Updating Royal Mail PAF data and ignorance about PostgreSQL deferred foreign keys

A few months ago I bashed together a pl/pgsql function for importing Royal Mail PAF
data into PostgreSQL
and at the same time I also put together another function to perform an update from their “changes” files.

Today I came to actually try and use that function, and it’s not much of a surprise that it needed a little more work; at the time I was working off a fresh import and a small set of changes, whilst looking (with squinty eyes) at the fairly long winded docs. The changes files from RM are supplied as a journal of changes, which I can only assume were intended to be read and applied sequentially; this means we have to rely on some of the smarts SQL provides us with to apply them in bulk. The docs even try to dissuade the use of the changes files by saying “Applying Changes files regularly is ‘high maintenance’, because applying thousands of changes is a very long & involved process compared to buying full refreshes”, however I don’t want to do full refreshes as that’s likely to cause more interruption, and besides it just seems a bit of a cop out to me.

So after another quick skim over the docs, I made a couple of corrections to the update function where I’d complicated things by replacing blank key columns with nulls, and added in an update procedure for the Alias and Postzon files (which are only supplied as a full refresh), this time using postgis to generate the latitude and longitude and save running my horrible perl script.

Then I had a go at running the update:

TEST=# BEGIN;
TEST=# SELECT update_pc_paf('Y14M04', '/tmp');
NOTICE:  2014-05-22 19:40:00.161582+01: Import starting for edition Y14M04 with data root /tmp/Y14M04_CHANGES/
NOTICE:  2014-05-22 19:40:00.165233+01: Begin staging Changes1 file
NOTICE:  2014-05-22 19:40:00.439189+01: Done staging Changes1 file
NOTICE:  2014-05-22 19:40:00.439379+01: Preparing to update localities
NOTICE:  2014-05-22 19:40:00.487656+01: Prepared 15 records for update on localities
NOTICE:  2014-05-22 19:40:00.489481+01: Removed 0 records from localities
NOTICE:  2014-05-22 19:40:00.504522+01: Created 15 records in localities
NOTICE:  2014-05-22 19:40:00.504651+01: Preparing to update thoroughfares
NOTICE:  2014-05-22 19:40:00.54741+01: Prepared 377 records for update on thoroughfares
NOTICE:  2014-05-22 19:40:00.548924+01: Removed 0 records from thoroughfares
NOTICE:  2014-05-22 19:40:00.589353+01: Created 377 records in thoroughfares
NOTICE:  2014-05-22 19:40:00.589477+01: Preparing to update thoroughfare_descriptor
NOTICE:  2014-05-22 19:40:00.631469+01: Prepared 0 records for update on thoroughfare_descriptor
NOTICE:  2014-05-22 19:40:00.632967+01: Removed 0 records from thoroughfare_descriptor
NOTICE:  2014-05-22 19:40:00.633275+01: Created 0 records in thoroughfare_descriptor
NOTICE:  2014-05-22 19:40:00.633444+01: Preparing to update building_names
NOTICE:  2014-05-22 19:40:00.700856+01: Prepared 7947 records for update on building_names
NOTICE:  2014-05-22 19:40:00.704261+01: Removed 0 records from building_names
NOTICE:  2014-05-22 19:40:01.155068+01: Created 7947 records in building_names
NOTICE:  2014-05-22 19:40:01.155178+01: Preparing to update sub_building_names
NOTICE:  2014-05-22 19:40:01.223108+01: Prepared 7798 records for update on sub_building_names
NOTICE:  2014-05-22 19:40:01.226335+01: Removed 0 records from sub_building_names
NOTICE:  2014-05-22 19:40:01.669071+01: Created 7798 records in sub_building_names
NOTICE:  2014-05-22 19:40:01.675826+01: Begin staging Changes2 file
NOTICE:  2014-05-22 19:40:02.59217+01: Done staging Changes2 file
NOTICE:  2014-05-22 19:40:02.592303+01: Preparing to update mainfile
NOTICE:  2014-05-22 19:40:05.07166+01: Prepared 216438 records for update on mainfile
NOTICE:  2014-05-22 19:41:41.439761+01: Removed 87291 records from mainfile
