bzr commit into mysql-5.1-bugteam branch (v.narayanan:2855) Bug#38848

[Narayanan V]

#At file:///export/home/log/Narayanan/mysql_checkouts_bazaar/5.1_main_repository/mysql-5.1-bugteam-38848/ based on revid:satya.bn@stripped

 2855 Narayanan V	2009-04-08
      Bug#38848 myisam_use_mmap causes widespread myisam corruption on windows
            
      Currently the memory map is being created
      with a size that is greater than the size 
      of the underlying datafile. This can cause
      varying behaviour,
      
      e.g. 
      
      In windows the size of the datafile
      is increased, while on linux it remains
      the same.
      
      This fix removes the increment margin to
      the size that is used while creating the
      memory map.
     @ storage/myisam/mi_dynrec.c
        remove MEMMAP_EXTRA_MARGIN that is used as
        the increment margin to the underlying 
        datafile size while creating the mmap.
     @ storage/myisam/mi_packrec.c
        The size of the underlying datafile is
        increased by MEMMAP_EXTRA_MARGIN when
        using a packed record format. Hence in 
        this case the size of the memory map should 
        be incremented by the same factor.

    modified:
      storage/myisam/mi_dynrec.c
      storage/myisam/mi_packrec.c
=== modified file 'storage/myisam/mi_dynrec.c'
--- a/storage/myisam/mi_dynrec.c	2008-03-31 07:40:39 +0000
+++ b/storage/myisam/mi_dynrec.c	2009-04-08 06:48:43 +0000
@@ -66,7 +66,7 @@ static int _mi_cmp_buffer(File file, con
 my_bool mi_dynmap_file(MI_INFO *info, my_off_t size)
 {
   DBUG_ENTER("mi_dynmap_file");
-  if (size > (my_off_t) (~((size_t) 0)) - MEMMAP_EXTRA_MARGIN)
+  if (size > (my_off_t) (~((size_t) 0)))
   {
     DBUG_PRINT("warning", ("File is too large for mmap"));
     DBUG_RETURN(1);
@@ -80,7 +80,7 @@ my_bool mi_dynmap_file(MI_INFO *info, my
       upon a write if no physical memory is available.
   */
   info->s->file_map= (uchar*)
-                  my_mmap(0, (size_t)(size + MEMMAP_EXTRA_MARGIN),
+                  my_mmap(0, (size_t) size,
                           info->s->mode==O_RDONLY ? PROT_READ :
                           PROT_READ | PROT_WRITE,
                           MAP_SHARED | MAP_NORESERVE,
@@ -113,7 +113,7 @@ void mi_remap_file(MI_INFO *info, my_off
   if (info->s->file_map)
   {
     VOID(my_munmap((char*) info->s->file_map,
-                   (size_t) info->s->mmaped_length + MEMMAP_EXTRA_MARGIN));
+                   (size_t) info->s->mmaped_length));
     mi_dynmap_file(info, size);
   }
 }

=== modified file 'storage/myisam/mi_packrec.c'
--- a/storage/myisam/mi_packrec.c	2009-04-07 11:36:15 +0000
+++ b/storage/myisam/mi_packrec.c	2009-04-08 06:48:43 +0000
@@ -1502,7 +1502,8 @@ my_bool _mi_memmap_file(MI_INFO *info)
       DBUG_PRINT("warning",("File isn't extended for memmap"));
       DBUG_RETURN(0);
     }
-    if (mi_dynmap_file(info, share->state.state.data_file_length))
+    if (mi_dynmap_file(info,
+        share->state.state.data_file_length + MEMMAP_EXTRA_MARGIN))
       DBUG_RETURN(0);
   }
   info->opt_flag|= MEMMAP_USED;


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