truncate table getting blocked

[Jayadevan M <maymala.jayadevan@xxxxxxxxx>]

Hello,

I have a python script. It opens a cursor, and sets the search_path (using psycopg2). In case something goes wrong in the script , a record is inserted into a table. In that script, I am not doing any thing else other than reading a file and publishing the lines to a queue (no database operations). The database is used just to track the errors. But my set search_path is locking a truncate table I am executing from a psql session. Is this expected?

When the truncate table hung, I used this query 

 SELECT blocked_locks.pid     AS blocked_pid,

         blocked_activity.usename  AS blocked_user,

         blocking_locks.pid     AS blocking_pid,

         blocking_activity.usename AS blocking_user,

         blocked_activity.query    AS blocked_statement,

         blocking_activity.query   AS current_statement_in_blocking_process

   FROM  pg_catalog.pg_locks         blocked_locks

    JOIN pg_catalog.pg_stat_activity blocked_activity  ON blocked_activity.pid = blocked_locks.pid

    JOIN pg_catalog.pg_locks         blocking_locks 

        ON blocking_locks.locktype = blocked_locks.locktype

        AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE

        AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation

        AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page

        AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple

        AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid

        AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid

        AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid

        AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid

        AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid

        AND blocking_locks.pid != blocked_locks.pid

   JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid

   WHERE NOT blocked_locks.GRANTED;

and got this (schemaname/user/tablename modified)- 

blocked_pid | blocked_user | blocking_pid | blocking_user |        blocked_statement         | current_statement_in_blocking_process 

-------------+--------------+--------------+---------------+----------------------------------+---------------------------------------

        9223 | myuser       |        12861 | myuser      | truncate table myschema.table1; | SET search_path TO  myschema,public 

PG version :

PostgreSQL 9.4.5 on x86_64-suse-linux-gnu, compiled by gcc (SUSE Linux) 4.8.5, 64-bit

Thanks,

Jayadevan