Re: Queues Problem

On 6/8/2010 11:53 AM, uaca man wrote:

Hello my fellow postgreSQL gurus. I´m a user of postgresSQL of quite
some time now, but most of my experience is consuming database, and for
the current project we are without a proper DBA and they have to bear
with me and so I must seek advice.

I have a list of building and a queue and the user can start the
construction of one or more building that will take some time to build.
The problems lies with the fact this is a web browser game and the user
can log in, star the construction and log off, to further aggravate the
problem another user may take a look at the buildings, to add a little
bit more, when a building is done it may have effect on the user
population, gold and whatever the “imagination team” can come up with.

Bottom line is: the construction has to be “concluded” with second’s
precision.

Lets say for a 20 thousand users server, it may have at most 20 thousand
constructions started at the same time.

To accomplish such behavior so far I could come up with two options:

1. Make a never ending function that will look at the BuildingQueue
table every second and finish the construction.

2. Every time the user start a construction add a cron job for that
construction to run 1 seconds after the construction is finished and
call a function the will finish.

For some reason I can not believe that a never ending function is a good
idea and I don’t think cron jobs are meant to have 20 thousand jobs.

Anyone care to share?

Tables:

Create table "Building"

(

"idBuilding" Serial NOT NULL,

"description" Varchar(200),

"time" Integer,

primary key ("idBuilding")

) Without Oids;

Create table "BuildingQueue"

(

"idBuilding" Integer NOT NULL,

"start" Timestamp,

"end" Timestamp,

primary key ("idBuilding")

) Without Oids;

Alter table "BuildingQueue" add foreign key ("idBuilding") references
"Building" ("idBuilding") on update restrict on delete restrict;

How about you figure out when "it should be finished", and if now() is after "should be" then mark the building as completed with a finish time of "should be".

Then you can run it whenever (every hour, on login, etc), and it'll catch up, and mark buildings as complete with the appropriate time.

-Andy