On Thu, Jan 12, 2017 at 2:19 PM, btober@computer.org
<btober@broadstripe.net> wrote:
>
>
> ----- Original Message -----
>> From: "Jonathan Vanasco" <postgres@2xlp.com>
>> To: "pgsql-general general" <pgsql-general@postgresql.org>
>> Sent: Thursday, January 12, 2017 3:06:14 PM
>> Subject: [GENERAL] efficiently migrating 'old' data from one table to another
>>
>> I'm just wondering if there's a more efficient way of handling a certain
>> periodic data migration.
>>
>> We have a pair of tables with this structure:
>>
>> table_a__live
>> column_1 INT
>> column_2 INT
>> record_timestamp TIMESTAMP
>>
>> table_a__archive
>> column_1 INT
>> column_2 INT
>> record_timestamp TIMESTAMP
>>
>> periodically, we must migrate items that are 'stale' from `table_a__live ` to
>> `table_a__archive`. The entries are copied over to the archive, then
>> deleted.
>>
>> The staleness is calculated based on age-- so we need to use INTERVAL. the
>> "live" table can have anywhere from 100k to 20MM records.
>>
>> the primary key on `table_a__live` is a composite of column_1 & column_2,
>>
>> In order to minimize scanning the table, we opted to hint migrations with a
>> dedicated column:
>>
>> ALTER TABLE table_a__live ADD is_migrate BOOLEAN DEFAULT NULL;
>> CREATE INDEX idx_table_a__live_migrate ON table_a__live(is_migrate) WHERE
>> is_migrate IS NOT NULL;
>>
>> so our migration is then based on that `is_migrate` column:
>>
>> BEGIN;
>> UPDATE table_a__live SET is_migrate = TRUE WHERE record_timestamp <
>> transaction_timestamp() AT TIME ZONE 'UTC' - INTERVAL '1 month';
>> INSERT INTO table_a__archive (column_1, column_2, record_timestamp) SELECT
>> column_1, column_2, record_timestamp FROM table_a__live WHERE is_migrate IS
>> TRUE;
>> DELETE FROM table_a__live WHERE is_migrate IS TRUE;
>> COMMIT;
>>
>> The inserts & deletes are blazing fast, but the UPDATE is a bit slow from
>> postgres re-writing all the rows.
>>
>> can anyone suggest a better approach?
>>
>> I considered copying everything to a tmp table then inserting/deleting based
>> on that table -- but there's a lot of disk-io on that approach too.
>
>
> Review manual section 7.8.2. Data-Modifying Statements in WITH
>
>
> https://www.postgresql.org/docs/9.6/static/queries-with.html
this.
with data as (delete from foo where ... returning * ) insert into
foo_backup select * from data;