[jira] [Commented] (TS-2536) Performance improvements to VariableExpander in header_rewrite

["Leif Hedstrom (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/TS-2536?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13883448#comment-13883448 ] 

Leif Hedstrom commented on TS-2536:
-----------------------------------

TS-2501 implements some improvements to short cut the (many) cases where the variable expansion is unecessary. But I feel there's room for future improvements here, so filing this.

> Performance improvements to VariableExpander in header_rewrite
> --------------------------------------------------------------
>
>                 Key: TS-2536
>                 URL: https://issues.apache.org/jira/browse/TS-2536
>             Project: Traffic Server
>          Issue Type: Bug
>          Components: Plugins
>            Reporter: Leif Hedstrom
>             Fix For: sometime
>
>
> It seems that VariableExpander gets instantiated and executed on every add-header operator. However, this seems rather suboptimal for a number of reasons:
> 1. It might not even be necessary (i.e. there might not be any %<> strings in the "static" string.
> 2. Perhaps even more important, we look for these strings on every request, even though if they are there, they would always be in the same position on every request.
> One suggestion would be to incorporate the VariableExpander "state" as part of parsing the configuration on startup / reload. Maybe it gets complicated when there are other expansions, but it still feels we can pre-parse these strings and get some ideas of what needs to be expanded once, and not on every request.
> This is similar to how e.g. the regex_remap plugin works, it recalculates the positions and expansion once only.
> Thoughts?



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