The Regex filter is a filter module for MariaDB MaxScale that is able to rewrite query content using regular expression matches and text substitution. It uses the PCRE2 syntax which differs from the POSIX regular expressions used in MariaDB MaxScale versions prior to 1.3.0.
For all details about the PCRE2 syntax, please read the PCRE2 syntax documentation.
Please note that the PCRE2 library uses a different syntax to refer to capture groups in the replacement string. The main difference is the usage of the dollar character instead of the backslash character for references e.g.
$1 instead of
\1. For more details about the replacement string differences, please read the Creating a new string with substitutions chapter in the PCRE2 manual.
The configuration block for the Regex filter requires the minimal filter options in its section within the maxscale.cnf file, stored in /etc/maxscale.cnf.
[MyRegexFilter] type=filter module=regexfilter match=some string replace=replacement string [MyService] type=service router=readconnroute servers=server1 user=myuser password=mypasswd filters=MyRegexfilter
The Regex filter has two mandatory parameters: match and replace.
match is a PCRE2 regular expression which defines the text in the SQL statements that is replaced.
The options-parameter affects how the patterns are compiled as
Regex filter does not support the
match=TYPE[ ]*= options=case
This is the text that should replace the part of the SQL-query matching the pattern defined in match.
The optional source parameter defines an address that is used to match against the address from which the client connection to MariaDB MaxScale originates. Only sessions that originate from this address will have the match and replacement applied to them.
The optional user parameter defines a user name that is used to match against the user from which the client connection to MariaDB MaxScale originates. Only sessions that are connected using this username will have the match and replacement applied to them.
The optional log_file parameter defines a log file in which the filter writes all queries that are not matched and matching queries with their replacement queries. All sessions will log to this file so this should only be used for diagnostic purposes.
The optional log_trace parameter toggles the logging of non-matching and matching queries with their replacements into the log file on the info level. This is the preferred method of diagnosing the matching of queries since the log level can be changed at runtime. For more details about logging levels and session specific logging, please read the Configuration Guide and the MaxAdmin documentation on changing the logging levels.
Example 1 - Replace MySQL 5.1 create table syntax with that for later versions
MySQL 5.1 used the parameter TYPE = to set the storage engine that should be used for a table. In later versions this changed to be ENGINE =. Imagine you have an application that you can not change for some reason, but you wish to migrate to a newer version of MySQL. The regexfilter can be used to transform the create table statements into the form that could be used by MySQL 5.5
[CreateTableFilter] type=filter module=regexfilter options=ignorecase match=TYPE\s*= replace=ENGINE= [MyService] type=service router=readconnroute servers=server1 user=myuser password=mypasswd filters=CreateTableFilter