Thanks. What do you mean when you say the transaction starts automatically at (2)? Do you mean that you don't need to start a transaction explicitly?
If that's right, does that mean that you need to commit even after you've only done read operations, so that Phoenix knows to close the transaction it's created for you? James On 28 July 2016 11:45:17 p.m. James Taylor <[email protected]> wrote: James, Your logic looks correct, assuming that you have the complete row keys in your SELECT statement. FYI, the transaction will start automatically at (2). You can optimize this slightly by just doing a COUNT(*) instead of returning the rows back to the client. For the UPDATE case, you'd throw if the count doesn't match the number of rows you have. You'll also have the added benefit that another client attempting to INSERT or UPDATE the same rows at the same time would fail (that's the conflict detection piece that Thomas mentioned). Thanks, James On Thu, Jul 28, 2016 at 2:46 PM, Thomas D'Silva <[email protected]<mailto:[email protected]>> wrote: If the table is transactional, you are guaranteed that if there are overlapping transactions that try to commit the same row one will succeed and the others will fail with an exception. There is also an additional cost to doing conflict detection at commit time. On Thu, Jul 28, 2016 at 8:18 AM, Heather, James (ELS) <[email protected]<mailto:[email protected]>> wrote: What would I need to do in order to emulate an INSERT or UPDATE in Phoenix, as opposed to an UPSERT? Suppose I had a TRANSACTIONAL table. To do an INSERT, I then: 1. Start a transaction 2. SELECT the relevant rows, and throw an error if the SELECT is non-empty 3. UPSERT 4. Commit the transaction To do an UPDATE, I do the same, except that in step 2 I throw an error if the SELECT is empty. If all of the possible writes to those rows are enclosed in transactions, will this avoid the race conditions and give me a true INSERT and UPDATE (at a cost of having to make multiple queries, of course)? The case I have in mind is where we might have DELETE and PATCH queries coming into our API. With a back end that supports UPDATE, it's not a problem if a DELETE and a PATCH come in at the same time: either the DELETE succeeds and then the PATCH fails, or the PATCH succeeds and then the DELETE succeeds. Either way, you end up with the row's being deleted. But if we use an UPSERT statement for the PATCH, we have a problem: the DELETE can succeed, and then the PATCH will still succeed, but it'll insert the row back in again. I'm unclear as to how to use transactions to guarantee the right behaviour here. James ________________________________ Elsevier Limited. Registered Office: The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, United Kingdom, Registration No. 1982084, Registered in England and Wales. ________________________________ Elsevier Limited. Registered Office: The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, United Kingdom, Registration No. 1982084, Registered in England and Wales.
