Re: Rethinking MemoryContext creation

On 12/11/2017 05:27 PM, Tom Lane wrote:
> I wrote:
>> While fooling around with a different problem, I got annoyed at how slow
>> MemoryContext creation and deletion is.
>
> Looking at this some more, there's another micro-optimization we could
> make, which is to try to get rid of the strlen+strcpy operations needed
> for the context name. (And yes, I'm seeing those show up in profiles,
> to the tune of a couple percent of total runtime in some examples.)
>
> For a *very* large majority of the callers of AllocSetContextCreate,
> the context name is a simple C string constant, so we could just store
> the pointer to it and save the space and cycles required to copy it.
> This would require providing a separate API for the few callers that are
> actually passing transient strings, but that's easy enough. I envision
> AllocSetContextCreate becoming a wrapper macro for
> "AllocSetContextCreateExtended", which'd take a flag argument specifying
> whether the context name needs to be copied.
>
> However, unless we want to run around and touch all the ~ 150 calls
> with constant arguments, we'd have to set things up so that the default
> behavior for AllocSetContextCreate is to not copy. This risks breaking
> callers in extensions. Not entirely sure if it's worth that --- any
> thoughts?
>

I don't think silently breaking extensions is particularly attractive
option, so I guess we'll have to run around and tweak the ~150 calls.

regards

--
Tomas Vondra http://www.2ndQuadrant.com
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