Re: Disk buffering of resultsets

I don't think i've heard any talk of using features that are 9.4
server/protocol specific. You'll of course need the updated jdbc driver
and (I'm taking an educated guess here) that this is too much to check in
for the 9.4 JDBC driver release. Perhaps it could be an experimental
feature that could be optionally compiled in during early days of the
iterative design, develop/test, tweak cycle before stability is reached.

On Tue, Oct 14, 2014 at 4:09 AM, Enrico Olivelli - Diennea <
enrico(dot)olivelli(at)diennea(dot)com> wrote:

> Hi,
>
> we can give support doing some benchs with our platform as soon as some
> ALFA/BETA will be available.
>
> We are longing for this series of improvements!
>
> I hope that these features could be used with 9.3 server and that we won’t
> need to upgrade to 9.4 (which is not still stable )
>
>
>
> Thank you very much
>
>
>
> *Enrico Olivelli*
> Software Development Manager @Diennea
> Tel.: (+39) 0546 066100 - Int. 925
> Viale G.Marconi 30/14 - 48018 Faenza (RA)
>
> MagNews - E-mail Marketing Solutions
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> http://www.diennea.com
>
>
>
>
>
> *Da:* pgsql-jdbc-owner(at)postgresql(dot)org [mailto:
> pgsql-jdbc-owner(at)postgresql(dot)org] *Per conto di *Vitalii Tymchyshyn
> *Inviato:* lunedì 13 ottobre 2014 17:34
> *A:* Craig Ringer
> *Cc:* Tom Lane; John R Pierce; PG-JDBC Mailing List
> *Oggetto:* Re: [JDBC] Disk buffering of resultsets
>
>
>
> Hello, again.
>
>
>
> Sorry for the pause, I had a really busy week. Yet it allowed me to think
> a little more.
>
> As for me, there are three independent goals that can be addressed
> independently:
>
>
>
> 1) Prevent OOMs
>
> Unfortunately this can be addressed with out of heap saving only. The way
> I did in draft would still OOM when secondary query comes.
>
> Note that it's not that unusual. It's usually used without any
> multithreading to perform a client-side join, e.g. when complicated
> inheritance scenario is in place or to load some dictionary data without
> much duplication (e.g. only few wide dictionary entries for the long
> query), ...
>
> I am still thinking to do it without much parsing (you will need record
> type and size and that's all, without field parsing) by simply copying
> as-is to temp file. Pluggable interfaces can be done later if needed.
>
>
>
> 2) Fast first record
>
> Here we need to introduce strategies for "who is doing copying and when"
> from (1). I propose pluggable strategies with few predefined (see below).
> User can pass predefined strategy name or an Executor as a DataSource
> parameter or static method reference that returns an Executor when a string
> is needed (e.g. in connection URI). This would also allow to easily point
> to Executors.* methods. We may think about ScheduledExecutor requirement to
> also reuse it for QueryTimeout stuff.
>
>
>
> I propose to have next predefined strategies:
>
> a) Direct executor, that does all loading at the very beginning,
> potentially saving to a temp file.
>
> b) Postponed executor, that works much like in my draft: reads as needed
> without any disk saving. Performs disk saving only when connection is
> needed for some other statement.
>
> c) JVM-wide Executors.newCachedThreadPool that will start offloading in
> parallel as fetchSize is reached.
>
>
>
> Also I'd propose to set default fetchSize to some reasonable value, like
> 1000 and specify one of the strategies (e.g (a)) as default so that we
> won't get OOM on default settings. Or we should allow to set default fetch
> size on connection/data source level (or both).
>
>
>
> 3) Fast cancel/resultset close.
>
> It's the only place where switching to portals is needed as far as I can
> see and it can be done orthogonal to (1) and (2). I don't see any other
> goal that will benefit from it. To be honest, I am willing to do (1) and
> (2), but not (3) because this would mean me to get much deeper into the
> protocol I know almost nothing about right now.
>
>
>
> Best regards, Vitalii Tymchyshyn.
>
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