Bug#45800 crash when replacing into a merge table and there is a duplicate

      
A REPLACE in the MERGE engine is actually a REPLACE
into one (FIRST or LAST) of the underlying MyISAM
tables. So in effect the server works on the meta
data of the MERGE table, while the real insert happens
in the MyISAM table.

The MERGE table has no index, while MyISAM has a
unique index. When a REPLACE into a MERGE table (
and the REPLACE conflicts with a duplicate in a
child table) is done, we try to access the duplicate
key information for the MERGE table. This information
actually does not exist, hence this results in a crash.

The problem can be resolved by modifying the MERGE
engine to provide us the duplicate key information
directly, instead of just returning the MyISAM index
number as the error key. Then the SQL layer (or "the
server") does not try to access the key_info of the
MERGE table, which does not exist.

The current patch modifies the MERGE engine to provide
the position for a record where a unique key violation
occurs.

1 files changed, 1 insertions, 0 deletions

diff --git a/include/myisammrg.h b/include/myisammrg.h
index 446ecb7d719..31ce3fa47b8 100644
--- a/include/myisammrg.h
+++ b/include/myisammrg.h
@@ -47,6 +47,7 @@ typedef struct st_mymerge_info		/* Struct from h_info */
   ulonglong deleted;			/* Deleted records in database */
   ulonglong recpos;			/* Pos for last used record */
   ulonglong data_file_length;
+  ulonglong dupp_key_pos;               /* Offset of the Duplicate key in the merge table */
   uint	reclength;			/* Recordlength */
   int	errkey;				/* With key was dupplicated on err */
   uint	options;			/* HA_OPTION_... used */