[pgpool-committers: 9400] pgpool: Allow to load balance PREPARE/EXECUTE/DEALLOCATE.

[Tatsuo Ishii]

Allow to load balance PREPARE/EXECUTE/DEALLOCATE.

Previously PREPARE/EXECUTE/DEALLOCATE are not load balanced. In
streaming replication/logical replication mode, they were sent to
always primary node. In native replication/snapshot isolation
mode,they were always sent to all nodes.

Now they can be load balanced if the SQL statement prepared by PREPARE
command is a read only SELECT.

For this purpose following changes were made:

- is_select_query() looks into "query" member if node is
  PrepareStmt. Also second argument "sql" (query string) is not 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.

- Remove descriptions of restrictions regarding load balance for
  PREPARE/EXECUTE/DEALLOCATE in "Restrictions" section in the docs.

Discussion: https://www.pgpool.net/pipermail/pgpool-hackers/2023-May/004334.html

Branch
------
master

Details
-------
https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=66fa78e2b5b97c116fce914f474ef562febbfa10

Modified Files
--------------
doc.ja/src/sgml/restrictions.sgml                  |   9 --
doc/src/sgml/restrictions.sgml                     |  10 --
src/context/pool_query_context.c                   |  19 ++-
src/protocol/pool_process_query.c                  |  33 +++--
src/protocol/pool_proto_modules.c                  | 134 +++++++++++++++++++++
.../tests/001.load_balance/expected/expected1-r    |   6 +
.../tests/001.load_balance/expected/expected1-s    |   4 +
.../tests/001.load_balance/expected/expected6-r    |  91 +++++++++++++-
.../tests/001.load_balance/expected/expected6-s    |  87 ++++++++++++-
.../tests/001.load_balance/expected/expected7-r    |   6 -
.../regression/tests/001.load_balance/sql/6.sql    |  27 +++++
src/test/regression/tests/001.load_balance/test.sh |  19 +--
src/utils/pool_select_walker.c                     |   7 ++
13 files changed, 402 insertions(+), 50 deletions(-)