What does the first part of the MariaDB version string mean?

Question

If I inspect the DB version information from within PHP, MariaDB returns an extra set of version numbers at the front of its version string.

Answer 1

The version prefix (so called "replication version hack") was introduced when MariaDB bumped the major version number to 10 (2 digits).

This was necessary, since the replication protocol expects a 1-digit major version number and would break with a 2 digit version number.

The version 5.5.5 was never released.

From Connector/C source:

#define MA_RPL_VERSION_HACK "5.5.5-"
...
mysql->server_version= strdup(end + sizeof(MA_RPL_VERSION_HACK) - 1);