‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐

On Monday, May 20, 2019 12:37 AM, John Fawcett via dovecot <dovecot@dovecot.org> wrote:

So looking into this with a postgresql databse to work with: the above query does not work. You have to specify either the column name or the constraint name that you expect to be violated in order for the update to take place.

With a map like this one you're using

map {
    pattern = shared/last-login/$user/$domain
    table = last_login
    value_field = last_login
    value_type = uint

    fields {
        username = $user
        domain = $domain
    }
}

there's no field name that is obviously the primary key. I've reworked the patch to use the postgres default primary key constraint name (tablename_pkey).

So as you mention the new query you adapted which includes the primary key works, I tested it manually against PostgreSQL 10.5.

The attached fix should work in that case, although I feel it's not general enough.

Unfortunately my compiling skills are quite poor and I did not manage to patch and recompile Dovecot on OpenBSD.

Do you think your patch will make it into the Dovecot code?

I feel confident that the patch works as the query has been manually verified and the code change is not complex to validate.

The last_login plugin does not work at the moment with PostgreSql and probably does not work with Sqlite, given that the only logic that tries an update when insert fails seems to be a MySQL specific extension to standard Sql. So I think that it's clear that support for PostgreSql and Sqlite  needs to be implemented. The same issue likely exist in other plugins too, for example expire.

My doubts are around the right solution to adopt. Initially I thought that there was a PostgreSql syntax similar to MySQL which could be easily added to the code, but closer inspection shows that the PostgreSql syntax requires specification of either a constraint name or the index column(s) for the primary/unique keys.

Constraint names are nowhere specified in the dictionary map syntax and it's not possible either to identify with 100% certainty the primary key column(s).

The solution I adopted in the latest version of the patch is to use the default primary key constraint name derived from the table name, but that won't help if people define custom constraint names. That may be an unlikely scenario so the fix is certainly better than AS-IS. However it is not perfect and added to that is the fact that the PostgreSql extension is available only from 9.5.

I have no issues to submit the patch officially, as long as Dovecot developers agree. However it may be worthwhile reflecting on a more structural change

1) logic which always tries to update and falls back to insert if the update fails (or viceversa) for all sql dictionaries.

2) updates to the map syntax so that either the constraint name or primary key columns can be specified.

Ideas are welcome.

John