BUG#40337 Fsyncing master and relay log to disk after every event is too slow

NOTE: Backporting the patch to next-mr.
      
The fix proposed in BUG#35542 and BUG#31665 introduces a performance issue
when fsyncing the master.info, relay.info and relay-log.bin* after #th events.
Although such solution has been proposed to reduce the probability of corrupted
files due to a slave-crash, the performance penalty introduced by it has
made the approach impractical for highly intensive workloads.
      
In a nutshell, the option --syn-relay-log proposed in BUG#35542 and BUG#31665
simultaneously fsyncs master.info, relay-log.info and relay-log.bin* and
this is the main source of performance issues.
      
This patch introduces new options that give more control to the user on
what should be fsynced and how often:
      
   1) (--sync-master-info, integer) which syncs the master.info after #th event;
   2) (--sync-relay-log, integer) which syncs the relay-log.bin* after #th
   events.
   3) (--sync-relay-log-info, integer) which syncs the relay.info after #th
   transactions.
      
   To provide both performance and increased reliability, we recommend the following
   setup:
      
   1) --sync-master-info = 0 eventually the operating system will fsync it;
   2) --sync-relay-log = 0 eventually the operating system will fsync it;
   3) --sync-relay-log-info = 1 fsyncs it after every transaction;
      
Notice, that the previous setup does not reduce the probability of
corrupted master.info and relay-log.bin*. To overcome the issue, this patch also
introduces a recovery mechanism that right after restart throws away relay-log.bin*
retrieved from a master and updates the master.info based on the relay.info:
      
      
   4) (--relay-log-recovery, boolean) which enables a recovery mechanism that
   throws away relay-log.bin* after a crash.
      
However, it can only recover the incorrect binlog file and position in master.info,
if other informations (host, port password, etc) are corrupted or incorrect,
then this recovery mechanism will fail to work.

1 files changed, 14 insertions, 1 deletions

diff --git a/sql/rpl_rli.h b/sql/rpl_rli.h
index 171778d9675..a5410dd0c79 100644
--- a/sql/rpl_rli.h
+++ b/sql/rpl_rli.h
@@ -96,6 +96,19 @@ public:
   LOG_INFO linfo;
   IO_CACHE cache_buf,*cur_log;
 
+  /*
+    Keeps track of the number of transactions that commits
+    before fsyncing. The option --sync-relay-log-info determines 
+    how many transactions should commit before fsyncing.
+  */ 
+  uint sync_counter;
+
+  /*
+    Identifies when the recovery process is going on.
+    See sql/slave.cc:init_recovery for further details.
+  */ 
+  bool is_relay_log_recovery;
+
   /* The following variables are safe to read any time */
 
   /* IO_CACHE of the info file - set only during init or end */
@@ -267,7 +280,7 @@ public:
   char slave_patternload_file[FN_REFLEN]; 
   size_t slave_patternload_file_size;  
 
-  Relay_log_info();
+  Relay_log_info(bool is_slave_recovery);
   ~Relay_log_info();
 
   /*