pg_dump - ERROR - PostgreSQL 9.2

Hi all,

*masterdb01 -> slave01 -> slave02 -> slave03*

*testmaster01 (Full copy from masterdb01)*

I'm trying to refresh my main DB, by running this command on my test server:

ssh postgres(at)slave02 "/usr/pgsql-9.2/bin/pg_dump
> --exclude-table-data='junk.*' --format=custom master_db_name" |
> /usr/pgsql-9.2/bin/pg_restore --dbname=master_db_name_temp --exit-on-error

But, I got the following error after few seconds:

pg_dump: Dumping the contents of table "invoices" failed: PQgetResult()
> failed.
> pg_dump: Error message from server: ERROR: canceling statement due to
> conflict with recovery
> DETAIL: User was holding a relation lock for too long.
> pg_dump: The command was: COPY dm.invoices (invoice_id, format_version,
> ts_issue, ts_ack, customer_id, code, tag, account_data, customer_data,
> invoice_data, invoice_items_data) TO stdout;

If I run the pg_dump from the MASTER DB, it runs ok. But as the DB is 2 TB,
I just can't let it coping from Production. It has to be from a slave
server (I've also tried to copy from another slave. I get the same error).

What am I doing wrong? How can I solve the problem?

** I've sent the same e-mail to pgsql-general*

Thanks;
Lucas