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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Update of "Hive/Locking" by NamitJain
Date Wed, 05 May 2010 17:34:25 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification.

The "Hive/Locking" page has been changed by NamitJain.
http://wiki.apache.org/hadoop/Hive/Locking?action=diff&rev1=17&rev2=18

--------------------------------------------------

  = Use Cases =
  
- Concurrency support (http://issues.apache.org/jira/browse/HIVE-1293) is a must in databases
and their usecases are well understood. At a minimum, we want to support concurrent readers
and writers whenever possible.
+ Concurrency support (http://issues.apache.org/jira/browse/HIVE-1293) is a must in databases
and their use cases are well understood. At a minimum, we want to support concurrent readers
and writers whenever possible.
  It would be useful to add a mechanism to discover the current locks which have been acquired.
There is no immediate requirement to add an API to explicitly acquire any locks, so all locks
would be acquired implicitly.
  
- The following lock modes are defined in hive (Note that Intent lock is not needed).
+ The following lock modes will be defined in hive (Note that Intent lock is not needed).
  
   * Shared    (S)
   * Exclusive (X)
  
  As the name suggests, multiple shared locks can be acquired at the same time, whereas X
lock blocks all other locks.
  
- The compatiblity matrix is as follows:
+ The compatibility matrix is as follows:
  
  ||''' ''' ||'''Existing Lock''' ||'''S''' ||'''X''' ||
  ||'''Requested Lock''' ||''' ''' ||''' ''' ||''' ''' ||
  ||'''S''' ||''' ''' ||'''True''' ||'''False''' ||
  ||'''X''' ||''' ''' ||'''False''' ||'''False''' ||
  
- For some operations, locks are hierarchial in nature - for eg. for some partition operations,
the table
+ For some operations, locks are hierarchical in nature - for eg. for some partition operations,
the table
  is also locked (for eg. to make sure that the table cannot be dropped while a new partition
is being created)
  
  The rational behind the lock mode to acquire is as follows:
@@ -68, +68 @@

  
  Two new configurable parameters will be added to decide the number of retries for the lock
and the 
  wait time between each retry. If the number of retries are really high, it can lead to a
live lock.
- Look at ZooKeeper (http://hadoop.apache.org/zookeeper/docs/r3.1.2/recipes.html#sc_recipes_Locks)
to
+ Look at ZooKeeper recipes (http://hadoop.apache.org/zookeeper/docs/r3.1.2/recipes.html#sc_recipes_Locks)
to
  see how read/write locks can be implemented using the zookeeper apis. Note that instead
of waiting,
  the lock request will be denied. The existing locks will be released, and all of them will
be retried
  after the retry interval.

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