[SERVER-18081] Tailing the oplog requires paging in the recently added entries under WiredTiger Created: 16/Apr/15  Updated: 06/Dec/22  Resolved: 21/Dec/16

Status: Closed
Project: Core Server
Component/s: WiredTiger
Affects Version/s: 3.0.1
Fix Version/s: None

Type: Bug Priority: Major - P3
Reporter: Bruce Lucas (Inactive) Assignee: Backlog - Storage Execution Team
Resolution: Duplicate Votes: 0
Labels: WTcc
Remaining Estimate: Not Specified
Time Spent: Not Specified
Original Estimate: Not Specified

Issue Links:
Duplicate
duplicates SERVER-23622 Inconsistent throughput during insert... Closed
Related
related to SERVER-23622 Inconsistent throughput during insert... Closed
related to SERVER-26988 Secondary delay causes large drop in ... Closed
related to WT-2647 Improve page-out behavior for OpLog Closed
is related to SERVER-18079 Large performance drop with documents... Closed
Assigned Teams:
Storage Execution
Backwards Compatibility: Fully Compatible
Operating System: ALL
Participants:

 Description   

While debugging a large performance drop related to the oplog filling (see SERVER-18079 for details) I noticed that the issue was exacerbated by the fact that the thread tailing the oplog is having to page in the recently added entries at the end of the oplog (see these stack traces from that ticket).

Independent of the memory allocator issues on that ticket, it seems that having to page in the recently added oplog entries is not optimal for performance. Is there any way to avoid this?



 Comments   
Comment by Daniel Pasette (Inactive) [ 08/Jun/15 ]

The actual impact needs to be quantified, but this may be important for primary performance. Most likely to happen when tailing the oplog falls slightly behind, ie, > 10M behind when splits/evictions kick in. Need to pay attention to cache misses on the oplog collection. Keep in mind that truncation at the beginning of the oplog may also cause cache misses.

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