bk commit into 4.0 tree (1.1477)

Below is the list of changes that have just been committed into a local
4.0 repository of guilhem. When guilhem does a push these changes will
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ChangeSet
  1.1477 03/04/27 22:29:24 guilhem@xxxxxxxxx +3 -0
  User-friendly CHANGE MASTER TO MASTER_LOG_POS=0
  and SHOW BINLOG EVENTS FROM 0

  sql/unireg.h
    1.18 03/04/27 22:29:23 guilhem@xxxxxxxxx +6 -2
    warning comment

  sql/sql_yacc.yy
    1.206 03/04/27 22:29:23 guilhem@xxxxxxxxx +12 -0
    User-friendly CHANGE MASTER TO:
    presently when one does CHANGE MASTER TO MASTER_LOG_POS=0 he gets
    030425 10:12:41  Slave I/O thread: connected to master 
'root@localhost:3306',  r
    eplication started in log 'gbichot-bin.013' at position 151
    030425 10:12:41  Error reading packet from server: Client requested master 
to st
    art replication from impossible position (server_errno=1236)
    030425 10:12:41  Got fatal error 1236: 'Client requested master to start 
replica
    tion from impossible position' from master when reading data from binary log
    030425 10:12:41  Slave I/O thread exiting, read up to log 
'gbichot-bin.013', pos
    ition 151
    
    while she/he probably just wanted to start at the beginning of the
    binlog, which is 4. So we silently convert <4 to 4 in sql_yacc.yy
    (i.e. in the slave code; fortunately all versions have the same
    BIN_LOG_HEADER_SIZE=4 and we should not change this). See comments
    for an explaination of why we have to do this in sql_yacc.yy,
    not in sql_repl.cc.
    
    RELAY_LOG_POS does not have the problem (so no change).

  sql/sql_repl.cc
    1.94 03/04/27 22:29:22 guilhem@xxxxxxxxx +1 -7
    SHOW BINLOG EVENTS FROM 0: currently one gets
    MASTER> show binlog events from 0;
    ERROR 1220: Error when executing command SHOW BINLOG EVENTS: Invalid log 
position

# This is a BitKeeper patch.  What follows are the unified diffs for the
# set of deltas contained in the patch.  The rest of the patch, the part
# that BitKeeper cares about, is below these diffs.
# User: guilhem
# Host: gbichot.local
# Root: /home/mysql_src/mysql-4.0

--- 1.205/sql/sql_yacc.yy       Sun Apr 27 21:12:05 2003
+++ 1.206/sql/sql_yacc.yy       Sun Apr 27 22:29:23 2003
@@ -706,6 +706,18 @@
        MASTER_LOG_POS_SYM EQ ulonglong_num
        {
         Lex->mi.pos = $3;
+         /* 
+            If the user specified a value < BIN_LOG_HEADER_SIZE, adjust it
+            instead of causing subsequent errors. 
+            We need to do it in this file, because only there we know that 
+            MASTER_LOG_POS has been explicitely specified. On the contrary
+            in change_master() (sql_repl.cc) we cannot distinguish between 0
+            (MASTER_LOG_POS explicitely specified as 0) and 0 (unspecified),
+            whereas we want to distinguish (specified 0 means "read the binlog
+            from 0" (4 in fact), unspecified means "don't change the position
+            (keep the preceding value)").
+         */
+         Lex->mi.pos = max(BIN_LOG_HEADER_SIZE, Lex->mi.pos);
        }
        |
        MASTER_CONNECT_RETRY_SYM EQ ULONG_NUM

--- 1.17/sql/unireg.h   Wed Mar  5 18:43:53 2003
+++ 1.18/sql/unireg.h   Sun Apr 27 22:29:23 2003
@@ -129,9 +129,13 @@
  */
 #define MIN_TURBOBM_PATTERN_LEN 3
 
-/* Defines for binary logging */
+/* 
+   Defines for binary logging.
+   Do not decrease the value of BIN_LOG_HEADER_SIZE.
+   Do not even increase it before checking code.
+*/
 
-#define BIN_LOG_HEADER_SIZE    4
+#define BIN_LOG_HEADER_SIZE    4 
 
        /* Include prototypes for unireg */
 

--- 1.93/sql/sql_repl.cc        Sun Apr 27 21:12:05 2003
+++ 1.94/sql/sql_repl.cc        Sun Apr 27 22:29:22 2003
@@ -961,7 +961,7 @@
   {
     LEX_MASTER_INFO *lex_mi = &thd->lex.mi;
     ha_rows event_count, limit_start, limit_end;
-    my_off_t pos = lex_mi->pos;
+    my_off_t pos = max(BIN_LOG_HEADER_SIZE, lex_mi->pos); // user-friendly
     char search_file_name[FN_REFLEN], *name;
     const char *log_file_name = lex_mi->log_file_name;
     pthread_mutex_t *log_lock = mysql_bin_log.get_log_lock();
@@ -988,12 +988,6 @@
 
     if ((file=open_binlog(&log, linfo.log_file_name, &errmsg)) < 0)
       goto err;
-
-    if (pos < 4)
-    {
-      errmsg = "Invalid log position";
-      goto err;
-    }
 
     pthread_mutex_lock(log_lock);
     my_b_seek(&log, pos);

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