bzr commit into mysql-5.1-bugteam branch (v.narayanan:2804) Bug#37282

[V Narayanan]

#At file:///home/narayanan/Work/mysql/W-M/mysql-5.1-bugteam-37282/ based on revid:svoj@stripped

 2804 V Narayanan	2009-02-12
      Bug#37282 LOAD DATA CONCURRENT blocks selects when set to 2 and hole in table
      
      A running LOAD DATA CONCURRENT locks the table, 
      so new SELECT statements must wait for the load to finish. 
      Occurs when concurrent_inserts=2 and there is a hole in 
      the data.
      
      Currently in MyISAM concurrent_inserts = 2 disallows concurrent inserts
      on the table when there are concurrent readers on the table. This causes
      the selects to wait when a load concurrent operation is in progress.
      
      The current patch fixes the behaviour by introducing a new mode
      
      concurrent_inserts = 3
      
      In this mode concurrent inserts are disable only when there are concurrent
      writers and not when there are concurrent readers.
modified:
  sql/mysqld.cc
  storage/myisam/mi_locking.c

per-file messages:
  sql/mysqld.cc
    Increase the maximum value for concurrent_insert to 3.
  storage/myisam/mi_locking.c
    Modified the function mi_check_status to allow concurrent inserts when
    
    a) myisam_concurrent_insert=3 and 
    b) there are no concurrent writers. (This variable 
       is set by setting the global variable concurrent_insert=3).
       (info->s->w_locks)
    
    NOTE: Earlier this function allowed cocurrent inserts only in the following
    condition
    
    a) myisam_concurrent_insert=2
    b) there are no concurrent writers (info->s->w_locks)
    c) there are no concurrent readers (info->s->r_locks)
=== modified file 'sql/mysqld.cc'
--- a/sql/mysqld.cc	2009-02-12 04:44:32 +0000
+++ b/sql/mysqld.cc	2009-02-12 11:59:09 +0000
@@ -5705,7 +5705,7 @@ struct my_option my_long_options[] =
   {"concurrent-insert", OPT_CONCURRENT_INSERT,
    "Use concurrent insert with MyISAM. Disable with --concurrent-insert=0",
    (uchar**) &myisam_concurrent_insert, (uchar**) &myisam_concurrent_insert,
-   0, GET_ULONG, OPT_ARG, 1, 0, 2, 0, 0, 0},
+   0, GET_ULONG, OPT_ARG, 1, 0, 3, 0, 0, 0},
   {"console", OPT_CONSOLE, "Write error output on screen; Don't remove the console window on windows.",
    (uchar**) &opt_console, (uchar**) &opt_console, 0, GET_BOOL, NO_ARG, 0, 0, 0,
    0, 0, 0},

=== modified file 'storage/myisam/mi_locking.c'
--- a/storage/myisam/mi_locking.c	2007-08-13 13:11:25 +0000
+++ b/storage/myisam/mi_locking.c	2009-02-12 11:59:09 +0000
@@ -385,6 +385,32 @@ my_bool mi_check_status(void *param)
   DBUG_PRINT("info",("dellink: %ld  r_locks: %u  w_locks: %u",
                      (long) info->s->state.dellink, (uint) info->s->r_locks,
                      (uint) info->s->w_locks));
+  /*
+    myisam_concurrent_insert == 2 => Allow concurrent insert if
+                                     a) There are no holes in the datafile
+                                     b) There are no concurrent writers on the
+                                        datafile
+                                     c) There are no concurrent readers on the
+                                        datafile
+
+    myisam_concurrent_insert == 3 => Allow concurrent insert if
+                                     a) There are no holes in the data file
+                                     b) There are no concurrent writers on the
+                                        datafile
+
+    For E.g.
+    
+    If t1 is a table that HAS HOLES in it and a we are LOADING DATA CONCURRENTLY
+    into it from a datafile, a SELECT on this table would
+
+    a) WAIT until LOAD completes when  myisam_concurrent_insert == 2
+    b) WILL NOT WAIT for LOAD when myisam_concurrent_insert == 3.
+  */
+  if (myisam_concurrent_insert == 3)
+  {
+     return (my_bool) !(info->s->state.dellink == HA_OFFSET_ERROR ||
+                     (myisam_concurrent_insert == 3 && info->s->w_locks == 1));
+  }
   return (my_bool) !(info->s->state.dellink == HA_OFFSET_ERROR ||
                      (myisam_concurrent_insert == 2 && info->s->r_locks &&
                       info->s->w_locks == 1));