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Description

Chunjun jdbc source connector start to consume an DB table，sometimes the table contains a massive historical data，in order to skipping historical data consuming. By now ,We can set param startLocation that corresponding with increColumn，but that is extremely troublesome.

In order to simplify the configuartion of Chunjun task，There can be a means that set a flag to inform the source task，avoiding consume historical data from db to consume latest db updates events ，however，param setting of startLocation is not required.

In my opion，can set the param startLocation to a special value token ，for example ‘latest’， In [JdbcInputFormat],

https://github.com/DTStack/chunjun/blob/master/chunjun-connectors/chunjun-connector-jdbc-base/src/main/java/com/dtstack/chunjun/connector/jdbc/source/JdbcInputFormat.java#L146-L164

if startLocation is latest, then execute the getMaxValueFromDb() to get the max value of increColumn, finally , to create JdbcInputSplit, the Pseudocode as below：

public JdbcInputSplit[] createSplitsInternalBySplitMod(int minNumSplits, String startLocation) {
        JdbcInputSplit[] splits = new JdbcInputSplit[minNumSplits];
        if (StringUtils.isNotBlank(startLocation)) {
            if ("latest".equals(startLocation)) {
              
                String maxValueFromDb = this.getMaxValueFromDb();
     
                return new JdbcInputSplit[]{new JdbcInputSplit(
                        0,
                        minNumSplits,
                        0,
                        maxValueFromDb,
                        null,
                        null,
                        null,
                        "mod",
                        jdbcConf.isPolling())};
            }
}

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