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, 33 insertions, 28 deletions

diff --git a/mysys/mf_iocache2.c b/mysys/mf_iocache2.c
index fa3b6e672d7..f3877331664 100644
--- a/mysys/mf_iocache2.c
+++ b/mysys/mf_iocache2.c
@@ -23,51 +23,56 @@
 #include <stdarg.h>
 #include <m_ctype.h>
 
-/*
-  Copy contents of an IO_CACHE to a file.
-
-  SYNOPSIS
-    my_b_copy_to_file()
-    cache  IO_CACHE to copy from
-    file   File to copy to
-
-  DESCRIPTION
-    Copy the contents of the cache to the file. The cache will be
-    re-inited to a read cache and will read from the beginning of the
-    cache.
-
-    If a failure to write fully occurs, the cache is only copied
-    partially.
+/**
+  Copy the cache to the file. Copying can be constrained to @c count
+  number of bytes when the parameter is less than SIZE_T_MAX.  The
+  cache will be optionally re-inited to a read cache and will read
+  from the beginning of the cache.  If a failure to write fully
+  occurs, the cache is only copied partially.
 
   TODO
-    Make this function solid by handling partial reads from the cache
-    in a correct manner: it should be atomic.
-
-  RETURN VALUE
-    0  All OK
-    1  An error occurred
+  Make this function solid by handling partial reads from the cache
+  in a correct manner: it should be atomic.
+
+  @param cache      IO_CACHE to copy from
+  @param file       File to copy to
+  @param count      the copied size or the max of the type
+                    when the whole cache is to be copied.
+  @return
+         0          All OK
+         1          An error occurred
 */
 int
-my_b_copy_to_file(IO_CACHE *cache, FILE *file)
+my_b_copy_to_file(IO_CACHE *cache, FILE *file,
+                  size_t count)
 {
-  size_t bytes_in_cache;
+  size_t curr_write, bytes_in_cache;
   DBUG_ENTER("my_b_copy_to_file");
 
-  /* Reinit the cache to read from the beginning of the cache */
-  if (reinit_io_cache(cache, READ_CACHE, 0L, FALSE, FALSE))
-    DBUG_RETURN(1);
   bytes_in_cache= my_b_bytes_in_cache(cache);
   do
   {
-    if (my_fwrite(file, cache->read_pos, bytes_in_cache,
+    curr_write= MY_MIN(bytes_in_cache, count);
+    if (my_fwrite(file, cache->read_pos, curr_write,
                   MYF(MY_WME | MY_NABP)) == (size_t) -1)
       DBUG_RETURN(1);
-  } while ((bytes_in_cache= my_b_fill(cache)));
+
+    cache->read_pos += curr_write;
+    count -= curr_write;
+  } while (count && (bytes_in_cache= my_b_fill(cache)));
   if(cache->error == -1)
     DBUG_RETURN(1);
   DBUG_RETURN(0);
 }
 
+int my_b_copy_all_to_file(IO_CACHE *cache, FILE *file)
+{
+  DBUG_ENTER("my_b_copy_all_to_file");
+  /* Reinit the cache to read from the beginning of the cache */
+  if (reinit_io_cache(cache, READ_CACHE, 0L, FALSE, FALSE))
+    DBUG_RETURN(1);
+  DBUG_RETURN(my_b_copy_to_file(cache, file, SIZE_T_MAX));
+}
 
 my_off_t my_b_append_tell(IO_CACHE* info)
 {