Hi all,

I have a table with a little over 200,000 columns in it that I need to update using a regular expression. I admit that though I am not a beginner and postgres, I am also far from an expert. :p

I tried to create an Index that would optimize the UPDATE but I may have made an error in how I built it. Here is the table structure, the index I tried to create and an 'EXPLAIN ANALYZE' of the UPDATE (though I am still just now learning how to use 'EXPLAIN').

tle-bu=> \d file_info_3
Table "public.file_info_3"
Column | Type | Modifiers
file_group_name | text | not null
file_group_uid | bigint | not null
file_mod_time | bigint | not null
file_name | text | not null
file_parent_dir | text | not null
file_perm | text | not null
file_size | bigint | not null
file_type | character varying(2) | not null default 'f'::character varying
file_user_name | text | not null
file_user_uid | bigint | not null
file_backup | boolean | not null default true
file_display | boolean | not null default false
file_restore | boolean | not null default false
"file_info_3_display_idx" btree (file_type, file_parent_dir, file_name)

  Here is the EXPLAIN:

tle-bu=> EXPLAIN ANALYZE UPDATE file_info_3 SET file_backup='f' WHERE file_parent_dir~'^/home' OR (file_parent_dir='/' AND file_name='home');
Seq Scan on file_info_3 (cost=0.00..7770.00 rows=1006 width=206) (actual time=1050.813..5648.462 rows=67835 loops=1)
Filter: ((file_parent_dir ~ '^/home'::text) OR ((file_parent_dir = '/'::text) AND (file_name = 'home'::text)))
Total runtime: 68498.898 ms
(3 rows)

I thought that it would have used the index because 'file_parent_dir' and 'file_name' are in the index but is I am reading the "EXPLAIN" output right it isn't but is instead doing a sequencial scan. If that is the case, how would I best built the index? Should I have just used the 'file_parent_dir' and 'file_name'?

  Thanks all!!


Madison Kelly (Digimer)
TLE-BU, The Linux Experience; Back Up

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TIP 8: explain analyze is your friend

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