WalSenderWaitForWAL
Waiting for WAL to be flushed in WAL sender process.
Additional Information​
From the PostgreSQL documentation - Waiting for WAL to be flushed in WAL sender process.
The WalSender process is seen in systems where replication is enabled. The sender process takes the WAL transactions and send them so the replica where the WalReceiver process write the transactions to WAL segments.
Note that the WalSender process is started in response to a request from a replica, so there can be a number of WalSenders running depending on the number of replicas.
How to reduce this wait​
This is an idle wait and is normal to see.
Additional Links​
PostgreSQL docs - Wait Events of Type Activity
Percona Blog - Setting up Streaming Replication
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