Re: jsonpath

On Wed, Apr 17, 2019 at 8:43 PM Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> John Naylor <john(dot)naylor(at)2ndquadrant(dot)com> writes:
> > Attached is a patch to fix some minor issues:
> > -misspelling of an error message
>
> Yeah, I'd noticed that one too :-(. I think the whole jsonpath patch
> needs a sweep to bring its error messages into line with our style
> guidelines, but no harm in starting with the obvious bugs.

I'll go trough the jsonpath error messages and post a patch for fixing them.

> > -Commit 550b9d26f80f failed to update the Makefile comment to reflect
> > how the build changed, and also removed the clean target, which we now
> > have use for since we later got rid of backtracking in the scanner.
>
> Right. I'm not really sure why we're bothering with anti-backtracking
> here, or with using speed-rather-than-code-space lexer optimization
> options. It's hard for me to credit that any practically-useful jsonpath
> pattern would be long enough for lexer speed to matter, and even harder to
> credit that the speed of the flex code itself would be an important factor
> in the overall processing cost of a long jsonpath. Still, as long as we
> have the code it needs to be right.

Actually I found that non of in-core lexers are backtracking. So, I
understood no backtracking as kind of standard and didn't want to
break that :)

Nevertheless, I could imagine use-case involving parsing a lot of
jsonpath'es. For example we may construct jsonpath based on table
data and check that for just few jsonb's. For sure, that wouldn't be
a common use-case, but still.

> > Also, while I have the thought in my head, for v13 we should consider
> > replacing the keyword binary search with the perfect hash technique
> > added in c64d0cd5ce2 -- it might give a small performance boost to the
> > scanner.
>
> I doubt it's worth the trouble, per above.
>
> Patch LGTM, pushed.

Thank you for pushing this!

------
Alexander Korotkov
Postgres Professional: http://www.postgrespro.com
The Russian Postgres Company