[pgpool-hackers: 4336] Re: Allow to load balance PREPARE

[Tatsuo Ishii]

> Currently it is not possible load balance PREPARE even if the prepared
> query is read only SELECT. For example,
> 
> PREPARE foo AS SELECT 1;
> 
> is always sent to primary node (in streaming replication mode or
> logical replication mode), or main node (in other mode).
> 
> Attached patch is trying to load balance PREPARE (and following
> EXECUTE/DEALLOCATE). Documentation changes are not included yet.
> 
> For this following changes are made:
> 
> - is_select_query() looks into "query" member if node is
>   PrepareStmt. Also second argument "sql" (query string) is now
>   mandatory. If sql is NULL, warning is emitted and this function
>   returns false. If allow_sql_comments is off and node is PrepareStmt
>   and query is SelectStmt, is_select_query() does not return false
>   anymore.
> 
> - pool_has_function_call() looks into "query" member if node is
>   PrepareStmt.
> 
> - Add PREPARE/EXECUTE/DEALLOCATE test cases to 001.load_balance test.
> 
> - Add send_prepare() function which is similar to parse_before_bind in
>   extended query protocol case to keep up
>   disable_load_balance_on_write rule. send_prepare() is called by
>   SimpleQuery() when EXECUTE message is sent by frontend in SL mode so
>   that it sends PREPARE message to primary node if it has not sent to
>   primary because of load balance.  Note that send_prepare() does
>   nothing if the clustering mode is other than SL mode. In native
>   replication mode or snapshot isolation mode, all backend has the
>   same data, and there's no point to keep up
>   disable_load_balance_on_write rule.
> 
> Comments/suggestions are welcome.

Patch pushd. Thanks!

Best reagards,
--
Tatsuo Ishii
SRA OSS LLC
English: http://www.sraoss.co.jp/index_en/
Japanese:http://www.sraoss.co.jp