March 6, 2007 at 4:52 pm
Hi,
Have anyone been using database mirroring on SQL 2005 Server Standard Edition? It says the edition can only have synchronous mirroring with safety option set "ON" (the same as FULL?):
"Single REDO thread and the safety setting is always on."
Is there much of performance hit having such option on? What will happen if the target server becomes unavailable or responds slowly? Will the primary production system get blocked until the log is applied on the target server?
"If transaction safety (or just 'safety') is set to FULL, the principal and mirror servers operate in a synchronous transfer mode. As the principal server hardens its principal database log records to disk, it also sends them to the mirror. The principal then waits for a response from the mirror server. The mirror responds when it has hardened those same log records to the mirror's log disk. When safety is set OFF, the principal does not wait for acknowledgment from the mirror, and so the principal and mirror may not be fully synchronized (that is, the mirror may not quite keep up with the principal)."
Will appreciate any ideas.
Thanks.
March 7, 2007 at 1:56 pm
I think the biggest hit performance-wise is with large/long transactions (index rebuilds etc) If the target can't keep up with the workload, thats what the REDO queue is for.. it will build as the target falls behind.. The faster your connection/hardware is, the quicker that will dissipate.
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