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MySQL 5.7 Reference Manual  / ...  / Replication  / Configuring Replication  / MySQL Multi-Source Replication  /  Provisioning a Multi-Source Replica for GTID-Based Replication

16.1.5.2 Provisioning a Multi-Source Replica for GTID-Based Replication

If the sources in the multi-source replication topology have existing data, it can save time to provision the replica with the relevant data before starting replication. In a multi-source replication topology, copying the data directory cannot be used to provision the replica with data from all of the sources, and you might also want to replicate only specific databases from each source. The best strategy for provisioning such a replica is therefore to usemysqldump to create an appropriate dump file on each source, then use themysql client to import the dump file on the replica.

If you are using GTID-based replication, you need to pay attention to theSET @@GLOBAL.gtid_purged statement thatmysqldump places in the dump output. This statement transfers the GTIDs for the transactions executed on the source to the replica, and the replica requires this information. However, for any case more complex than provisioning one new, empty replica from one source, you need to check what effect the statement has in the replica's version of MySQL, and handle the statement accordingly. The following guidance summarizes suitable actions, but for more details, see themysqldump documentation.

In MySQL 5.6 and 5.7, theSET @@GLOBAL.gtid_purged statement written bymysqldump replaces the value ofgtid_purged on the replica. Also in those releases that value can only be changed when the replica's record of transactions with GTIDs (thegtid_executed set) is empty. In a multi-source replication topology, you must therefore remove theSET @@GLOBAL.gtid_purged statement from the dump output before replaying the dump files, because you cannot apply a second or subsequent dump file including this statement. As an alternative to removing theSET @@GLOBAL.gtid_purged statement, if you are provisioning the replica with two partial dumps from the same source, and the GTID set in the second dump is the same as the first (so no new transactions have been executed on the source in between the dumps), you can setmysqldump's--set-gtid-purged option toOFF when you output the second dump file, to omit the statement.

For MySQL 5.6 and 5.7, these limitations mean all the dump files from the sources must be applied in a single operation on a replica with an emptygtid_executed set. You can clear a replica's GTID execution history by issuingRESET MASTER on the replica, but if you have other, wanted transactions with GTIDs on the replica, choose an alternative method of provisioning from those described inSection 16.1.3.5, “Using GTIDs for Failover and Scaleout”.

In the following provisioning example, we assume that theSET @@GLOBAL.gtid_purged statement needs to be removed from the files and handled manually. We also assume that there are no wanted transactions with GTIDs on the replica before provisioning starts.

  1. To create dump files for a database nameddb1 onsource1 and a database nameddb2 onsource2, runmysqldump forsource1 as follows:

    mysqldump -u<user> -p<password> --single-transaction --triggers --routines --set-gtid-purged=ON --databases db1 > dumpM1.sql

    Then runmysqldump forsource2 as follows:

    mysqldump -u<user> -p<password> --single-transaction --triggers --routines --set-gtid-purged=ON --databases db2 > dumpM2.sql

  2. Record thegtid_purged value thatmysqldump added to each of the dump files. For example, for dump files created on MySQL 5.6 or 5.7, you can extract the value like this:

    cat dumpM1.sql | grep GTID_PURGED | cut -f2 -d'=' | cut -f2 -d$'\''cat dumpM2.sql | grep GTID_PURGED | cut -f2 -d'=' | cut -f2 -d$'\''

    The result in each case should be a GTID set, for example:

    source1:   2174B383-5441-11E8-B90A-C80AA9429562:1-1029source2:   224DA167-0C0C-11E8-8442-00059A3C7B00:1-2695

  3. Remove the line from each dump file that contains theSET @@GLOBAL.gtid_purged statement. For example:

    sed '/GTID_PURGED/d' dumpM1.sql > dumpM1_nopurge.sqlsed '/GTID_PURGED/d' dumpM2.sql > dumpM2_nopurge.sql

  4. Use themysql client to import each edited dump file into the replica. For example:

    mysql -u<user> -p<password> < dumpM1_nopurge.sqlmysql -u<user> -p<password> < dumpM2_nopurge.sql

  5. On the replica, issueRESET MASTER to clear the GTID execution history (assuming, as explained above, that all the dump files have been imported and that there are no wanted transactions with GTIDs on the replica). Then issue aSET @@GLOBAL.gtid_purged statement to set thegtid_purged value to the union of all the GTID sets from all the dump files, as you recorded in Step 2. For example:

    mysql> RESET MASTER;mysql> SET @@GLOBAL.gtid_purged = "2174B383-5441-11E8-B90A-C80AA9429562:1-1029, 224DA167-0C0C-11E8-8442-00059A3C7B00:1-2695";

    If there are, or might be, overlapping transactions between the GTID sets in the dump files, you can use the stored functions described inSection 16.1.3.7, “Stored Function Examples to Manipulate GTIDs” to check this beforehand and to calculate the union of all the GTID sets.