Re: Continuous inserts...

Hi All.

Shouldn't Postgres block while vacuuming, and then
continue inserting starting where it left off? Is the
time lag too much?

I am curious because I am going to build a similar app
soon, basically parsing and inserting log file
entries.

W
--- Stephan Szabo <sszabo(at)megazone23(dot)bigpanda(dot)com>
wrote:
>
> On Thu, 17 Aug 2000, Joerg Hessdoerfer wrote:
>
> > Hi!
> >
> > I have an application, where I have to insert data
> into a table at several
> > rows per second, 24 hours a day, 365 days a year.
> >
> > After some period (a week, maybe a month) the data
> will be reducted to some
> > degree and deleted from the table.
> >
> > As far as I understood, I would have to use VACUUM
> to really free the table
> > from deleted rows - but VACUUM (esp. on a table
> with several million rows)
> > takes some time and prevents me from inserting new
> data.
> >
> > Now, I thought I could just rename the table,
> inserting into a temp table, and
> > switch the tables back after VACUUMing. Ideally,
> this should work unnoticed
> > (and thus without prog. effort) on the client
> (inserter) side.
> >
> > Question: would it work to use a transaction to
> perform the rename?
> >
> > i.e.: continuous insert into table 'main' from
> client.
> >
> > From somewhere else, execute:
> >
> > begin;
> > alter table main rename to vac_main;
> > create table main (...);
> > end;
> >
> > would the inserter notice this? Read: would ALL
> inserts AT ANY TIME succeed?
>
> Unfortunately -- no. Also, bad things can happen if
> the transaction
> errors since the rename happens immediately.
> There's been talk on
> -hackers about this subject in the past.
>
> However, you might be able to do something like
> this, but
> I'm not sure it'll work and it's rather wierd:
>
> Have three tables you work with, a and b and c
>
> Set up rule on a to change insert to insert on b.
> Insert into a.
> When you want to vacuum, change the rule to insert
> to c.
> Vacuum b
> Change rule back
> move rows from a and c into b
> vacuum c
>
> [you will slowly lose space in a, but it should only
> be an occasional row since you should only insert
> into
> a while you've deleted the insert rule to b, but
> haven't yet added the insert rule to c -- not too
> many
> rows here]
>
>

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