[IMPALA-4529] Inefficient use of try/catch in parser

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Fixed
• Affects Version/s: Impala 2.8.0
• Fix Version/s: Impala 2.8.0
• Component/s: Frontend
• Labels: perf
• Target Version: Impala 2.8.0
• Assignee: Tim Armstrong
• Reporter: Tim Armstrong
• Created: 23/Nov/16 21:39
• Updated: 24/Nov/16 08:05
• Resolved: 24/Nov/16 08:05

Description

I was experimenting with some queries with very large case statements and found that the parser was spending a lot of time in this callstack:

"Thread-8" #22 prio=5 os_prio=0 tid=0x0000000009dcc800 nid=0x700f runnable [0x00007f8d95520000]
   java.lang.Thread.State: RUNNABLE
        at java.lang.Integer.parseInt(Integer.java:615)
        at org.apache.impala.analysis.ToSqlUtils.getIdentSql(ToSqlUtils.java:95)
        at org.apache.impala.analysis.ToSqlUtils.getPathSql(ToSqlUtils.java:117)
        at org.apache.impala.analysis.SlotRef.<init>(SlotRef.java:51)
        at org.apache.impala.analysis.CUP$SqlParser$actions.case552(SqlParser.java:13790)
        at org.apache.impala.analysis.CUP$SqlParser$actions.CUP$SqlParser$do_action(SqlParser.java:3828)
        at org.apache.impala.analysis.SqlParser.do_action(SqlParser.java:1228)
        at java_cup.runtime.lr_parser.parse(lr_parser.java:587)
        at org.apache.impala.analysis.AnalysisContext.analyze(AnalysisContext.java:375)
        at org.apache.impala.analysis.AnalysisContext.analyze(AnalysisContext.java:360)
        at org.apache.impala.service.Frontend.analyzeStmt(Frontend.java:891)
        at org.apache.impala.service.Frontend.createExecRequest(Frontend.java:1028)
        at org.apache.impala.service.JniFrontend.createExecRequest(JniFrontend.java:159)

It looks like we're using a try/catch to check if the first character is a digit, which is quite inefficient.