Logical standby performance

Question

Hi,
Will there be any performance impact when using SQL apply logical standby database compared to direct redo apply physical standby database? Let's take we are doing some bulk delete(around 10k) in primary, will there be any more time lag when replicate to LSDB.
Note: Both primary and LSDB are within the same datacenter.
Thanks,
Srini

Answer 1

Hi,
Physical standby works in a simple way – it applies directly (as a recovery would) the changes from the archive log to the respective data blocks. The physical standby typically enjoys smooth and predictable operation. If the physical standby works on a hardware as powerful as the primary’s, it would likely not be a bottleneck.
Logical standby is very different animal altogether!
Not all databases can have LSDB. There are certain data types that are not supported in LSDB (the list depends on the DB version).
To be able to operate reasonably fast, LSDB would require every medium or large table to have primary key (or at least unique index).
Direct insert and parallel DML are not honored by the LSDB.
Batch processes would be processed row-by-row (and get slower as a result of that).
Getting consistently good performance (and no lag) from LSDB requires concerted efforts and cannot be taken for granted even when the LSDB is run on a “primary” hardware.