Regex Filter

Overview

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.

Configuration

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

Filter Parameters

The Regex filter has two mandatory parameters: match and replace.

match, options

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 usual. Regex filter does not support the extended-option.

match=TYPE[ ]*=
options=case

replace

This is the text that should replace the part of the SQL-query matching the pattern defined in match.

replace=ENGINE =

source

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.

source=127.0.0.1

user

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.

user=john

log_file

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.

log_file=/tmp/regexfilter.log

log_trace

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.

log_trace=true

Examples

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 cannot 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