Re: Error that shouldn't happen?

It appears to me you might be making this a lot more difficult than
necessary. Why not just pre-create the required partitions daily or weekly
or monthly? Or do you have a requirement that a new partition only be
created the first time it is required?

On Thu, May 18, 2017 at 3:31 PM, David G. Johnston <
david(dot)g(dot)johnston(at)gmail(dot)com> wrote:

> On Thu, May 18, 2017 at 1:18 PM, Rob Brucks <rob(dot)brucks(at)rackspace(dot)com>
> wrote:
>
>> According to this post, adding "if not exists" won't really help for race
>> conditions.
>>
>>
>>
>> "The bottom line is that CREATE TABLE IF NOT EXISTS doesn't pretend to
>>
>> handle concurrency issues any better than regular old CREATE TABLE,
>>
>> which is to say not very well." - Robert Haas
>>
>>
>>
>> https://www.postgresql.org/message-id/CA+TgmoZAdYVtwBfp1FL2s
>> MZbiHCWT4UPrzRLNnX1Nb30Ku3-gg(at)mail(dot)gmail(dot)com
>>
>>
>>
>> It still doesn't explain how the function got past creating the table,
>> but failed on the index. If another thread was also creating the table
>> then there should have been lock contention on the create table statement.
>>
>>
>>
> A​T1: Insert, failed, cannot find table
> AT2: Insert, failed, cannot find table
> BT2: Create Table, succeeds
> BT1: Create Table; fails, it exists now, if exists converts to a warning
> CT2: Create Index, succeeds
> CT1: Create Index, fails , hard error
> DT2: Insert, succeeds
> ​DT1: Never Happens
>
> What that post seems to be describing is that it is possible the "BT1"
> actually hard errors instead of just being converted into a notice. There
> is no statement visible action to show that interleave but there is an
> underlying race condition since both BT1 and BT2 are executing concurrently.
>
> In short even with IF NOT EXISTS you are not guaranteed to not fail. But
> at least IF NOT EXISTS makes the probability of not failing > 0. It
> doesn't handle the concurrency any better - but it does change the outcome
> in some of those less-than-ideally handled situations.
>
> David J.
>
>

--
Andrew W. Kerber

'If at first you dont succeed, dont take up skydiving.'