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 <ryano...@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 <st...@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
>> <tatsuy...@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
