expand a varchar column very slowly , why?
- by francs
Hi
We need to modify a column of a big product table , usually normall ddl statments will be
excutely fast ,but the above ddl statmens takes about 10 minnutes?I wonder know the reason!
I just want to expand a varchar column?The following is the detailsl
--table size
wapreader_log= select pg_size_pretty(pg_relation_size('log_foot_mark'));
pg_size_pretty
----------------
5441 MB
(1 row)
--table ddl
wapreader_log= \d log_foot_mark
Table "wapreader_log.log_foot_mark"
Column | Type | Modifiers
-------------+-----------------------------+-----------
id | integer | not null
create_time | timestamp without time zone |
sky_id | integer |
url | character varying(1000) |
refer_url | character varying(1000) |
source | character varying(64) |
users | character varying(64) |
userm | character varying(64) |
usert | character varying(64) |
ip | character varying(32) |
module | character varying(64) |
resource_id | character varying(100) |
user_agent | character varying(128) |
Indexes:
"pk_log_footmark" PRIMARY KEY, btree (id)
--alter column
wapreader_log= \timing
Timing is on.
wapreader_log= ALTER TABLE wapreader_log.log_foot_mark ALTER column user_agent TYPE character varying(256);
ALTER TABLE
Time: 603504.835 ms
