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Bug #9691

closed

fat zap should prefetch when iterating

Added by Brad Lewis almost 4 years ago. Updated over 3 years ago.

Status:
Closed
Priority:
Normal
Assignee:
Category:
-
Start date:
2018-08-01
Due date:
% Done:

100%

Estimated time:
Difficulty:
Medium
Tags:
needs-triage
Gerrit CR:

Description

When iterating over a ZAP object, we're almost always certain to iterate over the entire object. If there are multiple leaf blocks, we can realize a performance win by issuing reads for all the leaf blocks in parallel when the iteration begins.

For example, if we have 10,000 snapshots, "zfs destroy -nv pool/fs@1%9999" can take 30 minutes when the cache is cold. This change provides a >3x performance improvement, by issuing the reads for all ~64 blocks of each ZAP object in parallel.

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