Joost van der Sluis wrote:
Since this is strictly read-only, I can't see why I need transactions,
but I obviously respect the judgment of whoever designed the architecture.
Well, you always need a transaction. Without a transaction, Postgres
will do nothing, ever.
I assume you are used to the fact that postgres automatically creates an
transaction for you. With Sqldb you have to do this yourself.
Please excuse me for threading onto a fairly old message. In the
specific case of PostgreSQL, if I use SELECT * FROM pg_stat_activity to
examine backend state I can see that a Lazarus TSQLQuery, i.e. that has
to have an associated transaction object, is explicitly marked as being
in a transaction, while other methods of access (Delphi+BDE, PGAdmin3)
are not.
The reason I mention this is that I find myself wondering whether a
program written with Lazarus/FPC, particularly one that used db-aware
components, could keep a table in a state where housekeeping activities
(in particular vacuum) couldn't access it- I'm currently troubleshooting
a similar problem created by other software.
The first row in the table below is associated with the connection
object, the second is associated with a query which is being kept
connected for a few minutes (I'm assuming that when it is inactivated
the contents are inaccessible). The third isn't from Lazarus but from
PGAdmin3. The table is select-only to both users.
datid | datname | procpid | usesysid | usename | current_query |
-------+----------+---------+----------+---------+---------------------+-
32213 | open2300 | 23937 | 16397 | markMLl | <IDLE> |
32213 | open2300 | 4570 | 16397 | markMLl | <IDLE> in transactio|
32213 | open2300 | 28688 | 16395 | jamesFP | <IDLE> |
waiting | xact_start | query_start
---------+-------------------------------+-------------------------------
f | | 2010-12-08 09:14:21.051523+00
f | 2010-12-10 08:48:33.972094+00 | 2010-12-10 08:48:34.002003+00
f | | 2010-12-10 00:38:02.822295+00
| backend_start | client_addr | client_port
+-------------------------------+--------------+------------
| 2010-12-08 09:14:20.41357+00 | 192.168.1.16 | 39868
| 2010-12-10 08:48:33.961539+00 | 192.168.1.16 | 51489
| 2010-10-05 12:32:48.512251+00 | 192.168.1.64 | 43538
(3 rows)
--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk
[Opinions above are the author's, not those of his employers or colleagues]
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