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Thread: BDR Global Sequences

BDR Global Sequences

From
pbj@cmicdo.com
Date:
I have a question about BDR Global Sequences.

I've been playing with BDR on PG 9.4beta2, built from source from the
2nd Quadrant GIT page (git://git.postgresql.org/git/2ndquadrant_bdr.git).

When trying a 1000000 row \copy-in, letting PG choose the global sequence
values, I get "ERROR:  could not find free sequence value for global
sequence public.myseq", as documented...no surprise there.  However, the
number of rows I can load before the error varies wildly with each trial.

Is there way to increase a global sequence's reservation block for each
node so that I can tell the nodes, "I'm going to load 100M rows now so
you should get ready for that."?

PJ

Re: BDR Global Sequences

From
Andres Freund
Date:
Hi,

On 2014-09-29 13:52:52 -0700, pbj@cmicdo.com wrote:
> I have a question about BDR Global Sequences.
>
> I've been playing with BDR on PG 9.4beta2, built from source from the
> 2nd Quadrant GIT page (git://git.postgresql.org/git/2ndquadrant_bdr.git).
>
> When trying a 1000000 row \copy-in, letting PG choose the global sequence
> values, I get "ERROR:  could not find free sequence value for global
> sequence public.myseq", as documented...no surprise there.  However, the
> number of rows I can load before the error varies wildly with each trial.

Yea, it depends on how quick the refilling starts and how quickly it can
keep up. The next version hopefull will start to fill up a bit quicker.

> Is there way to increase a global sequence's reservation block for each
> node so that I can tell the nodes, "I'm going to load 100M rows now so
> you should get ready for that."?

Not yet, but we're planning to add that.

Greetings,

Andres Freund

--
 Andres Freund                       http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

Re: BDR Global Sequences

From
pbj@cmicdo.com
Date:
Hi Andres,

 > Hi,
 >
 > On 2014-09-29 13:52:52 -0700, pbj@cmicdo.com wrote:
 >> I have a question about BDR Global Sequences.
 >>
[deleted]
 >> Is there way to increase a global sequence's reservation block for each
 >> node so that I can tell the nodes, "I'm going to load 100M rows now so
 >> you should get ready for that."?
 >
 >
 > Not yet, but we're planning to add that.

Good to hear.  In the meantime, is there something I can hack to force
the nodes to make a sequence allocation of my choosing (even if just
hardwired?)  I was playing with start_elections_sql where it says:

        generate_series(\n"
                current_max,\n"
                -- 1000 is the chunk size, -1 is to get < instead <= out of generate_series\n"
                current_max + 1000 * (5 - open_seq_chunks) - 1,\n"
                1000) chunk_start\n"

and hoping that bumping up the 1000 would help, but apparently not.

PJ

 >
 > Greetings,
 >
 > Andres Freund
 >
 > --
 > Andres Freund                       http://www.2ndQuadrant.com/
 > PostgreSQL Development, 24x7 Support, Training & Services
 >