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MichaelGorsich
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Centera Query Fetches at Highly Variable Rate

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Running a query multiple times with a result set of about 2,500 Clips, Centera Query will sometimes:

¤ Fetch a few, then pause a few minutes, then fetch the remaining clips in under a second

¤ Timeout (after ten 50 second timeouts) )

¤ Wait a few minutes (three to five 50 second timeouts), then fetch all at once in under a second

Isn't Centera query supposed to return results as it gets them?  If it would send the results as it finds them I wouldn't get unnecessary timeouts

SDK: 3.1.544 (due to running on Win2003)

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mfh2
2 Iron

Re: Centera Query Fetches at Highly Variable Rate

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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

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mfh2
2 Iron

Re: Centera Query Fetches at Highly Variable Rate

Jump to solution

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

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