GBM/DRF: Remove redundant extraction weights in histogram

[exalate-issue-sync]

Speed-up GBM&DRF by avoiding unnecessary work.

This is done once at the beginning and is thus redundant, the removed line does it for every column - concurrently!!! - that can be very bad for performance because different threads are writing to the same shared array.

Timings master vs fix on redhat dataset with gbm-noscoring benchmark configuration with 5 fold cross-validation:
(seconds)

master.jar-1, 326.3
master.jar-2, 326.3
master.jar-3, 325.2
master.jar-4, 326.2
master.jar-5, 326.1
michalk_weights-fix.jar-1, 281
michalk_weights-fix.jar-2, 283.9
michalk_weights-fix.jar-3, 278.7
michalk_weights-fix.jar-4, 278.7
michalk_weights-fix.jar-5, 279.2
We see about 12% speed-up.

[h2o-ops]

JIRA Issue Details

Jira Issue: PUBDEV-8060
Assignee: Michal Kurka
Reporter: Michal Kurka
State: Resolved
Fix Version: 3.32.1.1
Attachments: N/A
Development PRs: Available

[h2o-ops]

Linked PRs from JIRA

#5337