Mujtaba Chohan created PHOENIX-3023:
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Summary: Slow performance when limit queries are executed in
parallel by default
Key: PHOENIX-3023
URL: https://issues.apache.org/jira/browse/PHOENIX-3023
Project: Phoenix
Issue Type: Bug
Reporter: Mujtaba Chohan
After
[this|https://git-wip-us.apache.org/repos/asf?p=phoenix.git;a=commit;h=54362430d71be788d515944573572624628a09b6]
commit, limit queries are executed in parallel which causes performance to be
~5-10x slower. Providing a serial hint fixes it though.
After commit:
{code}
select * from WIDE_PK order by mypk DESC limit 1; // this takes ~400ms
CLIENT 1280-CHUNK 1996304 ROWS 6380181208 BYTES PARALLEL 4-WAY REVERSE FULL
SCAN OVER WIDE_PK SERVER 1 ROW LIMIT CLIENT MERGE SORT CLIENT 1 ROW LIMIT
{code}
Before commit:
{code}
select * from WIDE_PK order by mypk DESC limit 1; // this takes ~40ms
CLIENT 1280-CHUNK 1996304 ROWS 6380181208 BYTES SERIAL 4-WAY REVERSE FULL SCAN
OVER WIDE_PK SERVER 1 ROW LIMIT CLIENT MERGE SORT CLIENT 1 ROW LIMIT
{code}
Test was done on a single node machine running HBase 0.98.17. DDL used was
{code}CREATE TABLE WIDE_PK (MYPK CHAR(500) NOT NULL PRIMARY KEY,CF.column1
INTEGER,CF.column2 INTEGER,CF.column3 INTEGER,CF.column4 INTEGER,CF.column5
INTEGER) SALT_BUCKETS=4 with phoenix.stats.guidepost.width of 5000000
{code}
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