Re: [proposal] de-TOAST'ing using a iterator

Hi Thomas,
I've fixed the warnings.

Thomas Munro <thomas.munro@gmail.com> 于2019年7月5日周五 下午12:21写道：

> On Thu, Jun 20, 2019 at 1:51 AM Binguo Bao <djydewang@gmail.com> wrote:
> > Hi hackers!
> > This proposal aims to provide the ability to de-TOAST a fully TOAST'd
> and compressed field using an iterator and then update the appropriate
> parts of the code to use the iterator where possible instead of
> de-TOAST'ing and de-compressing the entire value. Examples where this can
> be helpful include using position() from the beginning of the value, or
> doing a pattern or substring match.
> >
> > de-TOAST iterator overview:
> > 1. The caller requests the slice of the attribute value from the
> de-TOAST iterator.
> > 2. The de-TOAST iterator checks if there is a slice available in the
> output buffer, if there is, return the result directly,
> >     otherwise goto the step3.
> > 3. The de-TOAST iterator checks if there is the slice available in the
> input buffer, if there is, goto step44. Otherwise,
> >     call fetch_datum_iterator to fetch datums from disk to input buffer.
> > 4. If the data in the input buffer is compressed, extract some data from
> the input buffer to the output buffer until the caller's
> >     needs are met.
> >
> > I've implemented the prototype and apply it to the position() function
> to test performance.
>
> Hi Binguo,
>
> Interesting work, and nice performance improvements so far.  Just by
> the way, the patch currently generates warnings:
>
> https://travis-ci.org/postgresql-cfbot/postgresql/builds/554345719
>
> --
> Thomas Munro
> https://enterprisedb.com
>