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.

>>> DB::connection()->getPdo()->getAttribute(PDO::ATTR_SERVER_VERSION);
=> "5.5.5-10.2.20-MariaDB-1:10.2.20+maria~bionic"

What does the 5.5.5 represent?

SO is for programming questions when you're having issues with your code. Since this question doesn't have anything to do with programming, I'm voting to close it. — M. Eriksson, Jun 14 '19 at 15:41
Execute the query: `show variables where variable_name like '%version%' ` and see what you get. My suspicion is that it is the `innodb_version`. — KIKO Software, Jun 14 '19 at 15:42
Hmmm... I just ran `$pdo->getAttribute(PDO::ATTR_SERVER_VERSION)` on my dev box and got `5.5.5-10.1.30-MariaDB` ... my innodb version is `5.6.36-82.2` ... I'm going to hazard a guess that PDO hedges its bets with MariaDB versions when you request `PDO::ATTR_SERVER_VERSION`; I suspect `5.5.5` and `10.1.30` were the stable versions of the 5.x and 10.x branches when I installed MariaDB (currently it's 5.5.65 and 10.1.40 ... or 10.2.24 ... or 10.3.15 ... ho hum). — CD001, Jun 14 '19 at 15:54

score 5 · Accepted Answer · answered Jun 15 '19 at 05:00

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);

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