Hello Tim Armstrong, Csaba Ringhofer, I'd like you to reexamine a change. Please visit
http://gerrit.cloudera.org:8080/9943 to look at the new patch set (#13). Change subject: IMPALA-5706: Spilling sort optimisations ...................................................................... IMPALA-5706: Spilling sort optimisations This patch covers multiple changes with the purpose of optimizing spilling sort mechanism: - Remove the hard-coded maximum limit of buffers that can be used for merging the sorted runs. Instead this number is calculated based on the available memory through buffer pool. - The already sorted runs are distributed more optimally between the last intermediate merge and the final merge to avoid that a heavy intermediate merge is followed by a light final merge. - Right before starting the merging phase Sorter tries to allocate additional memory through the buffer pool. - An output run is not allocated anymore for the final merge. Note, double-buffering the runs during a merge was also planned with this patch. However, performance testing showed that except some exotic queries with unreasonably small amount of buffer pool memory available double-buffering doesn't add to the overall performance. It's basically because the half of the available buffers have to be sacrificed to do double-buffering and as a result the merge tree can get deeper. In addition the amount of I/O wait time is not reaching the level where double-buffering could countervail the reduced number of runs during a particular merge. Performance measurements were made during manual testing to verify that this is in fact an optimization: - In case doing a sort on top of a join when working with a restricted amount of memory then the Sort node successfully allocates additional memory right before the merging phase. This is feasible because once Join finishes sending new input data and calls InputDone() then it releases memory that can be picked up by the Sorter. This results in shallower merging trees (more runs grabbed for a merge). - On a multi-node cluster I verified that in cases when at least one merging step is done then this change reduces the execution time for sorts. - The more merging steps are done the bigger the performance gain is compared to the baseline. Change-Id: I74857c1694802e81f1cfc765d2b4e8bc644387f9 --- M be/src/runtime/sorter.cc M be/src/runtime/sorter.h M tests/query_test/test_sort.py 3 files changed, 149 insertions(+), 114 deletions(-) git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/43/9943/13 -- To view, visit http://gerrit.cloudera.org:8080/9943 To unsubscribe, visit http://gerrit.cloudera.org:8080/settings Gerrit-Project: Impala-ASF Gerrit-Branch: master Gerrit-MessageType: newpatchset Gerrit-Change-Id: I74857c1694802e81f1cfc765d2b4e8bc644387f9 Gerrit-Change-Number: 9943 Gerrit-PatchSet: 13 Gerrit-Owner: Gabor Kaszab <gaborkas...@cloudera.com> Gerrit-Reviewer: Csaba Ringhofer <csringho...@cloudera.com> Gerrit-Reviewer: Gabor Kaszab <gaborkas...@cloudera.com> Gerrit-Reviewer: Tim Armstrong <tarmstr...@cloudera.com>