5.5 merge

1 files changed, 18 insertions, 0 deletions

diff --git a/include/mysql_com.h b/include/mysql_com.h
index e9a24fd767d..be1d727c15a 100644
--- a/include/mysql_com.h
+++ b/include/mysql_com.h
@@ -34,6 +34,24 @@
 #define MYSQL50_TABLE_NAME_PREFIX_LENGTH  (sizeof(MYSQL50_TABLE_NAME_PREFIX)-1)
 #define SAFE_NAME_LEN (NAME_LEN + MYSQL50_TABLE_NAME_PREFIX_LENGTH)
 
+/*
+  MDEV-4088
+
+  MySQL (and MariaDB 5.x before the fix) was using the first character of the
+  server version string (as sent in the first handshake protocol packet) to
+  decide on the replication event formats. And for 10.x the first character
+  is "1", which the slave thought comes from some ancient 1.x version
+  (ignoring the fact that the first ever MySQL version was 3.x).
+
+  To support replication to these old clients, we fake the version in the
+  first handshake protocol packet to start from "5.5.5-" (for example,
+  it might be "5.5.5-10.0.1-MariaDB-debug-log".
+
+  On the client side we remove this fake version prefix to restore the
+  correct server version. The version "5.5.5" did not support
+  pluggable authentication, so any version starting from "5.5.5-" and
+  claiming to support pluggable auth, must be using this fake prefix.
+*/
 #ifdef EMBEDDED_LIBRARY
 #define RPL_VERSION_HACK ""
 #else