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如果你的 SQL 或系统突然 hang 了，很有可能是因为一个 session 阻塞了另一个 session，如何查询是否发生阻塞了呢？看看下面的 SQL吧。
select blocksession.sid as block_session_sid, blocksession.serial# as block_session_serial#, blocksession.username as block_session_username, blocksession.osuser as block_session_osuser, blocksession.machine as block_session_machine, blocksession.status as block_session_status, blockobject.object_name as blocked_table, waitsession.sid as wait_session_sid, waitsession.serial# as wait_session_serial#, waitsession.username as wait_session_username, waitsession.osuser as wait_session_osuser, waitsession.machine as wait_session_machine, waitsession.status as wait_session_statusfrom v$lock blocklock, v$lock waitlock, v$session blocksession, v$session waitsession, v$locked_object lockedobject, dba_objects blockobjectwhere blocklock.block = 1 and blocklock.sid != waitlock.sid and blocklock.id1 = waitlock.id1 and blocklock.id2 = waitlock.id2 and blocklock.sid = blocksession.sid and waitlock.sid = waitsession.sid and lockedobject.session_id = blocksession.sid and lockedobject.object_id = blockobject.object_id;如果上面的语句返回了结果，表明发生了阻塞，这个时候你可以把使用 blocksession 的程序停掉。如果还是不能解决问题，那只能让 DBA 帮你把 blocksession kill 掉，如何 kill 呢？ 试一试下面的语句吧。