[ https://issues.apache.org/jira/browse/IMPALA-8203?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Work on IMPALA-8203 started by Alex Rodoni. ------------------------------------------- > Revisit disable_codegen docs > ---------------------------- > > Key: IMPALA-8203 > URL: https://issues.apache.org/jira/browse/IMPALA-8203 > Project: IMPALA > Issue Type: Improvement > Components: Docs > Affects Versions: Impala 3.1.0 > Reporter: Tim Armstrong > Assignee: Alex Rodoni > Priority: Minor > > This text is confusing in various ways, someone pointed out to me. > * We don't need to specifically reference crashes - mostly it's used as a > workaround for performance problems. I think we should just say that it's > used to work around any issues with Impala's runtime code generation. > * We should say clearly that most queries will run significantly slower with > DISABLE_CODEGEN=true. The current text says this but it's hard to parse > because of the implied double negative "do not run with the setting turned > on", where "turned on" means "not disabled". > * It's still worth mentioning that some short-running queries may run faster > with DISABLE_CODEGEN=true because of the overhead, but we shouldn't actively > suggest users to tweak it in general. In 2.10+, the > DISABLE_CODEGEN_ROWS_THRESHOLD optimisation automatically disables codegen > for small queries to solve this automatically. > {noformat} > DISABLE_CODEGEN Query Option > This is a debug option, intended for diagnosing and working around issues > that cause crashes. If a query fails with an "illegal instruction" or other > hardware-specific message, try setting DISABLE_CODEGEN=true and running the > query again. If the query succeeds only when the DISABLE_CODEGEN option is > turned on, submit the problem to <support channel> and include that detail in > the problem report. Do not otherwise run with this setting turned on, because > it results in lower overall performance. > Because the code generation phase adds a small amount of overhead for each > query, you might turn on the DISABLE_CODEGEN option to achieve maximum > throughput when running many short-lived queries against small tables. > Type: Boolean; recognized values are 1 and 0, or true and false; any other > value interpreted as false > Default: false (shown as 0 in output of SET statement) > {noformat} -- This message was sent by Atlassian JIRA (v7.6.3#76005) --------------------------------------------------------------------- To unsubscribe, e-mail: issues-all-unsubscr...@impala.apache.org For additional commands, e-mail: issues-all-h...@impala.apache.org