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Add Why Is "Connect to Replica" mode preferred?

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Will Currie 2019-01-16 06:28:05 +11:00 committed by GitHub
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@ -28,3 +28,9 @@ It is therefore unlikely that `gh-ost` will support this behavior.
Yes. TL;DR if running all on same replica/master, make sure to provide `--replica-server-id`. [Read more](cheatsheet.md#concurrent-migrations)
# Why
### Why Is the "Connect to Replica" mode preferred?
To avoid placing extra load on the master. `gh-ost` connects as a replication client. Each additional replica adds some load to the master.
To monitor replication lag from a replica. This makes the replication lag throttle, `--max-lag-millis`, more representative of the lag experienced by other replicas following the master (perhaps N levels deep in a tree of replicas).