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From Tatsuya Kawano <tatsuy...@snowcocoa.info>
Subject Re: Unique row ID constraint
Date Thu, 29 Apr 2010 08:33:59 GMT
Hi Stack and Ryan,

Thanks for your advices. I knew using row lock wasn't ideal, but I
couldn't find an appropriate atomic operation to do Compare And Swap.

So, thanks Stack for helping me to find it. I found
incrementColumnValue() atomic operation just works for me since it
automatically initializes the column value with 0 when the column
doesn't exist. I cat try to increment the column value by 1, and if it
returns 1, I can be sure that I'm the first one who has created the
column and row.

So, my updated code is much simpler and now lock-free.

===============================================
  def insert(table: HTable, put: Put): Unit = {
    val count = table.incrementColumnValue(put.getRow, family, uniqueQual, 1)

    if (count == 1) {
      table.put(put)

    } else {
      throw new DuplicateRowException("Tried to insert a duplicate row: "
              + Bytes.toString(put.getRow))
    }
  }
===============================================

Thanks,
Tatsuya



2010/4/29 Ryan Rawson <ryanobjc@gmail.com>:
> I would strongly discourage people from building on top of
> lockRow/unlockRow.  The problem is if a row is not available, lockRow
> will hold a responder thread and you can end up with a deadlock
> because the lock holder won't be able to unlock.  Sure the expiry
> system kicks in, but 60 seconds is kind of infinity in database terms
> :-)
>
> I would probably go with either ICV or CAS to build the tools you
> want.  With CAS you can accomplish a lot of things locking
> accomplishes, but more efficiently.
>
> On Wed, Apr 28, 2010 at 9:42 AM, Stack <stack@duboce.net> wrote:
>> Would the incrementValue [1] work for this?
>> St.Ack
>>
>> 1. http://hadoop.apache.org/hbase/docs/r0.20.3/api/org/apache/hadoop/hbase/client/HTable.html#incrementColumnValue%28byte[],%20byte[],%20byte[],%20long%29
>>
>> On Wed, Apr 28, 2010 at 7:40 AM, Tatsuya Kawano
>> <tatsuyaml@snowcocoa.info> wrote:
>>> Hi,
>>>
>>> I'd like to implement unique row ID constraint (like the primary key
>>> constraint in RDBMS) in my application framework.
>>>
>>> Here is a code fragment from my current implementation (HBase
>>> 0.20.4rc) written in Scala. It works as expected, but is there any
>>> better (shorter) way to do this like checkAndPut()?  I'd like to pass
>>> a single Put object to my function (method) rather than passing rowId,
>>> family, qualifier and value separately. I can't do this now because I
>>> have to give the rowLock object when I instantiate the Put.
>>>
>>> ===============================================
>>> def insert(table: HTable, rowId: Array[Byte], family: Array[Byte],
>>>                               qualifier: Array[Byte], value:
>>> Array[Byte]): Unit = {
>>>
>>>    val get = new Get(rowId)
>>>
>>>    val lock = table.lockRow(rowId) // will expire in one minute
>>>    try {
>>>      if (table.exists(get)) {
>>>        throw new DuplicateRowException("Tried to insert a duplicate row:
"
>>>                + Bytes.toString(rowId))
>>>
>>>      } else {
>>>        val put = new Put(rowId, lock)
>>>        put.add(family, qualifier, value)
>>>
>>>        table.put(put)
>>>      }
>>>
>>>    } finally {
>>>      table.unlockRow(lock)
>>>    }
>>>
>>> }
>>> ===============================================
>>>
>>> Thanks,
>>>
>>> --
>>> 河野 達也
>>> Tatsuya Kawano (Mr.)
>>> Tokyo, Japan
>>>
>>> twitter: http://twitter.com/tatsuya6502

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