Send queues and receive queues

Enterprise Replication uses send and receive queues to receive and deliver replication data to and from database servers that participate in a replicate.

Send queue

Enterprise Replication stores replication data in memory to be delivered to target database servers that participate in a replicate. If the send queue fills, Enterprise Replication spools the send-queue transaction records to a dbspace and the send-queue row data to an sbspace.

Receive queue

Enterprise Replication stores replication data in memory at the target database server until the target database server acknowledges receipt of the data. If the receive queue fills as a result of a large transaction, Enterprise Replication spools the receive queue transaction header and replicate records to a dbspace and the receive queue row data to an sbspace.

The data contains the filtered log records for a single transaction. Enterprise Replication stores the replication data in a stable (recoverable) send queue on the source database server. Target sites acknowledge receipt of data when it is applied to or rejected from the target database.

If a target database server is unreachable, the replication data remains in a stable queue at the source database server. Temporary failures are common, and no immediate action is taken by the source database server; it continues to queue transactions. When the target database server becomes available again, queued transactions are transmitted and applied.

If the target database server is unavailable for an extended period, the send queue on the source database server might use excessive resources. In this situation, you might not want to save all transactions for the target database server. To prevent unlimited transaction accumulation, you can remove the unavailable target database server from the replicate. Before the database server that is removed rejoins any replicate, however, you must synchronize (bring tables to consistency) with the other database servers.