Ori.livneh has uploaded a new change for review.
https://gerrit.wikimedia.org/r/227614
Change subject: RedisBagOStuff: if no alternatives, skip master link status
check
......................................................................
RedisBagOStuff: if no alternatives, skip master link status check
If RedisBagOStuff::getConnection() is able to establish a connection, only
check the master link status if automatic failover is enabled and if there are
other viable servers left to consider. If there are no servers left to
consider, or if automatic failover is not configured, just return the
connection handle without subjecting it to further tests.
This will have the side-effect of making RedisBagOStuff compatible with
Nutcracker, which does not implement the INFO command. This is because when
MediaWiki is configured to use Nutcracker, the server pool will consist of a
single server (namely, Nutcracker itself), and thus there will be no other
server to consider, so INFO will never be executed.
Change-Id: I3812ec5a0b22df122bdf44350bc0496574c02ce8
---
M includes/objectcache/RedisBagOStuff.php
1 file changed, 29 insertions(+), 17 deletions(-)
git pull ssh://gerrit.wikimedia.org:29418/mediawiki/core
refs/changes/14/227614/1
diff --git a/includes/objectcache/RedisBagOStuff.php
b/includes/objectcache/RedisBagOStuff.php
index b8a0dd5..7e506f0 100644
--- a/includes/objectcache/RedisBagOStuff.php
+++ b/includes/objectcache/RedisBagOStuff.php
@@ -372,31 +372,30 @@
}
}
- foreach ( $candidates as $tag ) {
+ while ( ( $tag = array_shift( $candidates ) ) !== false ) {
$server = $this->serverTagMap[$tag];
-
$conn = $this->redisPool->getConnection( $server );
if ( !$conn ) {
continue;
}
- try {
- $info = $conn->info();
- // Check if this server has an unreachable
redis master
- if ( $info['role'] === 'slave'
- && $info['master_link_status'] ===
'down'
- && $this->automaticFailover
- ) {
- // If the master cannot be reached,
fail-over to the next server.
- // If masters are in data-center A, and
slaves in data-center B,
- // this helps avoid the case were
fail-over happens in A but not
- // to the corresponding server in B
(e.g. read/write mismatch).
+ // If automatic failover is enabled, check that the
server's link
+ // to its master (if any) is up -- but only if there
are other
+ // viable candidates left to consider.
+ if ( $this->automaticFailover && $candidates ) {
+ try {
+ if ( $this->getMasterLinkStatus( $conn
) === 'down' ) {
+ // If the master cannot be
reached, fail-over to the next server.
+ // If masters are in
data-center A, and slaves in data-center B,
+ // this helps avoid the case
were fail-over happens in A but not
+ // to the corresponding server
in B (e.g. read/write mismatch).
+ continue;
+ }
+ } catch ( RedisException $e ) {
+ // Server is not accepting commands
+ $this->handleException( $conn, $e );
continue;
}
- } catch ( RedisException $e ) {
- // Server is not accepting commands
- $this->handleException( $conn, $e );
- continue;
}
return array( $server, $conn );
@@ -408,6 +407,19 @@
}
/**
+ * Check the master link status of a Redis server that is configured as
a slave.
+ * @param RedisConnRef $conn
+ * @return string|null Master link status (either 'up' or 'down'), or
null
+ * if the server is not a slave.
+ */
+ protected function getMasterLinkStatus( RedisConnRef $conn ) {
+ $info = $conn->info();
+ return isset( $info['master_link_status'] )
+ ? $info['master_link_status']
+ : null;
+ }
+
+ /**
* Log a fatal error
* @param string $msg
*/
--
To view, visit https://gerrit.wikimedia.org/r/227614
To unsubscribe, visit https://gerrit.wikimedia.org/r/settings
Gerrit-MessageType: newchange
Gerrit-Change-Id: I3812ec5a0b22df122bdf44350bc0496574c02ce8
Gerrit-PatchSet: 1
Gerrit-Project: mediawiki/core
Gerrit-Branch: master
Gerrit-Owner: Ori.livneh <o...@wikimedia.org>
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