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When do secondary subclusters see DDL and DML changes?
GaryG
Administrator
In the presentation, you mentioned DDL like sync happens every 5 minutes ? So secondary subclusters may take 5 minutes or more to see DDL changes ?
I am hoping DML are instantaneous.
Question asked at the 2020 Big Data Conference presentation Sizing and Configuring Vertica in Eon Mode for Different Use Cases given by @skeswani and @skamat .
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Answers
When do secondary subclusters see DDL and DML changes? - immediately on commit.
The secondary (or entire cluster) sees the catalog changes right away (synchronously)
catalog diff is shipped to every subscribing node synchronously and is kept in memory by the vertica process.
Its only persisted to S3 every five min for durability.
i.e. a DML change is visible as per database transaction semantics. i.e. as soon as its committed.
in the event of a node loss, it might not get synced to disk for persistence, as that happens every 5 min.
i.e. there i no operational impact, there is only impact in cases of disaster or abrupt termination (of ENTIRE primary subcluster)