Re: Serializable Snapshot Isolation

On 17/09/10 01:35, Kevin Grittner wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>
>> The functions are well commented, but an overview at the top of
>> the file of all the hash tables and other data structures would be
>> nice. What is stored in each, when are they updated, etc.
>
> I moved all the structures from predicate.h and predicate.c to a new
> predicate_internal.h file and added comments. You can view its
> current contents here:
>
> http://git.postgresql.org/gitweb?p=users/kgrittn/postgres.git;a=blob;f=src/include/storage/predicate_internal.h;h=7cdb5af6eebdc148dd5ed5030847ca50d7df4fe8;hb=7f05b21bc4d846ad22ae8c160b1bf8888495e254
>
> Does this work for you?

Yes, thank you, that helps a lot.

So, the purpose of SerializableXidHash is to provide quick access to the
SERIALIZABLEXACT struct of a top-level transaction, when you know its
transaction id or any of its subtransaction ids. To implement the "or
any of its subtransaction ids" part, you need to have a SERIALIZABLEXID
struct for each subtransaction in shared memory. That sounds like it can
eat through your shared memory very quickly if you have a lot of
subtransactions.

Why not use SubTransGetTopmostTransaction() ?

--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com