Обсуждение: Transaction costs?

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Transaction costs?

От
Philip Warner
Дата:
Just wondering what the cost of begin/end transaction is.

This is for pg_dump which, when restoring BLOBs, inserts multiple rows into
a temporary xref table. The sequence of events is:

Conn1: Begin
Conn1: lo_create/lo_close/lo_write.../lo_close
Conn2: Insert into xref table (which does an implicit begin/end, I think).
Conn1: Commit;

Would I get substantially better performance by doing a begin/end every
10/100/1000 rows in each connection, or is the transaction overhead low? Or
is this something I just need to test?

[eg. in Dec/RDB TX begin/end is expensive, but writing more than 1000 rows
in a TX can also be costly, so a compromise is useful]

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Re: Transaction costs?

От
Tom Lane
Дата:
Philip Warner <pjw@rhyme.com.au> writes:
> This is for pg_dump which, when restoring BLOBs, inserts multiple rows into
> a temporary xref table. The sequence of events is:

> Conn1: Begin
> Conn1: lo_create/lo_close/lo_write.../lo_close
> Conn2: Insert into xref table (which does an implicit begin/end, I think).
> Conn1: Commit;

Two connections?  Why in the world are you doing it like that --- and
especially in that order?  Seems like this is committing an xref change
before the LO itself is committed.  Why?
        regards, tom lane

Re: Transaction costs?

От
Philip Warner
Дата:
At 11:33 2/11/00 -0500, Tom Lane wrote:
>> Conn1: Begin
>> Conn1: lo_create/lo_close/lo_write.../lo_close
>> Conn2: Insert into xref table (which does an implicit begin/end, I think).
>> Conn1: Commit;
>
>Two connections?

Otherwise a reconnect will lose the temp table contents.


----------------------------------------------------------------
Philip Warner                    |     __---_____
Albatross Consulting Pty. Ltd.   |----/       -  \
(A.B.N. 75 008 659 498)          |          /(@)   ______---_
Tel: (+61) 0500 83 82 81         |                 _________  \
Fax: (+61) 0500 83 82 82         |                 ___________ |
Http://www.rhyme.com.au          |                /           \|                                |    --________--
PGP key available upon request,  |  /
and from pgp5.ai.mit.edu:11371   |/