Hi,
Thanks for all the useful info. I managed to set up hive concurrency using
Oracle Metastore for Hive. Had to modify hive-txn-schema-0.14.0.oracle.sql
script in order to drop the existing tables as I had created the metastore
with hive-schema-0.14.0.oracle.sql initially.
All the transactions seem to behave as expected (meaning conforming to
behaviour expected from an ACID compliant RDBMS). Except a question that
comes to mind with locking when deleting all rows from the table (as opposed
to truncating the table)
I created a test table
create table txtest (col1 int, col2 varchar(30)) clustered by (col1) into 10
buckets STORED AS orc TBLPROPERTIES('transactional'='true');
Inserted 10 rows and updatedstats
insert into table txtest values
(1,'a'),(2,'b'),(3,'c'),(4,'d'),(5,'e'),(6,'f'),(7,'f'),(8,'g'),(9,'h'),(10,
'i');
analyse table txtest compute statistics;
Updated three columns followed by a single column
update txtest set col2 = col2 where col1 in (1,3,5);
update txtest set col2 = 'row1' where col1 = 1;
>From another session looked at locks
show locks;
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
| lockid | database | table | partition | lock_state |
lock_type | transaction_id | last_heartbeat | acquired_at | user |
hostname |
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
| Lock ID | Database | Table | Partition | State | Type
| Transaction ID | Last Hearbeat | Acquired At | User | Hostname |
| 21 | oraclehadoop | txtest | NULL | ACQUIRED |
SHARED_WRITE | 6 | 1428525777008 | 1428525774206 | hduser
| rhes564 |
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
Now see what happens if we try to delete two different rows from two
different sessions concurrently (well almost)
Session 1
hive> delete from txtest where col1 = 10;
Session 2
delete from txtest where col1 = 4;
The locks are shown below
show locks;
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
| lockid | database | table | partition | lock_state |
lock_type | transaction_id | last_heartbeat | acquired_at | user |
hostname |
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
| Lock ID | Database | Table | Partition | State | Type
| Transaction ID | Last Hearbeat | Acquired At | User | Hostname |
| 23 | oraclehadoop | txtest | NULL | ACQUIRED |
SHARED_WRITE | 7 | 1428526836905 | 1428526833132 | hduser
| rhes564 |
| 24 | oraclehadoop | txtest | NULL | WAITING |
SHARED_WRITE | 8 | 1428526865246 | NULL | hduser
| rhes564 |
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
Now delete all rows from the table
hive> delete from txtest;
0: jdbc:hive2://rhes564:10010/default> show locks;
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
| lockid | database | table | partition | lock_state |
lock_type | transaction_id | last_heartbeat | acquired_at | user |
hostname |
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
| Lock ID | Database | Table | Partition | State | Type
| Transaction ID | Last Hearbeat | Acquired At | User | Hostname |
| 25 | oraclehadoop | txtest | NULL | ACQUIRED |
SHARED_WRITE | 9 | 1428527740870 | 1428527737658 | hduser
| rhes564 |
+----------+---------------+---------+------------+-------------+-----------
----+-----------------+-----------------+----------------+---------+--------
---+--+
The question I have is if we delete from the whole table it seems that
"only" one lock is applied to whole table. Does that mean a full table lock
rather that locks for every row deleted?
Thanks,
Mich Talebzadeh
http://talebzadehmich.wordpress.com
Author of the books "A Practitioner's Guide to Upgrading to Sybase ASE 15",
ISBN 978-0-9563693-0-7.
co-author "Sybase Transact SQL Guidelines Best Practices", ISBN
978-0-9759693-0-4
Publications due shortly:
Creating in-memory Data Grid for Trading Systems with Oracle TimesTen and
Coherence Cache
Oracle and Sybase, Concepts and Contrasts, ISBN: 978-0-9563693-1-4, volume
one out shortly
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