bk commit into maria tree (bell:1.2613) BUG#34712

[sanja]

Below is the list of changes that have just been committed into a local
maria repository of bell.  When bell does a push these changes
will be propagated to the main repository and, within 24 hours after the
push, to the public repository.
For information on how to access the public repository
see http://dev.mysql.com/doc/mysql/en/installing-source-tree.html

ChangeSet@stripped, 2008-03-07 10:02:30+02:00, bell@stripped +1 -0
  Avoiding changing log on flush call
  if nothing was added to the log
  (BUG#34712 maria_read_log changes log
  file content on several platforms though not needed)

  storage/maria/ma_loghandler.c@stripped, 2008-03-07 10:02:25+02:00, bell@stripped +43 -6
    Flag that signaling about "everythig-flushed" state of
    the log added, to avoid changing log on flush request
    if nothing was written but horizon placed on the page boarder.

diff -Nrup a/storage/maria/ma_loghandler.c b/storage/maria/ma_loghandler.c
--- a/storage/maria/ma_loghandler.c	2008-02-29 13:11:24 +02:00
+++ b/storage/maria/ma_loghandler.c	2008-03-07 10:02:25 +02:00
@@ -297,6 +297,11 @@ struct st_translog_descriptor
   pthread_mutex_t purger_lock;
   /* last low water mark checked */
   LSN last_lsn_checked;
+  /*
+    Must be set to 0 under loghandler lock every time a new LSN
+    is generated.
+  */
+  my_bool is_everything_flushed;
 };
 
 static struct st_translog_descriptor log_descriptor;
@@ -3263,6 +3268,7 @@ my_bool translog_init_with_table(const c
 
   id_to_share= NULL;
   log_descriptor.directory_fd= -1;
+  log_descriptor.is_everything_flushed= 1;
 
   (*init_table_func)();
 
@@ -3846,7 +3852,6 @@ my_bool translog_init_with_table(const c
       translog_free_record_header(&rec);
     }
   }
-
   DBUG_RETURN(0);
 }
 
@@ -4586,6 +4591,15 @@ static translog_size_t translog_get_curr
 }
 
 
+/*static inline*/ void set_lsn(LSN *lsn, LSN value)
+{
+  translog_lock_assert_owner();
+  *lsn= value;
+  /* we generate LSN so something is not flushed in log */
+  log_descriptor.is_everything_flushed= 0;
+}
+
+
 /**
    @brief Write variable record in 1 group.
 
@@ -4631,7 +4645,7 @@ translog_write_variable_record_1group(LS
   if (buffer_to_flush)
     translog_buffer_lock_assert_owner(buffer_to_flush);
 
-  *lsn= horizon= log_descriptor.horizon;
+  set_lsn(lsn, horizon= log_descriptor.horizon);
   if (translog_set_lsn_for_files(LSN_FILE_NO(*lsn), LSN_FILE_NO(*lsn),
                                  *lsn, TRUE) ||
       (log_record_type_descriptor[type].inwrite_hook &&
@@ -4780,8 +4794,7 @@ translog_write_variable_record_1chunk(LS
 
   translog_write_variable_record_1group_header(parts, type, short_trid,
                                                header_length, chunk0_header);
-
-  *lsn= log_descriptor.horizon;
+  set_lsn(lsn, log_descriptor.horizon);
   if (translog_set_lsn_for_files(LSN_FILE_NO(*lsn), LSN_FILE_NO(*lsn),
                                  *lsn, TRUE) ||
       (log_record_type_descriptor[type].inwrite_hook &&
@@ -5468,7 +5481,18 @@ translog_write_variable_record_mgroup(LS
     if (first_chunk0)
     {
       first_chunk0= 0;
-      *lsn= horizon;
+
+      /*
+        We can drop "log_descriptor.is_everything_flushed" earlier when have
+        lock on loghandler and assign initial value of "horizon" variable or
+        before unlocking loghandler (because we will increase writers
+        counter on the buffer and every thread which wanted flush the buffer
+        will wait till we finish with it). But IMHO better here take short
+        lock and do not bother other threads with waiting.
+      */
+      translog_lock();
+      set_lsn(lsn, horizon);
+      translog_unlock();
       if (log_record_type_descriptor[type].inwrite_hook &&
           (*log_record_type_descriptor[type].inwrite_hook) (type, trn,
                                                             tbl_info,
@@ -5742,7 +5766,7 @@ static my_bool translog_write_fixed_reco
       translog_buffer_lock_assert_owner(buffer_to_flush);
   }
 
-  *lsn= log_descriptor.horizon;
+  set_lsn(lsn, log_descriptor.horizon);
   if (translog_set_lsn_for_files(LSN_FILE_NO(*lsn), LSN_FILE_NO(*lsn),
                              *lsn, TRUE) ||
       (log_record_type_descriptor[type].inwrite_hook &&
@@ -7293,6 +7317,12 @@ my_bool translog_flush(TRANSLOG_ADDRESS 
 
   pthread_mutex_lock(&log_descriptor.log_flush_lock);
   translog_lock();
+  if (log_descriptor.is_everything_flushed)
+  {
+    DBUG_PRINT("info", ("everything is flushed"));
+    translog_unlock();
+    goto out;
+  }
   flush_horizon= LSN_IMPOSSIBLE;
   old_flushed= log_descriptor.flushed;
   for (;;)
@@ -7338,7 +7368,14 @@ my_bool translog_flush(TRANSLOG_ADDRESS 
             then was at the moment of start flushing);
           */
           if (buffer_start == log_descriptor.bc.buffer_no)
+          {
+            /*
+              We are going to flush last buffer, and will not release
+              log_flush_lock until it happened, so we can set the flag here
+            */
+            log_descriptor.is_everything_flushed= 1;
             translog_force_current_buffer_to_finish();
+          }
         }
         break;
       }