declere\(em declare a cursor

.nf

\fBdeclare\fR [\fBbinary\fR ]\fBcursorfor\fR select statement

.fi

.BR Declare

allows a user to create cursors.

Cursors are only available in transactions.

.PP

Normal cursors return data back in ASCII format. Since data is stored

natively in binary format, the system must do a conversion to produce

the ASCII format. In addition, ASCII formats are often larger in size

than binary format. Once the attributes come back in ASCII, often the

client application then has to convert it to a binary format to

manipulate it anyway.

.PP

\fBBinary\fR cursors give you back the data in the native binary

representation. Thus, binary cursors will tend to be a little faster

since there's less overhead of conversion.

.PP

However, ASCII is architectural neutral whereas binary representation

can differ between different machine architecture. Thus, if your client

machine uses a different representation than you server machine, getting

back attributes in binary format is probably not what you want. Also, if

your main purpose is displaying the data in ASCII, then getting it back

in ASCII will save you some effort on the client side.

.PP

For an example, see the fetch(l) manual page.

fetch(l),

begin(l),

end(l),

select(l).

fetch\(em fetch instance(s) from a cursor

close(l),

move(l),

select(l).

Currently, the smallest transaction in Postgres is a single SQL

command. It should be possible for a single fetch to be a

transaction.

vacuum\(em vacuum a database

.PP

The purge(l) command can be used to control the archive retention

characteristics of a given table.

.PP

If the server crashes during a vacuum command, chances are it will leave

a lock file hanging around. Attempts to re-run the vacuum command

result in an error message about the creation of a lock file. If you

are sure vacuum is not running, remove the pg_vlock file in your

database directory(i.e. data/base/dbname/pg_vlock).

purge(l).