Created attachment 373036 [details]
Example Python script reproducing issue

I've been writing some integration tests which call the following code multiple times:

session = gnucash.Session('mysql://root:oxford@localhost/test', is_new=True, ignore_lock=False)
session.end()
session.destroy()

After this runs a large number of times I get an error 'Too many connections' because Gnucash is not closing the database connection when the session ends/is destroyed. The connections are only closed when the script finishes.

I think the problem might be that two database connections are originally opened, as if session.end()/session.destroy() is not called, two connections are created each time session = gnucash.Session is called, but only one is cleaned up by session.end()/session.destroy() leaving an additional connection open after this set of 3 commands.

Digging deeper, here's part of the MySQL query log for session = gnucash.Session

2018-10-24T13:00:10.997511Z     7 Connect   root@localhost on test using Socket
2018-10-24T13:00:10.997735Z     7 Query SET NAMES 'utf8'
2018-10-24T13:00:10.997937Z     7 Query SELECT @@sql_mode
2018-10-24T13:00:10.998749Z     7 Query SET sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'
2018-10-24T13:00:10.998934Z     7 Query CREATE TEMPORARY TABLE numtest ( test_int BIGINT, test_unsigned BIGINT, test_double FLOAT8 )
2018-10-24T13:00:11.000065Z     7 Query INSERT INTO numtest VALUES (-9223372036854775807, 9223372036854775807, 1.79769213486e+307)
2018-10-24T13:00:11.000440Z     7 Query SELECT * FROM numtest
2018-10-24T13:00:11.000777Z     7 Query DROP TABLE numtest
2018-10-24T13:00:11.028168Z     7 Query SHOW TABLES FROM `test`

2018-10-24T13:00:11.029106Z     8 Connect   root@localhost on test using Socket
2018-10-24T13:00:11.029276Z     8 Query SET NAMES 'utf8'
2018-10-24T13:00:11.029424Z     8 Query SELECT @@sql_mode
2018-10-24T13:00:11.029664Z     8 Query SET sql_mode='ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES,NO_ZERO_IN_DATE,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ENGINE_SUBSTITUTION'
2018-10-24T13:00:11.029780Z     8 Query CREATE TEMPORARY TABLE numtest ( test_int BIGINT, test_unsigned BIGINT, test_double FLOAT8 )
2018-10-24T13:00:11.030637Z     8 Query INSERT INTO numtest VALUES (-9223372036854775807, 9223372036854775807, 1.79769213486e+307)
2018-10-24T13:00:11.030847Z     8 Query SELECT * FROM numtest
2018-10-24T13:00:11.031036Z     8 Query DROP TABLE numtest

2018-10-24T13:00:11.032583Z     8 Query BEGIN
2018-10-24T13:00:11.032757Z     8 Query SHOW TABLES FROM `test` LIKE 'gnclock'
....

You can see that two connections are opened - 7 and 8, but connection 7 is never closed and they also run the conn_test_dbi_library functions twice.

I think this narrows the issue down to GncDbiBackend<Type>::session_begin in gnc-backend-dbi.cpp, specifically dbi_conn_connect is called twice in this function: once for the tests (connection 7 above) and once to create a new book (connection 8) - it's possible this issues exists outside of the Python bindings and is a bug in the DBI backend, but I haven't confirmed this though the GUI.

Please find a test script attached (which assumes MySQL credentials) which runs the above commands 5 times and counts the open connections after each run.

I hope this is enough to investigate the issue further, but if you have any other queries please let me know.

Kind regards,

Tom