Re: Optimize query for listing un-read messages

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От Andreas Joseph Krogh
Тема Re: Optimize query for listing un-read messages
Дата
Msg-id OfficeNetEmail.75.5efec2c7653ca1ac.145bbcd4e27@prod2
обсуждение исходный текст
Ответ на Re: Optimize query for listing un-read messages  (Craig James <cjames@emolecules.com>)
Ответы Re: Optimize query for listing un-read messages  (Vitalii Tymchyshyn <vit@tym.im>)
Список pgsql-performance
På fredag 02. mai 2014 kl. 02:17:58, skrev Craig James <cjames@emolecules.com>:
On Thu, May 1, 2014 at 4:26 AM, Andreas Joseph Krogh <andreas@visena.com> wrote:
I have a schema where I have lots of messages and some users who might have read some of them. When a message is read by a user I create an entry i a table message_property holding the property (is_read) for that user.
 
The schema is as follows:
[...]
 
create table person(
    id serial primary key,
    username varchar not null unique
);
 
create table message(
    id serial primary key,
    subject varchar
);
 
create table message_property(
    message_id integer not null references message(id),
    person_id integer not null references person(id),
    is_read boolean not null default false,
    unique(message_id, person_id)
);
 
[...]
 So, for person 1 there are 10 unread messages, out of a total 1mill. 5 of those unread does not have an entry in message_property and 5 have an entry and is_read set to FALSE.
 
Here's a possible enhancement: add two columns, an indexed timestamp to the message table, and a "timestamp of the oldest message this user has NOT read" on the person table. If most users read messages in a timely fashion, this would (in most cases) narrow down the portion of the messages table to a tiny fraction of the total -- just those messages newer than the oldest message this user has not read.
 
When you sign up a new user, you can set his timestamp to the time the account was created, since presumably messages before that time don't apply.
 
Whether this will help depends a lot on actual use patterns, i.e. do users typically read all messages or do they leave a bunch of unread messages sitting around forever?
 
Thanks fort the suggestion. A user must be able to read arbitrary old messages, and messages don't expire.
 
--
Andreas Jospeh Krogh
CTO / Partner - Visena AS
Mobile: +47 909 56 963
 
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