[pgpool-committers: 9958] pgpool: Fix MAIN_NODE macro (actually pool_virtual_main_db_node_id()).

[Tatsuo Ishii]

Fix MAIN_NODE macro (actually pool_virtual_main_db_node_id()).

The macro used to REAL_MAIN_NODE_ID if there's no session context.
This is wrong since REAL_MAIN_NODE_ID can be changed any time when
failover/failback happens.  Suppose REAL_MAIN_NODE_ID ==
my_main_node_id == 1. Then due to failback, REAL_MAIN_NODE_ID is
changed to 0. Then MAIN_CONNECTION(cp) will return NULL and any
reference to it will cause segmentation fault. To prevent the issue we
should return my_main_node_id instead.

Discussion: https://www.pgpool.net/pipermail/pgpool-general/2024-June/009205.html
Backpatch-through: V4.1

Branch
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V4_5_STABLE

Details
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https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=85a5ba018cd1c5cbdd2ce9e66d6d68a70003ef93

Modified Files
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src/context/pool_query_context.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)