MDEV-10963 Fragmented BINLOG query

The problem was originally stated in
  http://bugs.mysql.com/bug.php?id=82212
The size of an base64-encoded Rows_log_event exceeds its
vanilla byte representation in 4/3 times.
When a binlogged event size is about 1GB mysqlbinlog generates
a BINLOG query that can't be send out due to its size.

It is fixed with fragmenting the BINLOG argument C-string into
(approximate) halves when the base64 encoded event is over 1GB size.
The mysqlbinlog in such case puts out

    SET @binlog_fragment_0='base64-encoded-fragment_0';
    SET @binlog_fragment_1='base64-encoded-fragment_1';
    BINLOG @binlog_fragment_0, @binlog_fragment_1;

to represent a big BINLOG.
For prompt memory release BINLOG handler is made to reset the BINLOG argument
user variables in the middle of processing, as if @binlog_fragment_{0,1} = NULL
is assigned.

Notice the 2 fragments are enough, though the client and server still may
need to tweak their @@max_allowed_packet to satisfy to the fragment
size (which they would have to do anyway with greater number of
fragments, should that be desired).

On the lower level the following changes are made:

Log_event::print_base64()
  remains to call encoder and store the encoded data into a cache but
  now *without* doing any formatting. The latter is left for time
  when the cache is copied to an output file (e.g mysqlbinlog output).
  No formatting behavior is also reflected by the change in the meaning
  of the last argument which specifies whether to cache the encoded data.

Rows_log_event::print_helper()
  is made to invoke a specialized fragmented cache-to-file copying function
  which is

copy_cache_to_file_wrapped()
  that takes care of fragmenting also optionally wraps encoded
  strings (fragments) into SQL stanzas.

my_b_copy_to_file()
  is refactored to into my_b_copy_all_to_file(). The former function
  is generalized
  to accepts more a limit argument to constraint the copying and does
  not reinitialize anymore the cache into reading mode.
  The limit does not do any effect on the fully read cache.

1 files changed, 10 insertions, 3 deletions

diff --git a/sql/log_event.h b/sql/log_event.h
index 90900f63533..446bd8cb827 100644
--- a/sql/log_event.h
+++ b/sql/log_event.h
@@ -1157,7 +1157,7 @@ public:
   void print_header(IO_CACHE* file, PRINT_EVENT_INFO* print_event_info,
                     bool is_more);
   void print_base64(IO_CACHE* file, PRINT_EVENT_INFO* print_event_info,
-                    bool is_more);
+                    bool do_print_encoded);
 #endif
   /*
     read_log_event() functions read an event from a binlog or relay
@@ -4891,15 +4891,22 @@ public:
   virtual int get_data_size() { return IGNORABLE_HEADER_LEN; }
 };
 
+#ifdef MYSQL_CLIENT
+void copy_cache_to_file_wrapped(FILE *file,
+                                PRINT_EVENT_INFO *print_event_info,
+                                IO_CACHE *body,
+                                bool do_wrap);
+#endif
 
 static inline bool copy_event_cache_to_file_and_reinit(IO_CACHE *cache,
                                                        FILE *file)
 {
-  return         
-    my_b_copy_to_file(cache, file) ||
+  return
+    my_b_copy_all_to_file(cache, file) ||
     reinit_io_cache(cache, WRITE_CACHE, 0, FALSE, TRUE);
 }
 
+
 #ifdef MYSQL_SERVER
 /*****************************************************************************