This patch is a part of work on bug #5731 "key_buffer_size not properly restricted to 4GB".

  
The patch limits read_buffer_size and read_rnd_buffer_size by 2 GB on all platforms for the following reasons:
  
- I/O code in mysys, code in mf_iocache.c and in some storage engines do not currently work with sizes > 2 GB for those buffers
- even if the above had been fixed, Windows POSIX read() and write() calls are not 2GB-safe, so setting those buffer to sizes > 2GB would not work correctly on 64-bit Windows.

include/my_global.h

@@ -808,9 +808,6 @@ typedef SOCKET_SIZE_TYPE size_socket;
 #define DBL_MAX		1.79769313486231470e+308
 #define FLT_MAX		((float)3.40282346638528860e+38)
 #endif
-#ifndef SSIZE_MAX
-#define SSIZE_MAX ((~((size_t) 0)) / 2)
-#endif
 
 #if !defined(HAVE_ISINF) && !defined(isinf)
 #define isinf(X)    0

mysql-test/r/bdb_notembedded.result

+set autocommit=1;
+reset master;
+create table bug16206 (a int);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+show binlog events;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+f	n	Format_desc	1	n	Server ver: VERSION, Binlog ver: 4
+f	n	Query	1	n	use `test`; create table bug16206 (a int)
+f	n	Query	1	n	use `test`; insert into bug16206 values(1)
+f	n	Query	1	n	use `test`; insert into bug16206 values(2)
+drop table bug16206;
+reset master;
+create table bug16206 (a int) engine=         bdb;
+insert into bug16206 values(0);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+insert into bug16206 values(3);
+show binlog events;
+Log_name	Pos	Event_type	Server_id	End_log_pos	Info
+f	n	Format_desc	1	n	Server ver: VERSION, Binlog ver: 4
+f	n	Query	1	n	use `test`; create table bug16206 (a int) engine=         bdb
+f	n	Query	1	n	use `test`; insert into bug16206 values(0)
+f	n	Query	1	n	use `test`; insert into bug16206 values(1)
+f	n	Query	1	n	use `test`; BEGIN
+f	n	Query	1	n	use `test`; insert into bug16206 values(2)
+f	n	Query	1	n	use `test`; COMMIT
+f	n	Query	1	n	use `test`; insert into bug16206 values(3)
+drop table bug16206;
+set autocommit=0;
+End of 5.0 tests

mysql-test/t/bdb_notembedded.test

+-- source include/not_embedded.inc
+-- source include/have_bdb.inc
+
+#
+# Bug #16206: Superfluous COMMIT event in binlog when updating BDB in autocommit mode
+#
+set autocommit=1;
+
+let $VERSION=`select version()`;
+
+reset master;
+create table bug16206 (a int);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+--replace_result $VERSION VERSION
+--replace_column 1 f 2 n 5 n
+show binlog events;
+drop table bug16206;
+
+reset master;
+create table bug16206 (a int) engine=         bdb;
+insert into bug16206 values(0);
+insert into bug16206 values(1);
+start transaction;
+insert into bug16206 values(2);
+commit;
+insert into bug16206 values(3);
+--replace_result $VERSION VERSION
+--replace_column 1 f 2 n 5 n
+show binlog events;
+drop table bug16206;
+
+set autocommit=0;
+
+
+--echo End of 5.0 tests

sql/mysqld.cc

@@ -5948,7 +5948,7 @@ The minimum value for this variable is 4096.",
    "Each thread that does a sequential scan allocates a buffer of this size for each table it scans. If you do many sequential scans, you may want to increase this value.",
    (gptr*) &global_system_variables.read_buff_size,
    (gptr*) &max_system_variables.read_buff_size,0, GET_ULONG, REQUIRED_ARG,
-   128*1024L, IO_SIZE*2+MALLOC_OVERHEAD, SSIZE_MAX, MALLOC_OVERHEAD, IO_SIZE,
+   128*1024L, IO_SIZE*2+MALLOC_OVERHEAD, INT_MAX32, MALLOC_OVERHEAD, IO_SIZE,
    0},
   {"read_only", OPT_READONLY,
    "Make all non-temporary tables read-only, with the exception for replication (slave) threads and users with the SUPER privilege",
@@ -5960,12 +5960,12 @@ The minimum value for this variable is 4096.",
    (gptr*) &global_system_variables.read_rnd_buff_size,
    (gptr*) &max_system_variables.read_rnd_buff_size, 0,
    GET_ULONG, REQUIRED_ARG, 256*1024L, IO_SIZE*2+MALLOC_OVERHEAD,
-   SSIZE_MAX, MALLOC_OVERHEAD, IO_SIZE, 0},
+   INT_MAX32, MALLOC_OVERHEAD, IO_SIZE, 0},
   {"record_buffer", OPT_RECORD_BUFFER,
    "Alias for read_buffer_size",
    (gptr*) &global_system_variables.read_buff_size,
    (gptr*) &max_system_variables.read_buff_size,0, GET_ULONG, REQUIRED_ARG,
-   128*1024L, IO_SIZE*2+MALLOC_OVERHEAD, SSIZE_MAX, MALLOC_OVERHEAD, IO_SIZE, 0},
+   128*1024L, IO_SIZE*2+MALLOC_OVERHEAD, INT_MAX32, MALLOC_OVERHEAD, IO_SIZE, 0},
 #ifdef HAVE_REPLICATION
   {"relay_log_purge", OPT_RELAY_LOG_PURGE,
    "0 = do not purge relay logs. 1 = purge them as soon as they are no more needed.",