[pgpool-committers: 6953] pgpool: Add statistics for INSERT/UPDATE/DELETE etc. SQL commands.

[Tatsuo Ishii]

Add statistics for INSERT/UPDATE/DELETE etc. SQL commands.

We already allow to collect stats for SELECT, but it would be useful
to collect stats for other types of SQL commands. APIs to fetch stats
data is also added. No UI is added yet. Currently, any SQL commands
(besides SELECT/INSERT/UPDATE/DELETE) other than:

                        case(T_CheckPointStmt):
                        case(T_DeallocateStmt):
                        case(T_DiscardStmt):
                        case(T_ExecuteStmt):
                        case(T_ExplainStmt):
                        case(T_ListenStmt):
                        case(T_LoadStmt):
                        case(T_LockStmt):
                        case(T_NotifyStmt):
                        case(T_PrepareStmt):
                        case(T_TransactionStmt):
                        case(T_UnlistenStmt):
                        case(T_VacuumStmt):
                        case(T_VariableSetStmt):
                        case(T_VariableShowStmt):

are counted as DDL commands.
Discussion: https://www.pgpool.net/pipermail/pgpool-hackers/2020-July/003754.html

Branch
------
master

Details
-------
https://git.postgresql.org/gitweb?p=pgpool2.git;a=commitdiff;h=9f74a2281f6f10b5160051c8291713b9f5ed5205

Modified Files
--------------
src/include/utils/statistics.h |  5 +++
src/utils/statistics.c         | 72 ++++++++++++++++++++++++++++++++++++++++++
2 files changed, 77 insertions(+)