Thread: GIN code managing entry insertion not able to differentiate fresh and old indexes

Hi all,

While playing with the GIN code for an upcoming patch, I noticed that
when inserting a new entry in a new index, this code path is not able
to make the difference if the index is in a build state or not.
Basically, when entering in ginEntryInsert@gininsert.c GinBtree built
via ginPrepareEntryScan does not have its flag isBuild set up
properly. I think that it should be set as follows to let this code
path be aware that index is in build state:
btree.isBuild = (buildStats != NULL);

Note that the entry insertion code does nothing with isBuild yet, so
it does not really impact back-branches. However, if in the future we
fix a bug in this area and need to make distinction between a fresh
index and an old one well there will be problems. For those reasons,
this correctness fix should be perhaps master-only for now (perhaps
even 9.4 stuff as well).

Patch is attached.

Regards,
--
Michael

On Thu, Nov 20, 2014 at 5:22 PM, Michael Paquier
<michael.paquier@gmail.com> wrote:
> Patch is attached.
A cleaner fix may be btw to pass the build stats in
ginPrepareEntryScan and set the flag directly there.
-- 
Michael

On Thu, Nov 20, 2014 at 05:22:02PM +0900, Michael Paquier wrote:
> Hi all,
> 
> While playing with the GIN code for an upcoming patch, I noticed that
> when inserting a new entry in a new index, this code path is not able
> to make the difference if the index is in a build state or not.
> Basically, when entering in ginEntryInsert@gininsert.c GinBtree built
> via ginPrepareEntryScan does not have its flag isBuild set up
> properly. I think that it should be set as follows to let this code
> path be aware that index is in build state:
> btree.isBuild = (buildStats != NULL);
> 
> Note that the entry insertion code does nothing with isBuild yet, so
> it does not really impact back-branches. However, if in the future we
> fix a bug in this area and need to make distinction between a fresh
> index and an old one well there will be problems. For those reasons,
> this correctness fix should be perhaps master-only for now (perhaps
> even 9.4 stuff as well).

Where did we leave this?

--  Bruce Momjian  <bruce@momjian.us>        http://momjian.us EnterpriseDB
http://enterprisedb.com
 + Everyone has their own god. +

On Sat, Mar 21, 2015 at 7:27 AM, Bruce Momjian wrote:
> On Thu, Nov 20, 2014 at 05:22:02PM +0900, Michael Paquier wrote:
>> While playing with the GIN code for an upcoming patch, I noticed that
>> when inserting a new entry in a new index, this code path is not able
>> to make the difference if the index is in a build state or not.
>> Basically, when entering in ginEntryInsert@gininsert.c GinBtree built
>> via ginPrepareEntryScan does not have its flag isBuild set up
>> properly. I think that it should be set as follows to let this code
>> path be aware that index is in build state:
>> btree.isBuild = (buildStats != NULL);
>>
>> Note that the entry insertion code does nothing with isBuild yet, so
>> it does not really impact back-branches. However, if in the future we
>> fix a bug in this area and need to make distinction between a fresh
>> index and an old one well there will be problems. For those reasons,
>> this correctness fix should be perhaps master-only for now (perhaps
>> even 9.4 stuff as well).
>
> Where did we leave this?

I recall Heikki mentioning me that the code paths where
ginPrepareEntryScan is called do not make use of isBuild, so it does
not matter much now to not fix it... But *if* there is a new feature
implemented in gin that makes use of the flag isBuild there will be
problems, so I am of the opinion to push a fix for correctness.
-- 
Michael