From ebd346caf41b8e8738a49d96797ceccd04bb04dc Mon Sep 17 00:00:00 2001 From: Alvaro Herrera Date: Tue, 5 Sep 2017 16:59:39 +0200 Subject: [PATCH] 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 9776858f03..12a16bd773 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; } /*