The Centera query operation has semantics that require results to be returned in a strict time ordering (oldest first, by write timestamp). This means the results have to be gathered from all the storage nodes in a broadcast request and then the results are ordered by the coordinating access node before they get passed back to your client. The access node has to wait for all of the storage nodes to start streaming results before it can return anything; the amount of time a particular storage node takes to process a query request depends on what else it is being asked to do at the time.
All of this adds up to unpredictable query result performance. Luckily, query is not an operation that is typically required for day-to-day operation of a Centera application - it is mostly there for DR purposes.
mfh2
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March 20th, 2015 11:00
Hi Michael -
The Centera query operation has semantics that require results to be returned in a strict time ordering (oldest first, by write timestamp). This means the results have to be gathered from all the storage nodes in a broadcast request and then the results are ordered by the coordinating access node before they get passed back to your client. The access node has to wait for all of the storage nodes to start streaming results before it can return anything; the amount of time a particular storage node takes to process a query request depends on what else it is being asked to do at the time.
All of this adds up to unpredictable query result performance. Luckily, query is not an operation that is typically required for day-to-day operation of a Centera application - it is mostly there for DR purposes.
Best Regards,
Mike Horgan