IDS Forum

Re: HDR secondary : new rows not seen on secondary

Posted By: Fernando Nunes
Date: Thursday, 20 February 2014, at 7:06 a.m.

In Response To: Re: HDR secondary : new rows not seen on secondary (Art Kagel)

The link:

http://informix-technology.blogspot.sk/2014/02/new-feature-nova-funcionalidade.html

But I wouldn't call it a comparison in terms of performance and more
important it didn't include HDR and that's a key factor here.
On the several attempts I've made, naturally buffered logging was
consistently faster. But I had only one session, I was running on a VM
(where the I/O is naturally bad) etc.
I'm not sure if the version was stated, but I'd pay more attention to
Madison's suggestion about the new parameters.

In an HDR environment, the flush of the logical log buffer copies data to
the "replication buffers" which are 12 (not configurable). If there is no
space free in these buffers, the primary will slow down (flag G). If you
see a lot of G flags you're having this problem. Otherwise you're safe.
The complete flux of these buffers are not clearly docuemnted, although
there was a chat with the labs about HDR/MACH 11 performance that covered
it somehow and I think I've seen some detailed references to how this
works... not sure if it was here (probably on a Madison's post) or
eventually in internal stuff like PMRs...

Good network is important. Also keep in mind (and this is the main point in
my article), that BUFFERED logging has durability implications... And most
customers prefer full security over some undetermined performance gain
(that's why I suggested a new feature and registered it on RFE site).

Also note that in BUFFERED mode, Informix may never write the logical log
buffer if there is no more activity on the database... Other RDBMs will do
it after some time (DB2 seems to write it at most each second, and there
are references that mention Oracle would do it at most each 3 seconds,
although official documentation is terribly vague - something like "it will
flush after a sufficient activity happens" - )
I didn't make this clear on the post because I only verified it later, but
if you have a large enough buffer and you're "alone" on the database, if
you're using BUFFERED mode, things will stay in the buffer (I think a
checkpoint will flush it). Naturally this is not a very usual situation,
specially if you have the DB scheduler active.

On Thu, Feb 20, 2014 at 11:48 AM, Art Kagel <art.kagel@gmail.com> wrote:

> Fernando did some testing of the performance of BUFFERED versus UNBUFFERED
> logging in his latest blog entry. Check it out.
>
> Art
>
> Art S. Kagel, Principal Consultant
> ASK Database Management
>
> Blog: http://informix-myview.blogspot.com/
>
> Disclaimer: Please keep in mind that my own opinions are my own opinions
> and do not reflect on the IIUG, nor any other organization with which I am
> associated either explicitly, implicitly, or by inference. Neither do
> those opinions reflect those of other individuals affiliated with any
> entity with which I am affiliated nor those of the entities themselves.
>
> On Thu, Feb 20, 2014 at 5:39 AM, FABRICE PLATEL <fplatel@orinux.com>
> wrote:
>
> > Thanks a lot Madison and Art for your answers.
> > effectively it solved the problem, I am just wondering what will be the
> > drawback in term of performance when a lot of concurrent transactions
> will
> > perform their commits.
> >
> >
> >
> >
>
> *******************************************************************************
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> >
> >
>
> --089e0122797adca63a04f2d51552
>
>
>
> *******************************************************************************
> Forum Note: Use "Reply" to post a response in the discussion forum.
>
>

--
Fernando Nunes
Portugal

http://informix-technology.blogspot.com
My email works... but I don't check it frequently...

--001a1133938601c4ce04f2d554de

Messages In This Thread

• HDR secondary : new rows not seen on secondary
  FABRICE PLATEL -- Wednesday, 19 February 2014, at 6:06 p.m.
  • Re: HDR secondary : new rows not seen on secondary
    Madison Pruet -- Wednesday, 19 February 2014, at 6:12 p.m.
    • Re: HDR secondary : new rows not seen on secondary
      FABRICE PLATEL -- Thursday, 20 February 2014, at 5:39 a.m.
      • Re: HDR secondary : new rows not seen on secondary
        Fernando Nunes -- Thursday, 20 February 2014, at 5:54 a.m.
      • Re: HDR secondary : new rows not seen on secondary
        Art Kagel -- Thursday, 20 February 2014, at 6:48 a.m.
        • Re: HDR secondary : new rows not seen on secondary
          Fernando Nunes -- Thursday, 20 February 2014, at 7:06 a.m.
  • Re: HDR secondary : new rows not seen on secondary
    Art Kagel -- Wednesday, 19 February 2014, at 6:18 p.m.

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