Latency is the time it takes for the data to replicate at the subscriber once it updates the primary.

Reason for latency

1. When DSI thread is down
2. When huge batch jobs running on the primary database.
3. When blocking at replicate database
4. When replicate database log is full
5. When stats are not up to date on replicate database
6. In some cases it may happen that source table is having index created on it, but it does not exists on target database, this can causing latency.

For most logical replication (ie. SQL Server or Sybase Rep Server) is throughput to the target server. For Sybase, that is the DSI thread. If you update 10,000 rows in the source server and they replicate as individual updates into the target server, that is one statement being replicated as 10,000 replication statements. The processing to go get the on-disk data pages for each individual update can take time as does the compilation of those 10,000 statements.

If you replicate with Sybase, use the statement cache and literal autoparm options on the targets such that the compilation of the statements does not occur. It can be a HUGE benefit to DSI throughput to the target.