myisamdef.h, mi_locking.c, mi_dynrec.c:

  Fix insert performance with mmap

storage/myisam/mi_dynrec.c

@@ -201,6 +201,7 @@ uint mi_mmap_pwrite(MI_INFO *info, byte *Buffer,
   }
   else
   {
+    info->s->nonmmaped_inserts++;
     if (info->s->concurrent_insert)
       rw_unlock(&info->s->mmap_lock);
     return my_pwrite(info->dfile, Buffer, Count, offset, MyFlags);

storage/myisam/mi_locking.c

@@ -85,11 +85,13 @@ int mi_lock_database(MI_INFO *info, int lock_type)
 	if (share->changed && !share->w_locks)
 	{
 #ifdef HAVE_MMAP
-    if (info->s->mmaped_length != info->s->state.state.data_file_length)
+    if ((info->s->mmaped_length != info->s->state.state.data_file_length) &&
+        (info->s->nonmmaped_inserts > MAX_NONMAPPED_INSERTS))
     {
       if (info->s->concurrent_insert)
         rw_wrlock(&info->s->mmap_lock);
       mi_remap_file(info, info->s->state.state.data_file_length);
+      info->s->nonmmaped_inserts= 0;
       if (info->s->concurrent_insert)
         rw_unlock(&info->s->mmap_lock);
     }

storage/myisam/myisamdef.h

@@ -152,6 +152,7 @@ typedef struct st_mi_isam_pack {
   uchar version;
 } MI_PACK;
 
+#define MAX_NONMAPPED_INSERTS 1000      
 
 typedef struct st_mi_isam_share {	/* Shared between opens */
   MI_STATE_INFO state;
@@ -211,6 +212,8 @@ typedef struct st_mi_isam_share {	/* Shared between opens */
   rw_lock_t *key_root_lock;
 #endif
   my_off_t mmaped_length;
+  uint     nonmmaped_inserts;           /* counter of writing in non-mmaped
+                                           area */
   rw_lock_t mmap_lock;
 } MYISAM_SHARE;