On Wed, Sep 25, 2013 at 12:50 PM, Steven Schlansker <steven@likeness.com> wrote:
>
> On Sep 25, 2013, at 6:04 AM, Merlin Moncure <mmoncure@gmail.com> wrote:
>
>> On Tue, Sep 24, 2013 at 10:19 PM, François Beausoleil
>> <francois@teksol.info> wrote:
>>> Hi all!
>>>
>>> I import many, many rows of data into a table, from three or more computers, 4 times per hour. I have a primary
key,and the query I use to import the data is supposed to dedup before inserting, but I still get primary key
violations.
>>>
>>> The import process is:
>>>
>>> * Load CSV data into temp table
>>> * INSERT INTO dest SELECT DISTINCT (pkey) FROM temp WHERE NOT EXISTS(temp.pkey = dest.pkey)
>>>
>>> I assumed (erroneously) that this would guarantee no duplicate data could make it into the database. The primary
keyviolations are proving me wrong.
>>
>> Right. Transaction A and B are interleaved: they both run the same
>> check against the same id at the same time. Both checks pass because
>> neither transaction is committed. This problem is not solvable by
>> adjusting the isolation level.
>
> Are you sure that this is the case? It is my understanding that since 9.1 with SSI
(https://wiki.postgresql.org/wiki/SSI)if you set the transaction isolation level to SERIALIZABLE, this problem is
solved,as the insert will take a "predicate lock" and the other insert cannot succeed.
>
> We use this to detect / resolve concurrent inserts that violate primary keys and it works great.
>
> However in this case it probably doesn't help the OP because the cost of restarting the entire import is likely too
high.
ah, you're right!
merlin
