To retrieve domain model data from PostgreSQL, I sometimes select against a view rather than a table. I do this so that I can return as much information as possible in one query, rather than fire off multiple queries to resolve all relational dependencies. Mostly this is because there is a 1-to-1 relationship between tables, or they are lookup tables and I just need certain columns, etc. To prevent certain race conditions, one strategy I'm using is SELECT ... FOR SHARE/UPDATE queries. I'm wondering how these behave when we start using them against views.

Suppose we have two tables A and B, each with a column ID. Now, suppose we have a view AB that is a join operation between those two tables. Let's assume this is a Cartesian join:

    "A"."ID" AS "AID",
    "B"."ID" AS "BID"

If we then SELECT FOR UPDATE against AB what rows of what tables will get locked in the following instances?

  • SELECT * FROM "AB" WHERE "AB"."AID" = :ID1 AND "AB"."BID" = :ID2

1 Answer 1


Short answer

The following rows will be locked for update in the three cases:

  • a row with "ID" = :ID in table "A" and all rows in table "B"
  • a row with "ID" = :ID in table "B" and all rows in table "A"
  • a row with "ID" = :ID1 in table "A" and a row with "ID" = :ID2 in table "B"

The results are as one can expect after reading this statement in the documentation:

If a locking clause is applied to a view or sub-query, it affects all tables used in the view or sub-query.

How to test similar cases

Install the extension pgrowlocks..

create extension if not exists pgrowlocks;

Run two instances of psql. In the first one start a transaction and execute a query.

psql #1:


select *
from "AB"
where "AID" = 3 and "BID" = 103
for update;

You can see locked rows in the other instance of psql.

psql #2:

select * from pgrowlocks('"B"');

 locked_row | locker | multi |  xids   |     modes      |  pids
 (0,4)      |  88577 | f     | {88577} | {"For Update"} | {8068}
(1 row) 

Do not forget to close the transaction at the end (before a next test).

psql #1:


The first column of the above result is ctid. You can select the original row with the query:

select *
from "B"
where ctid = '(0,4)';
  • Thanks for the detailed answer, and yes it's as I expected. I couldn't find that note in the documentation, I must have been looking in the wrong place. I guess it's time to look into a more robust locking strategy, starting with research into posts like this: dba.stackexchange.com/questions/81791/…
    – e_i_pi
    Oct 25, 2017 at 0:10
  • 1
    @e_i_pi: you could use Advisory Locks instead of "real" locks if all your code can be changed to comply with that.
    – user1822
    Oct 25, 2017 at 6:13
  • @a_horse_with_no_name I was thinking more along the lines of having locking tables that 1-to-1 with the main table, and locking that instead. I've used that technique before with good results, and since my app is DDD, this should work well with aggregate roots.
    – e_i_pi
    Oct 25, 2017 at 7:49

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