[wp-trac] [WordPress Trac] #55463: Add a limit to _prime_*_cache functions

[WordPress Trac]

#55463: Add a limit to _prime_*_cache functions
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 Reporter:  spacedmonkey                         |       Owner:
                                                 |  spacedmonkey
     Type:  enhancement                          |      Status:  assigned
 Priority:  normal                               |   Milestone:  Future
                                                 |  Release
Component:  Cache API                            |     Version:
 Severity:  normal                               |  Resolution:
 Keywords:  good-first-bug has-patch 2nd-        |     Focuses:
  opinion                                        |  performance
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Changes (by soulseekah):

 * keywords:  good-first-bug has-patch => good-first-bug has-patch 2nd-
               opinion


Comment:

 I was unable to reproduce any difference between having a limit and not
 having a limit whatsoever.

 The query planner (EXPLAIN) and the query trace
 (information_schema.OPTIMIZER_TRACE) are absolutely the same, apart from
 the `rows_estimation` step in the `join_optimization`, where the
 `range_analysis` `table_scan` estimated cost is actually higher (even
 though the range scan is not performed) for a query with a LIMIT clause.

 See screenshot above.

 Any benchmarks done using mictrotime inside PHP itself will vary wildly
 depending on kernel scheduling (other tasks running), if you run the two
 versions over 6-12 hours on an idle machine (preferably bare-metal
 hardware, as VPS's tend to be noisy as well) the results should converge.

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Ticket URL: <https://core.trac.wordpress.org/ticket/55463#comment:9>
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