Re: BUG #15552: Unexpected error in COPY to a foreign table in atransaction

Hi,

On 2018/12/14 19:42, PG Bug reporting form wrote:
> The following bug has been logged on the website:
> 
> Bug reference:      15552
> Logged by:          Luis M Carril
> Email address:      luis.carril@swarm64.com
> PostgreSQL version: 11.1
> Operating system:   Ubuntu 16.04
> Description:        
> 
> Hi,
>    Postgres throws a "could not open file" error when inside a transaction
> we create a foreign table and copy data into it.
> 
> Reproduction (code based on tests in postgres_fdw test suite):
> -----------------------
> CREATE EXTENSION postgres_fdw;
> 
> CREATE SERVER testserver1 FOREIGN DATA WRAPPER postgres_fdw;
> DO $d$
>     BEGIN
>         EXECUTE $$CREATE SERVER loopback FOREIGN DATA WRAPPER postgres_fdw
>             OPTIONS (dbname '$$||current_database()||$$',
>                      port '$$||current_setting('port')||$$'
>             )$$;
>         EXECUTE $$CREATE SERVER loopback2 FOREIGN DATA WRAPPER
> postgres_fdw
>             OPTIONS (dbname '$$||current_database()||$$',
>                      port '$$||current_setting('port')||$$'
>             )$$;
>     END;
> $d$;
> 
> CREATE USER MAPPING FOR public SERVER testserver1
>     OPTIONS (user 'value', password 'value');
> CREATE USER MAPPING FOR CURRENT_USER SERVER loopback;
> 
> create table loct1 (a int check (a in (1)), b text);
> 
> begin;
> create foreign table remp1 (a int check (a in (1)), b text) server loopback
> options (table_name 'loct1');
> copy remp1 from stdin delimiter ',';
> 1,f
> \.
> -----------------------
> 
> Observed behavior:
>      ERROR:  could not open file "base/16385/16460": No such file or
> directory
> 
> -----------------------

Thanks for the report.  I can reproduce this both in 11 stable branch and
in HEAD.

> For what I saw, the error is triggered when synchronizing the heap in
> CopyFrom (backend/commands/copy.c:2890), see the following stacktrace (when
> setting a breakpoint at errcode_for_file_access():
> 
> #0  errcode_for_file_access () at
> /build/postgresql-11-9gVVK7/postgresql-11-11.1/build/../src/backend/utils/error/elog.c:600
> #1  0x00005636212d33d2 in mdopen (reln=<optimized out>,
> forknum=forknum@entry=MAIN_FORKNUM, behavior=behavior@entry=1)
>     at
> /build/postgresql-11-9gVVK7/postgresql-11-11.1/build/../src/backend/storage/smgr/md.c:606
> #2  0x00005636212d3961 in mdopen (behavior=1, forknum=MAIN_FORKNUM,
> reln=0x563622ba8a88) at
> /build/postgresql-11-9gVVK7/postgresql-11-11.1/build/../src/backend/storage/smgr/md.c:922
> #3  mdnblocks (reln=0x563622ba8a88, forknum=MAIN_FORKNUM) at
> /build/postgresql-11-9gVVK7/postgresql-11-11.1/build/../src/backend/storage/smgr/md.c:875
> #4  0x00005636212d39b9 in mdimmedsync (reln=0x563622ba8a88,
> forknum=MAIN_FORKNUM) at
> /build/postgresql-11-9gVVK7/postgresql-11-11.1/build/../src/backend/storage/smgr/md.c:1033
> #5  0x000056362103257c in heap_sync (rel=0x7f0e3e681aa8) at
> /build/postgresql-11-9gVVK7/postgresql-11-11.1/build/../src/backend/access/heap/heapam.c:9408
> #6  0x0000563621115e89 in CopyFrom (cstate=cstate@entry=0x563622ba2040) at
> /build/postgresql-11-9gVVK7/postgresql-11-11.1/build/../src/backend/commands/copy.c:2890

[ ... ]

> If someone gives me a hint on the expected behavior here, I would gladly
> submit a patch myself.

heap_sync should only be called for relations that actually have files to
sync, which isn't true for foreign tables.  So, a simple relkind check
before calling heap_sync() in CopyFrom would suffice I think.  Although,
we might also need such a check higher up in CopyFrom where some
optimizations that are specific to "heap" relations are enabled.  For
example, this piece of code:

    if (cstate->rel->rd_rel->relkind != RELKIND_PARTITIONED_TABLE &&
        (cstate->rel->rd_createSubid != InvalidSubTransactionId ||
         cstate->rel->rd_newRelfilenodeSubid != InvalidSubTransactionId))
    {
        hi_options |= HEAP_INSERT_SKIP_FSM;
        if (!XLogIsNeeded())
            hi_options |= HEAP_INSERT_SKIP_WAL;
    }

Note here that we check that the relation being copied into is not a
partitioned table, because a partitioned table doesn't have storage itself.

Thanks,
Amit