perf(sql): improve performance of cross joins#5741
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bluestreak01 merged 23 commits intomasterfrom Jul 4, 2025
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core/src/main/java/io/questdb/griffin/engine/groupby/DistinctRecordCursorFactory.java
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core/src/main/java/io/questdb/griffin/engine/groupby/DistinctRecordCursorFactory.java
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please fix the bug in the distinct cursor and symbol columns. others things are not critical.
also: do you have a query + schema this is aiming to improve? I don't want to invent my own to test it.
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thanks @jerrinot 👍 this was the trigger: WITH
curr_usd_data AS (
SELECT count(*) as symbol, sum(price)
FROM trades
WHERE side='buy'
)
SELECT dateadd('m', x::int, '2024-11-13T11:00:00.000000Z'::timestamp) AS send_ts, 'USD' as sym, 1.0 AS usd_rate, symbol
FROM long_sequence(60)
CROSS JOIN curr_usd_data; |
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[PR Coverage check]😍 pass : 204 / 235 (86.81%) file detail
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Background
Cross joins are in active production use. They rely heavily on
RecordCursor.toTop()to be a lightweight operation to restart the cursor. Cross join will restart the secondary cursor for every row of the primary. Some of our cursor implementations are unnecessarily heavy to restart. Such asselect count() ....Implementation
I introduced an abstract method that is meant to compute the hash of the "heavy" state of the cursor. For example, "mapIsBuilt" boolean field is used as input to this hash. If toTop() changes the value of this field - hash will change too.
assertQuery()exercisestopTop()and asserts that this hash does not change before and aftertoTopcall.Details
toTop()does not discard cursor's state where this state was pre-builtImportant