[PHOENIX-3023] Slow performance when limit queries are executed in parallel by default

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.8.0
• Fix Version/s: 4.8.0
• Assignee: Samarth Jain
• Reporter: Mujtaba Chohan
• Created: 22/Jun/16 18:19
• Updated: 11/Aug/16 08:27
• Resolved: 27/Jun/16 17:12

Description

After this commit, limit queries are executed in parallel which causes performance to be ~5-10x slower. Providing a serial hint fixes it though.

After commit:

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

Before commit:

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

Test was done on a single node machine running HBase 0.98.17. DDL used was

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