Horton

Re: Parallel copy

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: David Fetter <david@fetter.org>
Cc: Ants Aasma <ants@cybertec.at>, Alastair Turner <minion@decodable.me>, Thomas Munro <thomas.munro@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Date: 2020-02-19T04:08:15Z
Lists: pgsql-hackers

Commits

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  1. Allow WaitLatch() to be used without a latch.

  2. Add %P to log_line_prefix for parallel group leader

  3. Include replication origins in SQL functions for commit timestamp

  4. Avoid useless buffer allocations during binary COPY FROM.

On Tue, Feb 18, 2020 at 8:41 PM David Fetter <david@fetter.org> wrote:
>
> On Tue, Feb 18, 2020 at 06:51:29PM +0530, Amit Kapila wrote:
> > On Tue, Feb 18, 2020 at 5:59 PM Ants Aasma <ants@cybertec.at> wrote:
> > >
> > > On Tue, 18 Feb 2020 at 12:20, Amit Kapila <amit.kapila16@gmail.com> wrote:
> > > > This is something similar to what I had also in mind for this idea.  I
> > > > had thought of handing over complete chunk (64K or whatever we
> > > > decide).  The one thing that slightly bothers me is that we will add
> > > > some additional overhead of copying to and from shared memory which
> > > > was earlier from local process memory.  And, the tokenization (finding
> > > > line boundaries) would be serial.  I think that tokenization should be
> > > > a small part of the overall work we do during the copy operation, but
> > > > will do some measurements to ascertain the same.
> > >
> > > I don't think any extra copying is needed.
> >
> > I am talking about access to shared memory instead of the process
> > local memory.  I understand that an extra copy won't be required.
>
> Isn't accessing shared memory from different pieces of execution what
> threads were designed to do?
>

Sorry, but I don't understand what you mean by the above?  We are
going to use background workers (which are processes) for parallel
workers.  In general, it might not make a big difference in accessing
shared memory as compared to local memory especially because the cost
of other stuff in the copy is relatively higher.  But still, it is a
point to consider.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com