Aleksandr Efimov has posted comments on this change. ( http://gerrit.cloudera.org:8080/24896 )
Change subject: IMPALA-15381: Reduce reservoir RNG state ...................................................................... Patch Set 3: Thanks for trying it. The gain is per group, not per row, so HistogramTest (7 groups at the 20000-sample cap) is exactly the case where nothing changes. Lab cluster, 3 nodes, tpch_parquet.lineitem SF1, debug build, so the times are only good relative to each other: appx_median(l_shipmode) ... group by l_orderkey, 1.5M groups of ~4 rows: 4653 -> 598 bytes per group outside the reservation, 5.32GB -> 346MB of intermediate rows into the merge, and 5.3-5.9s -> 1.71-1.76s per query. Grouped by l_shipmode instead, 7 groups at the cap: unchanged, like HistogramTest. mt19937_64 seeds 312 words per group in the constructor, and the whole state goes into every serialized intermediate row. -- To view, visit http://gerrit.cloudera.org:8080/24896 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: Impala-ASF Gerrit-Branch: master Gerrit-MessageType: comment Gerrit-Change-Id: I9e046e3f0c1b91f1761ce578601a330bd864eb84 Gerrit-Change-Number: 24896 Gerrit-PatchSet: 3 Gerrit-Owner: Aleksandr Efimov <[email protected]> Gerrit-Reviewer: Aleksandr Efimov <[email protected]> Gerrit-Reviewer: Csaba Ringhofer <[email protected]> Gerrit-Reviewer: Impala Public Jenkins <[email protected]> Gerrit-Reviewer: Joe McDonnell <[email protected]> Gerrit-Reviewer: Michael Smith <[email protected]> Gerrit-Reviewer: Riza Suminto <[email protected]> Gerrit-Comment-Date: Tue, 22 Sep 2026 18:11:07 +0000 Gerrit-HasComments: No
