branches/zip

Change the read ahead parameter name to innodb_read_ahead_threshold.
Change the meaning of this parameter to signify the number of pages
that must be sequentially accessed for InnoDB to trigger a readahead
request.

Suggested by: Ken

buf/buf0rea.c

@@ -485,7 +485,8 @@ buf_read_ahead_linear(
 
 	/* How many out of order accessed pages can we ignore
 	when working out the access pattern for linear readahead */
-	threshold = ut_min(srv_read_ahead_factor, BUF_READ_AHEAD_AREA);
+	threshold = ut_min((64 - srv_read_ahead_threshold),
+			   BUF_READ_AHEAD_AREA);
 
 	fail_count = 0;
 

handler/ha_innodb.cc

@@ -9950,13 +9950,11 @@ static MYSQL_SYSVAR_STR(change_buffering, innobase_change_buffering,
   innodb_change_buffering_validate,
   innodb_change_buffering_update, NULL);
 
-static MYSQL_SYSVAR_ULONG(read_ahead_factor, srv_read_ahead_factor,
+static MYSQL_SYSVAR_ULONG(read_ahead_threshold, srv_read_ahead_threshold,
   PLUGIN_VAR_RQCMDARG,
-  "Number of pages that may be accessed out of order and InnoDB "
-  "will still issue a readahead."
-  "The higher the value the more relaxed the condition for starting "
-  "readahead.",
-  NULL, NULL, 8, 0, 64, 0);
+  "Number of pages that must be accessed sequentially for InnoDB to"
+  "trigger a readahead.",
+  NULL, NULL, 56, 0, 64, 0);
 
 static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(additional_mem_pool_size),
@@ -10010,7 +10008,7 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(version),
   MYSQL_SYSVAR(use_sys_malloc),
   MYSQL_SYSVAR(change_buffering),
-  MYSQL_SYSVAR(read_ahead_factor),
+  MYSQL_SYSVAR(read_ahead_threshold),
   MYSQL_SYSVAR(io_capacity),
   NULL
 };

include/srv0srv.h

@@ -161,7 +161,7 @@ extern ulint	srv_mem_pool_size;
 extern ulint	srv_lock_table_size;
 
 extern ulint	srv_n_file_io_threads;
-extern ulong	srv_read_ahead_factor;
+extern ulong	srv_read_ahead_threshold;
 extern ulint	srv_n_read_io_threads;
 extern ulint	srv_n_write_io_threads;
 

srv/srv0srv.c

@@ -209,12 +209,10 @@ UNIV_INTERN ulint	srv_n_file_io_threads	= ULINT_MAX;
 UNIV_INTERN ulint	srv_n_read_io_threads	= ULINT_MAX;
 UNIV_INTERN ulint	srv_n_write_io_threads	= ULINT_MAX;
 
-/* User settable value of the number of pages that InnoDB will tolerate
-within a 64 page extent even if they are accessed out of order or have
-not been accessed at all. This number (which varies from 0 to 64) is
-indicative of the slack that we have when deciding about linear
-readahead. */
-UNIV_INTERN ulong	srv_read_ahead_factor	= 8;
+/* User settable value of the number of pages that must be present
+in the buffer cache and accessed sequentially for InnoDB to trigger a
+readahead request. */
+UNIV_INTERN ulong	srv_read_ahead_threshold	= 56;
 
 #ifdef UNIV_LOG_ARCHIVE
 UNIV_INTERN ibool		srv_log_archive_on	= FALSE;