Re: Query Assistance

All...

I have a simple table in PostgreSQL 8.2.5:

CREATE TABLE power_transitions (
-- Transition ID (PK)
tid integer NOT NULL,
-- State ID (0 = Unknown, 1 = Online (AC power), 2 = Offline (Battery)
sid smallint NOT NULL,
-- Timestamp of transition
statetime timestamp without time zone DEFAULT now() NOT NULL,
-- Is this a real outage?
is_outage boolean DEFAULT true NOT NULL
);

It contains a log of power outages (transitions). I'd like to create
query that returns a transition offline time and associated return to
online time. Is there a better way of handling this? I am open to
schema change suggestions. Thanks very much!

-- Gary Chambers

// Nothing fancy and nothing Microsoft!

On Wed, 12 Dec 2007 11:58:20 -0500
"Gary Chambers" <gwchamb(at)gmail(dot)com> wrote:
> All...
>
> I have a simple table in PostgreSQL 8.2.5:
>
> CREATE TABLE power_transitions (
> -- Transition ID (PK)
> tid integer NOT NULL,
> -- State ID (0 = Unknown, 1 = Online (AC power), 2 = Offline (Battery)
> sid smallint NOT NULL,
> -- Timestamp of transition
> statetime timestamp without time zone DEFAULT now() NOT NULL,
> -- Is this a real outage?
> is_outage boolean DEFAULT true NOT NULL
> );
>
> It contains a log of power outages (transitions). I'd like to create
> query that returns a transition offline time and associated return to
> online time. Is there a better way of handling this? I am open to
> schema change suggestions. Thanks very much!

Have you considered this?

CREATE TABLE power_transitions (
-- Transition ID (PK)
tid integer NOT NULL,
-- Timestamp of power off (
starttime timestamp without time zone DEFAULT now() NOT NULL,
-- Timestamp of power on (
endtime timestamp without time zone,
-- Is this a real outage? may not be needed.
is_outage boolean DEFAULT true NOT NULL
);

The is_outage bool could be handled with special timestamps (e.g.
EPOCH) but I am not sure what it signifies to you. Of course you have
to deal with false transitions but I don't know what your information
capture system is so I can't work out all the details but this seems
like a good base for what you want. Every row that has a valid start
and end time is a complete record of an outage.

I am also thinking of a scheme that uses two tables but I don't really
know your environment or requirements. I am assuming that you spend
more time querying the table than updating it. If not your problem
isn't your database, it's your power plant. :-)

--
D'Arcy J.M. Cain <darcy(at)druid(dot)net> | Democracy is three wolves
http://www.druid.net/darcy/ | and a sheep voting on
+1 416 425 1212 (DoD#0082) (eNTP) | what's for dinner.

D'Arcy...

> Have you considered this?

I considered integrating the begin and end times into the table. I'm
capturing the data via ACPI events, so it's "transactional" by nature.
I want to be able to keep track of false transitions (hence the
is_outage field).

I'm looking for a way to simplify the transitions output on my web
browser, and I want to combine an offline and a corresponding online
time into a single line.

> I am also thinking of a scheme that uses two tables but I don't really
> know your environment or requirements. I am assuming that you spend
> more time querying the table than updating it. If not your problem
> isn't your database, it's your power plant. :-)

It's nothing complex at all. The power in my neighborhood is
infamously unstable, and I'm merely keep records to complain as much
as I can to the power company.

Thanks for taking the time to reply!

-- Gary Chambers

// Nothing fancy and nothing Microsoft!

Gary Chambers wrote:
> D'Arcy...
>
>> Have you considered this?
>
> I considered integrating the begin and end times into the table. I'm
> capturing the data via ACPI events, so it's "transactional" by nature.
> I want to be able to keep track of false transitions (hence the
> is_outage field).
>
> I'm looking for a way to simplify the transitions output on my web
> browser, and I want to combine an offline and a corresponding online
> time into a single line.

How about a "paired_with" field that references the power_transitions
table and a trigger. When you insert a new row, it checks what the
previous row was - if it's a down & this is an up, then set the
paired_with field on each.

--
Richard Huxton
Archonet Ltd