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  • create-index should run analyze after creating index · 6 ✖
id html_url issue_url node_id user created_at updated_at ▲ author_association body reactions issue performed_via_github_app
1008166084 https://github.com/simonw/sqlite-utils/issues/365#issuecomment-1008166084 https://api.github.com/repos/simonw/sqlite-utils/issues/365 IC_kwDOCGYnMM48F2TE fgregg 536941 2022-01-08T22:32:47Z 2022-01-08T22:32:47Z CONTRIBUTOR

or using “ pragma optimize”

 
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 create-index should run analyze after creating index 1096558279  
1008164786 https://github.com/simonw/sqlite-utils/issues/365#issuecomment-1008164786 https://api.github.com/repos/simonw/sqlite-utils/issues/365 IC_kwDOCGYnMM48F1-y fgregg 536941 2022-01-08T22:24:19Z 2022-01-08T22:24:19Z CONTRIBUTOR

the out-of-date scenario you describe could be addressed by automatically adding an analyze to the insert or convert commands if they implicate an index

 
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 create-index should run analyze after creating index 1096558279  
1008164116 https://github.com/simonw/sqlite-utils/issues/365#issuecomment-1008164116 https://api.github.com/repos/simonw/sqlite-utils/issues/365 IC_kwDOCGYnMM48F10U fgregg 536941 2022-01-08T22:18:57Z 2022-01-08T22:18:57Z CONTRIBUTOR

the table with the query ran so bad was about 50k.

i think the scenario should not be worse than no stats.

i also did not know that sqlite was so different from postgres and needed an explicit analyze call.

 
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 create-index should run analyze after creating index 1096558279  
1008163050 https://github.com/simonw/sqlite-utils/issues/365#issuecomment-1008163050 https://api.github.com/repos/simonw/sqlite-utils/issues/365 IC_kwDOCGYnMM48F1jq simonw 9599 2022-01-08T22:10:51Z 2022-01-08T22:10:51Z OWNER

Is there a downside to having a sqlite_stat1 table if it has wildly incorrect statistics in it?

Imagine the following sequence of events:

  • User imports a few records, creating the table, using sqlite-utils insert
  • User runs sqlite-utils create-index ... which also creates and populates the sqlite_stat1 table
  • User runs insert again to populate several million new records

The user now has a database file with several million records and a statistics table that is wildly out of date, having been populated when they only had a few.

Will this result in surprisingly bad query performance compared to it that statistics table did not exist at all?

If so, I lean much harder towards ANALYZE as a strictly opt-in optimization, maybe with the --analyze option added to sqlite-utils insert top to help users opt in to updating their statistics after running big inserts.

 
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 create-index should run analyze after creating index 1096558279  
1008161965 https://github.com/simonw/sqlite-utils/issues/365#issuecomment-1008161965 https://api.github.com/repos/simonw/sqlite-utils/issues/365 IC_kwDOCGYnMM48F1St fgregg 536941 2022-01-08T22:02:56Z 2022-01-08T22:02:56Z CONTRIBUTOR

for options 2 and 3, i would worry about discoverablity.

in other db’s it is not necessary to explicitly call analyze for most indices. ie for postgres

The system regularly collects statistics on all of a table's columns. Newly-created non-expression indexes can immediately use these statistics to determine an index's usefulness.

i suppose i would propose raising a warning if the stats table is created that explains what is going on and informs users about a —no-analyze argument.

 
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 create-index should run analyze after creating index 1096558279  
1008158357 https://github.com/simonw/sqlite-utils/issues/365#issuecomment-1008158357 https://api.github.com/repos/simonw/sqlite-utils/issues/365 IC_kwDOCGYnMM48F0aV simonw 9599 2022-01-08T21:33:07Z 2022-01-08T21:33:07Z OWNER

The one thing that worries me a little bit about doing this by default is that it adds a surprising new table to the database - it may be confusing to users if they run create-index and their database suddenly has a new sqlite_stat1 table, see https://github.com/simonw/sqlite-utils/issues/366#issuecomment-1008157132

Options here are:

  • Do it anyway. People can tolerate a surprise table appearing when they create an index.
  • Only run ANALYZE if the user says sqlite-utils create-index ... --analyze
  • Use the --analyze option, but also automatically run ANALYZE if they create an index and the database they are working with already has a sqlite_stat1 table

I'm currently leading towards that third option - @fgregg any thoughts?

 
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 create-index should run analyze after creating index 1096558279  

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