Re: [Postgres-xc-general] Sequence handling in Postgres-XC

[Tatsuo I. <is...@po...>]

> I am sure you already know that a Postgres-XC cluster needs a unique GTM
> (global transaction manager) to feed global transaction ID values and
> global snapshots to each node of the cluster, the same GTM is used for the
> feed of sequence values in a global way.
> As a start if you want to have a look at how it is managed in XC, for the
> postgres backend side have a look at nextval_internal in
> src/backend/commands/sequence.c, we put in the PG code a hook called
> GetNextValGTM to get the next global sequence value from GTM. There are
> similar hooks for CREATE/ALTER/DROP SEQUENCE. All the backend-side client
> APIs related to GTM are located in src/backend/access/transam/gtm.c.
> 
> On the GTM side, I would recommend you to have a look at src/gtm/main,
> mainly gtm_seq.c which contains all the sequence-related APIs.
> Also, the message types exchanged between GTM and backend nodes are listed
> in src/include/gtm/gtm_msg.h. MSG_SEQUENCE_GET_NEXT is for example the
> message type used to get the next global value of a sequence. Look at how
> messages of this type are managed on backend and GTM side and you will
> understand easily the process flow.

Thanks for a quick response. I will take a look at the source code.
--
Tatsuo Ishii
SRA OSS, Inc. Japan
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