TimeOffset	elapsed,
+					sleep;
+		int			wait_result;
+
+		/* Time elapsed since the last measurement (and possible wake up). */
+		elapsed = GetCurrentTimestamp() - throttled_last;
+
+		/* sleep if the transfer is faster than it should be */
+		sleep = elapsed_min - elapsed;
+		if (sleep <= 0)
+			break;
+
 		ResetLatch(MyLatch);
 
 		/* We're eating a potentially set latch, so check for interrupts */
@@ -1372,6 +1383,10 @@ throttle(size_t increment)
 
 		if (wait_result & WL_LATCH_SET)
 			CHECK_FOR_INTERRUPTS();
+
+		/* Done waiting? */
+		if (wait_result & WL_TIMEOUT)
+			break;
 	}
 
 	/*


[parent: a1af1e7cfaef]