Restricting the value of columns in PostgreSQL

ENUM

--Enum type
 --case sensitive
 --4 Bytes on disk
 CREATE TYPE vaildcolor AS ENUM ('Blue','Pink');

REGEXP
--Case insensitivie regexp
 --accepts NULL
 --useful for complex/long text matching
 ALTER TABLE color ADD CONSTRAINT
 vaild_color CHECK(
 color ~*
 '^(blue|pink)$'
 );

CHECHK
 --Case sensitivie =
 --accepts NULL
 ALTER TABLE color ADD CONSTRAINT
 vaild_color CHECK(
 color = 'Blue' OR color = 'Pink'
 );

			

post sobre sustentabilidad de transporte en grandes ciudades

Interesante post sobre sustentabilidad de transporte en grandes ciudades

http://mexicoparalosmexicanos.blogspot.com/2011/08/autopistas-urbanas-su-historia-y.html

master/worker pattern

• A master UE sets up a pool of workers process/threads and a bag of tasks. (Workers are like UE)

• Workers process concurrently tasks from the bag

Each worker continues processing, until all tasks have been processed or some other condition has been reached. In some implementations no explicit master is present.

- It is suitable for non-deterministic execution time of tasks.

- It is used when tasks should be distributed among workers.

- Since creating and terminating processes/threads is expensive workers should be reused.

- Not applicable when tasks are interdependent.

- Usually the number of tasks exceeds the number of UEs.

- Usually number of workers <= PE.

How tasks are assigned to workers?