Allow disabling the MySQL/MariaDB query optimizer for history queries #1219
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I think the config option should be documented. |
| { | ||
| if ($q->getDb()->getAdapter() instanceof Mysql) { | ||
| // Locates the first string column, prepends the optimizer hint, | ||
| // and resets columns to ensure it appears first in the SELECT statement: |
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why the first string column? Does the query hint not work if placed before an (aliased) expression?
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Sure it works, but it will also increase complexity. My thought was that the hint should work (or rather not add crap) for every query scenario, even if it can't be added at all as with SELECT 1 (unaliased expression). Considering that all other queries will select real columns, I decided to use this implementation.
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Aye. But shouldn't it throw an error just in case the first column is not a string? I didn't try, but doubt that this works:
SELECT 1 + 1 as two, /*+ NO_BNL() */ STRAIGHT_JOIN test.name as test_name from test
Some versions of these RDBMS perform poorly with history queries, particularly when the optimizer changes join order or uses block nested loop joins. Ideally, testing across all RDBMS versions to identify when the optimizer fails and adjusting queries or using optimizer switches would be preferable, but this level of effort is not justified at the moment. Optimizer is disabled via config: `/etc/icingaweb2/modules/icingadb/config.ini`: ``` [icingadb] ... disable_optimizer_for_history_queries=1 ```
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| { | ||
| if ($q->getDb()->getAdapter() instanceof Mysql) { | ||
| // Locates the first string column, prepends the optimizer hint, | ||
| // and resets columns to ensure it appears first in the SELECT statement: |
There was a problem hiding this comment.
Aye. But shouldn't it throw an error just in case the first column is not a string? I didn't try, but doubt that this works:
SELECT 1 + 1 as two, /*+ NO_BNL() */ STRAIGHT_JOIN test.name as test_name from test
| */ | ||
| protected static function shouldDisableOptimizerForHistoryQueries(): bool | ||
| { | ||
| return Config::module('icingadb')->get('icingadb', 'disable_optimizer_for_history_queries', false); |
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I think the settings section fits better. There's a doc area for it as well already.
Some versions of these RDBMS perform poorly with history queries, particularly when the optimizer changes join order or uses block nested loop joins. Ideally, testing across all RDBMS versions to identify when the optimizer fails and adjusting queries or using optimizer switches would be preferable, but this level of effort is not justified at the moment.
Optimizer is disabled via config:
/etc/icingaweb2/modules/icingadb/config.ini:refs #1187