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From "Philip Zeyliger (Code Review)" <ger...@cloudera.org>
Subject [Impala-ASF-CR] IMPALA-5243: Speed up code gen for wide Avro tables.
Date Sun, 22 Oct 2017 04:09:00 GMT
Hello Tim Armstrong, 

I'd like you to reexamine a change. Please visit

    http://gerrit.cloudera.org:8080/8211

to look at the new patch set (#4).

Change subject: IMPALA-5243: Speed up code gen for wide Avro tables.
......................................................................

IMPALA-5243: Speed up code gen for wide Avro tables.

HdfsAvroScanner::CodegenMaterializeTuple generates a function linear in
size to the number of columns. On 1000 column tables, codegen time is
significant. This commit roughly halves it for wide columns.
(Note that this had been much worse in recent history (<= Impala 2.9).)

It does so by breaking up MaterializeTuple() into multiple smaller
functions, and then calls them in order. When breaking up into
200-column chunks, there is a noticeable speed-up.

I've made the helper code for generating LLVM function prototypes
have a mutable function name, so that the builder can be re-used
multiple times.

I've checked by inspecting optimized LLVM that in the case where there's
only 1 helper function, code gets inlined so that there doesn't seem to
be an extra function.

I measured codegen time for various "step sizes." The case where there
are no helper functions is about 2.7s. The best case was about a step
size of 200, with timings of 1.3s.

For the query "select count(int_col16) from functional_avro.widetable_1000_cols",
codegen times as a function of step size are roughly as follows. This is
averaged across 5 executions, and rounded to 0.1s.

   step time
     10	2.4
     50	2.5
     75	2.9
    100	3.0
    125	3.0
    150	1.4
    175	1.3
    200	1.3 <-- chosen step size
    225	1.5
    250	1.4
    300	1.6
    400	1.6
    500	1.8
   1000	2.7

The raw data was generated like so, with some code that let me change the step size at runtime:

  $(for step in 10 50 75 100 125 150 175 200 225 250 300 400 500 1000; do for try in $(seq
5); do echo $step > /tmp/step_size.txt; echo -n "$step "; impala-shell.sh -q "select count(int_col16)
from functional_avro.widetable_1000_cols; profile;" 2> /dev/null | grep -A9 'CodeGen:(Total:
[0-9]*s' -m 1 | sed -e 's/ - / /' |
  sed -e 's/([0-9]*)//' | tr -d '\n' | tr -s ' ' ' '; echo; done; done) | tee out.txt
  ...
  200  CodeGen:(Total: 1s333ms, non-child: 1s333ms, % non-child: 100.00%) CodegenTime: 613.562us
CompileTime: 605.320ms LoadTime: 0.000ns ModuleBitcodeSize: 1.95 MB NumFunctions: 38 NumInstructions:
8.44K OptimizationTime: 701.276ms PeakMemoryUsage: 4.12 MB PrepareTime: 10.014ms
  ...
  1000  CodeGen:(Total: 2s659ms, non-child: 2s659ms, % non-child: 100.00%) CodegenTime: 558.860us
CompileTime: 1s267ms LoadTime: 0.000ns ModuleBitcodeSize: 1.95 MB NumFunctions: 34 NumInstructions:
8.41K OptimizationTime: 1s362ms PeakMemoryUsage: 4.11 MB PrepareTime: 10.574ms

I have run the core tests with this change.

Change-Id: I7f1b390be4adf6e6699a18344234f8ff7ee74476
---
M be/src/codegen/llvm-codegen.h
M be/src/exec/hdfs-avro-scanner.cc
M be/src/exec/hdfs-avro-scanner.h
3 files changed, 156 insertions(+), 100 deletions(-)


  git pull ssh://gerrit.cloudera.org:29418/Impala-ASF refs/changes/11/8211/4
-- 
To view, visit http://gerrit.cloudera.org:8080/8211
To unsubscribe, visit http://gerrit.cloudera.org:8080/settings

Gerrit-Project: Impala-ASF
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: I7f1b390be4adf6e6699a18344234f8ff7ee74476
Gerrit-Change-Number: 8211
Gerrit-PatchSet: 4
Gerrit-Owner: Philip Zeyliger <philip@cloudera.com>
Gerrit-Reviewer: Philip Zeyliger <philip@cloudera.com>
Gerrit-Reviewer: Tim Armstrong <tarmstrong@cloudera.com>

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