Re: [GENERAL] time series data - Mailing list pgsql-general
On Sun, Oct 1, 2017 at 6:20 PM, Clifford Snow <clifford@snowandsnow.us> wrote:
I have a stream that updates every minute with a trigger that updates another table with information from the stream. That way I'm constantly updated with no need to run a script to update before I want a report.Clifford--On Sun, Oct 1, 2017 at 10:08 AM, Melvin Davidson <melvin6925@gmail.com> wrote:On Sun, Oct 1, 2017 at 4:17 AM, Khalil Khamlichi <khamlichi.khalil@gmail.com> wrote:Hi everyone,I have a data stream of a call center application coming in to postgres in this format :user_name, user_status, event_time'user1', 'ready', '2017-01-01 10:00:00''user1', 'talking', '2017-01-01 10:02:00''user1', 'after_call', '2017-01-01 10:07:00''user1', 'ready', '2017-01-01 10:08:00''user1', 'talking', '2017-01-01 10:10:00''user1', 'after_call', '2017-01-01 10:15:00''user1', 'paused', '2017-01-01 10:20:00'......so as you see each new insert of an "event" is in fact the start_time of that event and also the end_time of the previous one so should be used to calculate the duration of this previous one.What is the best way to get user_status statistics like total duration, frequency, avg ...etc , does any body have an experience with this sort of data streams ?Thanks in advance.
Just a suggestion, but here is what I would do.
First, create your tables similar to as follows
CREATE TABLE status
(
call_status varchar(10) NOT NULL,
CONSTRAINT status_pk PRIMARY KEY (call_status)
);
INSERT INTO status
(call_status)
VALUES
('ready'),
('talking'),
('after_call');
CREATE TABLE user_sessions
(
username name NOT NULL,
session_id bigint NOT NULL,
call_status varchar(10) NOT NULL,
call_time timestamp NOT NULL,
CONSTRAINT user_sessions_pk PRIMARY KEY (username, session_id,call_status),
CONSTRAINT user_sessions_fk_status FOREIGN KEY (call_status)
REFERENCES status(call_status)
);
Next, you will need to generate a unique session_id for each
user, but only for when call_status is 'ready'. So probably
a table of the form:
CREATE TABLE current_session
(
username name NOT NULL,
session_id serial NOT NULL,
CONSTRAINT current_session_pk PRIMARY KEY (username)
);
Then all you need to do is:
1. Update current_session and get the new session_id each time a user connects (call_status = 'ready'.
Probably best to use a BEFORE trigger to do this, but you will need to code it yourself.2. You can then do
SELECT username,
age ( (SELECT call_time FROM current_session WHERE call_status = 'talking'),
( SELECT call_time FROM current_session WHERE call_status = 'after_call')
) as duration
FROM user_sessions
WHERE username = 'actual_user_name'
AND session_id = actual_session_id;You can use similar queries for avg and frequency.
--Melvin Davidson
I reserve the right to fantasize. Whether or not you
wish to share my fantasy is entirely up to you.
I thought about the table design for user_sessions and came up
with a better one:
CREATE TABLE user_sessions
(
username name NOT NULL,
session_id bigint NOT NULL,
call_status varchar(10) NOT NULL,
call_ready timestamp NOT NULL,
call_talking timestamp,
call_after_call timestamp,
call_duration interval,
CONSTRAINT user_sessions_pk PRIMARY KEY (username, session_id),
CONSTRAINT user_sessions_fk_status FOREIGN KEY (call_status)
REFERENCES status(call_status)
);
So in essence, when the call starts, just do:
INSERT INTO user_sessions
(username, call_ready)
VALUES
('actual_user_name', now() );
Then
SELECT max(session_id) AS current_session
FROM user_sessions
WHERE username = 'actual_user_name';
When talking starts:
UPDATE user_sessions
SET call_status = 'talking',
call_talking = now()
WHERE username = 'actual_user_name'
AND session_id = current_session;
When call ends:
UPDATE user_sessions
SET call_status = 'after_call',
call_after_call = now()
WHERE username = 'actual_user_name'
AND session_id = current_session;
Now all you have to do to get call length is:
SELECT username,
age ( call_after_call, call_talking ) as duration
FROM user_sessions
WHERE username = 'actual_user_name'
AND session_id = current_session;
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