NOTICE:  2014-05-22 19:42:54.976222+01: Created 129147 records in mainfile
NOTICE:  2014-05-22 19:42:54.97639+01: Preparing to update organisations
NOTICE:  2014-05-22 19:42:55.609607+01: Prepared 65158 records for update on organisations
NOTICE:  2014-05-22 19:43:07.778516+01: Removed 32840 records from organisations
NOTICE:  2014-05-22 19:43:10.141383+01: Created 32318 records in organisations
NOTICE:  2014-05-22 19:43:10.18821+01: Begin staging WChanges file
NOTICE:  2014-05-22 19:43:10.218245+01: Done staging WChanges file
NOTICE:  2014-05-22 19:43:10.218346+01: Preparing to update welsh mainfile
NOTICE:  2014-05-22 19:43:10.311915+01: Prepared 8395 records for update on welsh mainfile
NOTICE:  2014-05-22 19:43:20.631738+01: Removed 3098 records from welsh mainfile
NOTICE:  2014-05-22 19:43:23.616801+01: Created 5149 records in welsh mainfile
NOTICE:  2014-05-22 19:43:23.61696+01: Preparing to update welsh organisations
NOTICE:  2014-05-22 19:43:23.624131+01: Prepared 0 records for update on welsh organisations
NOTICE:  2014-05-22 19:43:23.624836+01: Removed 0 records from welsh organisations
NOTICE:  2014-05-22 19:43:23.625512+01: Created 0 records in welsh organisations
NOTICE:  2014-05-22 19:43:23.634001+01: Begin staging postzon
NOTICE:  2014-05-22 19:43:29.097317+01: Done staging postzon file, now staging with lat long data
NOTICE:  2014-05-22 19:44:41.996743+01: Done staging postzon with lat long data, updating
NOTICE:  2014-05-22 19:44:57.195802+01: Inserted 3594 new records for update on postzon_100m
NOTICE:  2014-05-22 19:46:13.242174+01: Updated 212398 records for update on postzon_100m
NOTICE:  2014-05-22 19:46:24.038271+01: Deleted 3991 records for update on postzon_100m
NOTICE:  2014-05-22 19:46:24.808325+01: Begin staging alias file
NOTICE:  2014-05-22 19:46:32.810242+01: Done staging alias file
NOTICE:  2014-05-22 19:46:34.021948+01: Done staging counties , updating
NOTICE:  2014-05-22 19:46:34.023405+01: Inserted 0 new records for update on counties
NOTICE:  2014-05-22 19:46:34.024632+01: Updated 0 records for update on counties
NOTICE:  2014-05-22 19:46:34.025273+01: Deleted 0 records for update on counties
NOTICE:  2014-05-22 19:46:38.25488+01: Done staging county_alias , updating
NOTICE:  2014-05-22 19:46:41.711214+01: Inserted 3594 new records for update on county_alias
NOTICE:  2014-05-22 19:46:46.227681+01: Updated 12 records for update on county_alias
NOTICE:  2014-05-22 19:46:53.812323+01: Deleted 3991 records for update on county_alias
NOTICE:  2014-05-22 19:46:53.812483+01: Completed
 update_pc_paf
---------------
 t
(1 row)

My schema for the PAF data has deferrable foreign keys, and in order to apply the updates in chunks I’ve set them as deferred in the above function; I only find out if I’ve violated them when they’re checked on commit:

TEST=# COMMIT;

…. And it just sits there forever! I go and do something else, but when I come back it’s still sitting there; what did I forget?

Well we can make a pretty good guess that we’re waiting whilst the deferred constraints are checked, but the constraint checks don’t take that long when they’re not deferred so why is it taking so long?

Well it turns out I’ve got indexes on the satellite tables that are referenced by the foreign keys on my main address table, but no indexes for those keys on the actual main address table. It’s apparent that when the deferred constraint is checked it needs to look up the row first; something that wouldn’t have been required if the constraint were immediate. I add some indexes, and try again:

TEST=# COMMIT;
Time: 281979.437 ms

It worked, and we didn’t violate any constraints!

The new script (named paf_postgresql_import_postgis.plpgsql) is in the git repository at postgresql/geographic_data (mirrored also on github glynastill/geographic_data).

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