MongoDB instance with 1 GB cache; workload simple continuously creates collections with the default single _id index.
- At A we begin doing evictions. Dirty fill ratio is small so this appears to be triggered by "bytes allocated for updates" reaching 25 MB or 2.5% of cache. Also disabling
WT-6175eliminates this behavior. Not sure though why this is triggered at 2.5% of cache - isn't the trigger value by default 10%?
- At B it appears we no longer are able to evict the "bytes allocated for updates" and begin indefinitely burning 1 CPU apparently trying to evict content that can't be evicted. This occurs when we reach 6000 collections (12000 tables/files including the single index, 24000 handles). Dropping all the collections reduces open files to 0 but does not immediately reduce handles, and the eviction/cpu behavior continues, so the "bytes allocated for updates" that can't be evicted appears to be associated with handles, not files.
This is related to WT-6420 but distinct from it as it looks like this issue is not specific to very small caches and can happen with any size cache and sufficient file handles.