Merge "Avoid unnecessary WaitConditionLoop delays in ChronologyProtector"

[lhc/web/wiklou.git] / includes / libs / rdbms / ChronologyProtector.php

diff --git a/includes/libs/rdbms/ChronologyProtector.php b/includes/libs/rdbms/ChronologyProtector.php
index 90e697e..8b21ede 100644 (file)
--- a/includes/libs/rdbms/ChronologyProtector.php
+++ b/includes/libs/rdbms/ChronologyProtector.php
@@ -63,6 +63,8 @@ class ChronologyProtector implements LoggerAwareInterface {
 
        /** @var int Seconds to store positions */
        const POSITION_TTL = 60;
+       /** @var int Seconds to store position write index cookies (safely less than POSITION_TTL) */
+       const POSITION_COOKIE_TTL = 60;
        /** @var int Max time to wait for positions to appear */
        const POS_STORE_WAIT_TIMEOUT = 5;
 
@@ -190,13 +192,14 @@ class ChronologyProtector implements LoggerAwareInterface {
                        implode( ', ', array_keys( $this->shutdownPositions ) ) . "\n"
                );
 
-               // CP-protected writes should overwhemingly go to the master datacenter, so get DC-local
-               // lock to merge the values. Use a DC-local get() and a synchronous all-DC set(). This
-               // makes it possible for the BagOStuff class to write in parallel to all DCs with one RTT.
+               // CP-protected writes should overwhelmingly go to the master datacenter, so use a
+               // DC-local lock to merge the values. Use a DC-local get() and a synchronous all-DC
+               // set(). This makes it possible for the BagOStuff class to write in parallel to all
+               // DCs with one RTT. The use of WRITE_SYNC avoids needing READ_LATEST for the get().
                if ( $store->lock( $this->key, 3 ) ) {
                        if ( $workCallback ) {
-                               // Let the store run the work before blocking on a replication sync barrier. By the
-                               // time it's done with the work, the barrier should be fast if replication caught up.
+                               // Let the store run the work before blocking on a replication sync barrier.
+                               // If replication caught up while the work finished, the barrier will be fast.
                                $store->addBusyCallback( $workCallback );
                        }
                        $ok = $store->set(