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Type: Task
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Resolution: Unresolved
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Priority: Major - P3
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None
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Affects Version/s: None
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Component/s: None
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Catalog and Routing
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2
The serverStatus command and the FTDC data files report general statistics on the server. As part of this, there is a section dedicated to the Catalog Cache:
shardingStatistics : { ... catalogCache : { numDatabaseEntries : Long("<num>"), numCollectionEntries : Long("<num>"), countStaleConfigErrors : Long("<num>"), totalRefreshWaitTimeMicros : Long("<num>"), numActiveIncrementalRefreshes : Long("<num>"), countIncrementalRefreshesStarted : Long("<num>"), numActiveFullRefreshes : Long("<num>"), countFullRefreshesStarted : Long("<num>"), countFailedRefreshes : Long("<num>") } ... }
In case of the FTDC file, this information can be graphically represented by T2:
One goal of this ticket is to identify metrics that can be considered useful and clear for investigating the behavior of the Catalog Cache (i.e., it shouldn't need to be a Sharding expert to interpreter these metrics).
Ideally, for both collection and database metadata, we would need (TBD):
- number of the entries in the cache (TBD: stale and non-stale?)
- number of cache misses (TBD: and cache hits?)
- number of incremental refreshes started/completed (only for collection metadata)
- number of full refreshes started/completed
- number of failed refreshes
- time spent waiting for refreshes (in milliseconds)
On the other hand, T2 should be fixed and/or improved to represent this information in the best way (for example, it currently shows threads as unit of the totalRefreshWaitTimeMicros metric, which is a definitely a bug). Consequently, some tickets for the Server Triage & Release team should be created as a part of this work.
- is depended on by
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SERVER-80724 Add database refresh statistics to Catalog Cache
- Blocked
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SERVER-80868 Complete TODO listed in SERVER-34164
- Blocked
- is related to
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SERVER-34164 [support] add stats for database refresh to CatalogCache
- Closed