Re: INSERT...ON DUPLICATE KEY LOCK FOR UPDATE

On Thu, Jan 2, 2014 at 11:08 AM, Heikki Linnakangas
<hlinnakangas(at)vmware(dot)com> wrote:
> On 01/02/2014 02:53 PM, Robert Haas wrote:
>> On Tue, Dec 31, 2013 at 4:12 AM, Peter Geoghegan <pg(at)heroku(dot)com> wrote:
>>>
>>> On Tue, Dec 31, 2013 at 12:52 AM, Heikki Linnakangas
>>> <hlinnakangas(at)vmware(dot)com> wrote:
>>>>
>>>> 1. PromiseTupleInsertionLockAcquire(<my xid>)
>>>> 2. Insert heap tuple
>>>> 3. Insert index tuples
>>>> 4. Check if conflict happened. Kill the already-inserted tuple on
>>>> conflict.
>>>> 5. PromiseTupleInsertionLockRelease(<my xid>)
>>>>
>>>> IOW, the only change to the current patch is that you acquire the new
>>>> kind
>>>> of lock before starting the insertion, and you release it after you've
>>>> killed the tuple, or you know you're not going to kill it.
>>>
>>>
>>> Where does row locking fit in there? - you may need to retry when that
>>> part is incorporated, of course. What if you have multiple promise
>>> tuples from a contended attempt to insert a single slot, or multiple
>>> broken promise tuples across multiple slots or even multiple commands
>>> in the same xact?
>
> You can only have one speculative insertion in progress at a time. After
> you've done all the index insertions and checked that you really didn't
> conflict with anyone, you're not going to go back and kill the tuple
> anymore. After that point, the insertion is not speculation anymore.

Yeah... but how does someone examining the tuple know that? We need
to avoid having them block on the promise-tuple insertion lock if
we've reacquired it meanwhile for a new speculative insertion.

--
Robert Haas
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