diff --git a/sql/filesort.cc b/sql/filesort.cc
index de7fc5475fb..c2d3985454c 100644
--- a/sql/filesort.cc
+++ b/sql/filesort.cc
@@ -346,8 +346,8 @@ SORT_INFO *filesort(THD *thd, TABLE *table, Filesort *filesort,
   if (param.tmp_buffer.alloc(param.sort_length))
     goto err;
 
-  if (open_cached_file(&buffpek_pointers,mysql_tmpdir,TEMP_PREFIX,
-		       DISK_BUFFER_SIZE, MYF(MY_WME)))
+  if (open_cached_file(&buffpek_pointers, mysql_tmpdir, TEMP_PREFIX,
+                       DISK_CHUNK_SIZE, MYF(MY_WME)))
     goto err;
 
   param.sort_form= table;
@@ -397,10 +397,10 @@ SORT_INFO *filesort(THD *thd, TABLE *table, Filesort *filesort,
     sort->buffpek.length= maxbuffer;
     buffpek= (Merge_chunk *) sort->buffpek.str;
     close_cached_file(&buffpek_pointers);
-	/* Open cached file if it isn't open */
+    /* Open cached file if it isn't open */
     if (! my_b_inited(outfile) &&
-	open_cached_file(outfile,mysql_tmpdir,TEMP_PREFIX,READ_RECORD_BUFFER,
-			  MYF(MY_WME)))
+        open_cached_file(outfile, mysql_tmpdir, TEMP_PREFIX, DISK_CHUNK_SIZE,
+                         MYF(MY_WME)))
       goto err;
     if (reinit_io_cache(outfile,WRITE_CACHE,0L,0,0))
       goto err;
@@ -1065,7 +1065,7 @@ write_keys(Sort_param *param,  SORT_INFO *fs_info, uint count,
   fs_info->sort_buffer(param, count);
 
   if (!my_b_inited(tempfile) &&
-      open_cached_file(tempfile, mysql_tmpdir, TEMP_PREFIX, DISK_BUFFER_SIZE,
+      open_cached_file(tempfile, mysql_tmpdir, TEMP_PREFIX, DISK_CHUNK_SIZE,
                        MYF(MY_WME)))
     DBUG_RETURN(1);                                /* purecov: inspected */
   /* check we won't have more buffpeks than we can possibly keep in memory */
@@ -1647,8 +1647,8 @@ int merge_many_buff(Sort_param *param, Sort_buffer sort_buffer,
   if (*maxbuffer < MERGEBUFF2)
     DBUG_RETURN(0);				/* purecov: inspected */
   if (flush_io_cache(t_file) ||
-      open_cached_file(&t_file2,mysql_tmpdir,TEMP_PREFIX,DISK_BUFFER_SIZE,
-			MYF(MY_WME)))
+      open_cached_file(&t_file2, mysql_tmpdir, TEMP_PREFIX, DISK_CHUNK_SIZE,
+                       MYF(MY_WME)))
     DBUG_RETURN(1);				/* purecov: inspected */
 
   from_file= t_file ; to_file= &t_file2;
diff --git a/sql/optimizer_costs.h b/sql/optimizer_costs.h
index 2d737d8cf50..30033953021 100644
--- a/sql/optimizer_costs.h
+++ b/sql/optimizer_costs.h
@@ -172,7 +172,7 @@ static inline double cache_hit_ratio(uint ratio)
 #define HEAP_TEMPTABLE_LOOKUP_COST 0.05
 #define HEAP_TEMPTABLE_CREATE_COST 1.0
 #define DISK_TEMPTABLE_LOOKUP_COST 1.0
-#define DISK_TEMPTABLE_CREATE_COST 4.0 /* Creating and deleting 2 temp tables */
+#define DISK_TEMPTABLE_CREATE_COST TMPFILE_CREATE_COST*2 /* 2 tmp tables */
 #define DISK_TEMPTABLE_BLOCK_SIZE  8192
 
 #define SORT_INDEX_CMP_COST 0.02
diff --git a/sql/sql_const.h b/sql/sql_const.h
index 9d92ef4f9da..59faf94dd15 100644
--- a/sql/sql_const.h
+++ b/sql/sql_const.h
@@ -119,14 +119,13 @@
 #define CREATE_MODE	0			/* Default mode on new files */
 #define NAMES_SEP_CHAR	255			/* Char to sep. names */
 
-#define READ_RECORD_BUFFER	(uint) (IO_SIZE*8) /* Pointer_buffer_size */
-#define DISK_BUFFER_SIZE	(uint) (IO_SIZE*16) /* Size of diskbuffer */
-
 /*
-  When reading big blocks, assume that each block of this size is
-  is of simlar cost as key lookup (1)
+   This is used when reading large blocks, sequential read.
+   We assume that reading this much will be the same cost as 1 seek / fetching
+   one row from the storage engine.
 */
-#define DISK_FAST_READ_SIZE     ((uint) (IO_SIZE*16))
+#define DISK_CHUNK_SIZE	(uint) (65536) /* Size of diskbuffer for tmpfiles */
+#define TMPFILE_CREATE_COST        2.0  /* Creating and deleting tmp file */
 
 #define FRM_VER_TRUE_VARCHAR (FRM_VER+4) /* 10 */
 #define FRM_VER_EXPRESSSIONS (FRM_VER+5) /* 11 */
diff --git a/sql/sql_update.cc b/sql/sql_update.cc
index 2da95904419..45a7da787ad 100644
--- a/sql/sql_update.cc
+++ b/sql/sql_update.cc
@@ -840,8 +840,8 @@ int mysql_update(THD *thd,
       explain->buf_tracker.on_scan_init();
       IO_CACHE tempfile;
       if (open_cached_file(&tempfile, mysql_tmpdir,TEMP_PREFIX,
-			   DISK_BUFFER_SIZE, MYF(MY_WME)))
-	goto err;
+                           DISK_CHUNK_SIZE, MYF(MY_WME)))
+        goto err;
 
       /* If quick select is used, initialize it before retrieving rows. */
       if (select && select->quick && select->quick->reset())
diff --git a/sql/uniques.cc b/sql/uniques.cc
index 974218011af..a09655bcaca 100644
--- a/sql/uniques.cc
+++ b/sql/uniques.cc
@@ -103,7 +103,7 @@ Unique::Unique(qsort_cmp2 comp_func, void * comp_func_fixed_arg,
   if (!max_elements)
     max_elements= 1;
 
-  (void) open_cached_file(&file, mysql_tmpdir,TEMP_PREFIX, DISK_BUFFER_SIZE,
+  (void) open_cached_file(&file, mysql_tmpdir, TEMP_PREFIX, DISK_CHUNK_SIZE,
                           MYF(MY_WME));
 }
 
@@ -716,7 +716,7 @@ bool Unique::merge(TABLE *table, uchar *buff, size_t buff_size,
 
   /* Open cached file for table records if it isn't open */
   if (! my_b_inited(outfile) &&
-      open_cached_file(outfile,mysql_tmpdir,TEMP_PREFIX,READ_RECORD_BUFFER,
+      open_cached_file(outfile, mysql_tmpdir, TEMP_PREFIX, DISK_CHUNK_SIZE,
                        MYF(MY_WME)))
     return 1;