Basic Filters

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Maxwell can be configured to filter out updates from specific tables. This is controlled by the --filter command line flag.

Example 1

--filter = 'exclude: foodb.*, include: foodb.tbl, include: foodb./table_\d+/'

This example tells Maxwell to suppress all updates that happen on foodb, except for updates to tbl and any table in foodb matching the regexp /table_\d+/.

Example 2

Filter options are evaluated in the order specified, so in this example we suppress everything except updates in the db1 database.

--filter = 'exclude: *.*, include: db1.*'

Column Filters

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Maxwell can also include/exclude based on column values:

--filter = 'exclude: db.tbl.col = reject'

will reject any row in db.tbl that contains col and where the stringified value of "col" is "reject". Column filters are ignored if the specified column is not present, so --filter = 'exclude: *.*.col_a = *' will exclude updates to any table that contains col_a, but include every other table.

Blacklisting

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In rare cases, you may wish to tell Maxwell to completely ignore a database or table, including schema changes. In general, don't use this. If you must use this:

--filter = 'blacklist: bad_db.*'

Note that once Maxwell has been running with a table or database marked as blacklisted, you must continue to run Maxwell with that table or database blacklisted or else Maxwell will halt. If you want to stop blacklisting a table or database, you will have to drop the maxwell schema first. Also note that this is the feature I most regret writing.

Javascript Filters

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If you need more flexibility than the native filters provide, you can write a small chunk of javascript for Maxwell to pass each row through with --javascript FILE. This file should contain at least a javascript function named process_row. This function will be passed a WrappedRowMap object that represents the current row and a LinkedHashMap<String, Object> which represents a global state and is free to make filtering and data munging decisions:

function process_row(row, state) {
    // Updating the state object
    if ( row.database == "test" && row.table == "lock") {
        var haslock = row.data.get("haslock");
        if ( haslock == "false" ) {
            state.put("haslock", "false");
        } else if( haslock == "true" ) {
            state.put("haslock", "true");
        }
    }

    // Suppressing rows based on state
    if(state.get("haslock") == "true") {
        row.suppress();
    }

    // Filter and Change based on actual data
    if ( row.database == "test" && row.table == "bar" ) {
        var username = row.data.get("username");
        if ( username == "osheroff" )
            row.suppress();

        row.data.put("username", username.toUpperCase());
    }
}

There's a longer example here: https://github.com/zendesk/maxwell/blob/master/src/example/filter.js.