Re: duda sobre truncate

Hola Gustavo

el truncate trunca la tabla, lo que creo que hace fisicamente es que marca
el primer registro
como fin de archivo, de manera tal que cuando lee la tabla lee 0 registros.
Lo mismo debe hacer con los indices, de manera tal que es una operacion
muy rapida.
de: http://www.postgresql.org/docs/9.1/static/sql-truncate.html
fijate lo que dice aca:
Notes

You must have the TRUNCATE privilege on a table to truncate it.

TRUNCATE acquires an ACCESS EXCLUSIVE lock on each table it operates on,
which blocks all other concurrent operations on the table. When RESTART
IDENTITY is specified, any sequences that are to be restarted are likewise
locked exclusively. If concurrent access to a table is required, then the
DELETE command should be used instead.

TRUNCATE cannot be used on a table that has foreign-key references from
other tables, unless all such tables are also truncated in the same
command. Checking validity in such cases would require table scans, and the
whole point is not to do one. The CASCADE option can be used to
automatically include all dependent tables — but be very careful when using
this option, or else you might lose data you did not intend to!

TRUNCATE will not fire any ON DELETE triggers that might exist for the
tables. But it will fire ON TRUNCATE triggers. If ON TRUNCATE triggers are
defined for any of the tables, then all BEFORE TRUNCATE triggers are fired
before any truncation happens, and all AFTER TRUNCATE triggers are fired
after the last truncation is performed and any sequences are reset. The
triggers will fire in the order that the tables are to be processed (first
those listed in the command, and then any that were added due to cascading).

salu2
jmdc

2013/7/1 Gustavo Hernández Delgado <gustavo(dot)hernandez(at)etecsa(dot)cu>

>
> Saludos a todos:
>
> Tengo una curiosidad: qué pasa cuando se hace un truncate a una tabla que
> está siendo consultada por muchas personas, o sea me gustaría saber qué
> hace postgres, por ejemplo va borrando artículos no consultados y así
> sucesivamente hasta que borra todo, etc
>
> gracias
>
>
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