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  1. MariaDB Server
  2. MDEV-9271

Asynchronous userstat





      In optimized environments, especially when there are many small queries running consequentially, statistics is really giving a visible slowdown.

      This is my typical situation (performance schema off; slowlog off; userstat = 1):

      starting 0.000073
      Waiting for query cache lock 0.000020
      init 0.000023
      checking query cache for query 0.000074
      checking permissions 0.000021
      checking permissions 0.000017
      checking permissions 0.000017
      Opening tables 0.000070
      After opening tables 0.000023
      System lock 0.000019
      Table lock 0.000018
      After opening tables 0.000018
      Waiting for query cache lock 0.000017
      After opening tables 0.000040
      init 0.000068
      optimizing 0.000045
      statistics 0.001257
      preparing 0.000135
      executing 0.000023
      Sending data 0.000278
      Waiting for query cache lock 0.000023
      Sending data 0.000214
      end 0.000022
      query end 0.000016
      closing tables 0.000031
      freeing items 0.000021
      updating status 0.000016
      Waiting for query cache lock 0.000014
      updating status 0.000023
      Waiting for query cache lock 0.000026
      updating status 0.000016
      storing result in query cache 0.000021
      cleaning up 0.000018

      To cut long story short - 58% of time is used for "Statistics" (1.3 milliseconds in this particular query). It's not consistent. Sometimes it's about 30%. But basically varies from 30% to 80%. I understood that it's still fast, but sometimes there are 10,000 queries per page or per second and statistics then can waste 10 seconds per page load (in very bad optimized website, well).

      I am thinking that user statistics is something that have no need to be done synchronously (blocking returning "DONE" state to client). I mean, that, could be awesome to do such logic:

      execute query
      return result "query DONE" so client can continue with other queries
      asynchronously write new row to "statistics buffer"
      later (asynchronously) add new rows from "statistics buffer" to "statistics table"




            Unassigned Unassigned
            Profforg Alexander Loginov
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