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Ryan Lyu
Ryan Lyu

Reputation: 5125

AWS RDS: why is there "write IOPS" in my replica instance?

The following is a PostgreSQL replica instance. I have no idea why there is write IOPS in my dashboard.

From my understanding, only read happens in replica instance.

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Upvotes: 2

Views: 1531

Answers (2)

Parsifal
Parsifal

Reputation: 4486

A Postgres database replica contains all of the data storage (tablespaces and other internally-managed files) that are present on the primary instance. The difference is that these data files are updated based on information in the write-ahead log (WAL) rather than user-submitted inserts/updates/deletes.

In addition, as a commenter noted, Postgres also uses temporary tables that may be flushed to disk, even for read-only queries.

In practice, you will need at least as many total IOPS for your replicas as you need for the primary, because the replica will typically be performing IO-intensive queries in addition to the updates received from the primary.

Upvotes: 0

Chris Williams
Chris Williams

Reputation: 35146

You still have writes from the master node as data is replicated.

Additionally any interactions that use temp tables would perform a local write to disk.

Upvotes: 3

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