PostgreSQL Unit Test – Deferrable Foreign Key with PgTap

ddlpostgresqlunit test

I am using PgTap to unit test a Postgres (v9.4) database structure in a continuous migration process. It works great.

Here is my question: « Is there a way to control that a foreign key constraint is deferrable (initially immediate) ? »

I do already check foreign keys but I want to ensure some of them are deferrable.

Thank you for your help.

Best Answer

Ok, it appears there are no methods to test such thing with PgTap for now so I ended up with

SELECT results_eq(
    $$select condeferrable, condeferred from pg_catalog.pg_constraint where conname = 'default_article_id_fk'$$,
    $$values ('t'::bool, 'f'::bool)$$,
    '"default_article_id_fk" is deferrable initially immediate.'
);

That does the job.

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Postgresql – Postgres multiple joins slow query, how to store default child record

You write:

Each customer can have multiple sites, but only one should be displayed in this list.

Yet, your query retrieves all rows. That would be a point to optimize. But you also do not define which site is to be picked.

Either way, it does not matter much here. Your EXPLAIN shows only 5026 rows for the site scan (5018 for the customer scan). So hardly any customer actually has more than one site. Did you ANALYZE your tables before running EXPLAIN?

From the numbers I see in your EXPLAIN, indexes will give you nothing for this query. Sequential table scans will be the fastest possible way. Half a second is rather slow for 5000 rows, though. Maybe your database needs some general performance tuning?

Maybe the query itself is faster, but "half a second" includes network transfer? EXPLAIN ANALYZE would tell us more.

If this query is your bottleneck, I would suggest you implement a materialized view.

After you provided more information I find that my diagnosis pretty much holds.

The query itself needs 27 ms. Not much of a problem there. "Half a second" was the kind of misunderstanding I had suspected. The slow part is the network transfer (plus ssh encoding / decoding, possibly rendering). You should only retrieve 100 rows, that would solve most of it, even if it means to execute the whole query every time.

If you go the route with a materialized view like I proposed you could add a serial number without gaps to the table plus index on it - by adding a column row_number() OVER (<your sort citeria here>) AS mv_id.

Then you can query:

SELECT *
FROM   materialized_view
WHERE  mv_id >= 2700
AND    mv_id <  2800;

This will perform very fast. LIMIT / OFFSET cannot compete, that needs to compute the whole table before it can sort and pick 100 rows.

pgAdmin timing

When you execute a query from the query tool, the message pane shows something like:

Total query runtime: 62 ms.

And the status line shows the same time. I quote pgAdmin help about that:

The status line will show how long the last query took to complete. If a dataset was returned, not only the elapsed time for server execution is displayed, but also the time to retrieve the data from the server to the Data Output page.

If you want to see the time on the server you need to use SQL EXPLAIN ANALYZE or the built in Shift + F7keyboard shortcut or Query -> Explain analyze. Then, at the bottom of the explain output you get something like this:

Total runtime: 0.269 ms

Postgresql – How to get a working and complete PostgreSQL DB backup and test

You can dump the whole PostgreSQL cluster with pg_dumpall. That's all the databases and all the globals for a single cluster. From the command line on the server, I'd do something like this. (Mine's listening on port 5433, not on the default port.) You may or may not need the --clean option.

$ pg_dumpall -U postgres -h localhost -p 5433 --clean --file=dump.sql

This includes the globals--information about users and groups, tablespaces, and so on.

If I were going to backup a single database and move it to a scratch server, I'd dump the database with pg_dump, and dump the globals with either

pg_dumpall --globals-only, or
pg_dumpall --roles-only (if you only need roles)

like this.

$ pg_dump -U postgres -h localhost -p 5433 --clean --file=sandbox.sql sandbox
$ pg_dumpall -U postgres -h localhost -p 5433 --clean --globals-only --file=globals.sql

Outputs are just text files.

After you move these files to a different server, load the globals first, then the database dump.

$ psql -U postgres -h localhost -p 5433 < globals.sql
$ psql -U postgres -h localhost -p 5433 < sandbox.sql

I thought pg_dumpall would at least backup foreign keys, but even that seems to be an 'option'. According to: http://www.postgresql.org/docs/9.1/static/app-pg-dumpall.html even with pg_dumpall I need to use a -o option to backup foreign keys

No, that reference says "Use this option if your application references the OID columns in some way (e.g., in a foreign key constraint). Otherwise, this option should not be used." (Emphasis added.) I think it's unlikely that your application references the OID columns. You don't need to use this option to "backup foreign keys". (Read the dump file in your editor or file viewer.)

Best Answer

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