Fix the sampling of the pgsa query #255
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It wrongly computes the sampling: the "total" column is not correct in this context: we (most of the time) have more than 1 record per sample. If you have 100 sessions, the sampling will be off by a factor of 100, and you'll end up with only 1 sample It's a bit ugly to fix, because we need another subquery... Closes #254
rjuju
requested changes
Feb 8, 2025
| @@ -517,9 +517,9 @@ def BASE_QUERY_PGSA_SAMPLE(per_db=False): | |||
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| # We use dense_rank() as we need ALL the records for a specific ts | |||
| return """ | |||
| (SELECT *,max(number) OVER () AS total FROM | |||
| (SELECT pgsa_history.srvid, | |||
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could you indent this as this is now a sub query?
| @@ -546,7 +546,7 @@ def BASE_QUERY_PGSA_SAMPLE(per_db=False): | |||
| AND pgsac.srvid = %(server)s | |||
| ) AS pgsa_history | |||
| {extra} | |||
| ) AS pgsa | |||
| ) AS temp) AS pgsa | |||
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nit: ideally we should avoid keywords here even if that seems to be allowed. maybe just tmp or something
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yeah the need for a sub query is annoying. For the record some other db like duckdb now support a QUALIFY clause (https://duckdb.org/docs/sql/query_syntax/qualify.html) which fixes that problems. I implemented a prototype for postgres some months ago but never sent it. It's not part of the standard so I don't think it will be accepted. |
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It wrongly computes the sampling: the "total" column is not correct in this context: we (most of the time) have more than 1 record per sample. If you have 100 sessions, the sampling will be off by a factor of 100, and you'll end up with only 1 sample
It's a bit ugly to fix, because we need another subquery...
Closes #254