When Admin/Posting/Manage Attachments is clicked, and there are attachments whose collective size exceeds 2.1 GB, it fails with this exception:

General Error

SQL ERROR [ mssqlnative ]

SQLSTATE: 22003 code: 8115 message: [Microsoft][ODBC Driver 13 for SQL Server][SQL Server]Arithmetic overflow error converting expression to data type int. [8115]

SQL

SELECT COUNT(a.attach_id) AS num_files, SUM(a.filesize) AS upload_dir_size FROM phpbb_attachments a WHERE a.is_orphan = 0

BACKTRACE

FILE: (not given by php)
LINE: (not given by php)
CALL: msg_handler()

FILE: [ROOT]/phpbb/db/driver/driver.php
LINE: 997
CALL: trigger_error()

FILE: [ROOT]/phpbb/db/driver/mssqlnative.php
LINE: 147
CALL: phpbb\db\driver\driver->sql_error()

FILE: [ROOT]/phpbb/db/driver/factory.php
LINE: 329
CALL: phpbb\db\driver\mssqlnative->sql_query()

FILE: [ROOT]/includes/acp/acp_attachments.php
LINE: 1298
CALL: phpbb\db\driver\factory->sql_query()

FILE: [ROOT]/includes/acp/acp_attachments.php
LINE: 1331
CALL: acp_attachments->get_attachment_stats()

FILE: [ROOT]/includes/acp/acp_attachments.php
LINE: 1133
CALL: acp_attachments->check_stats_accuracy()

FILE: [ROOT]/includes/functions_module.php
LINE: 676
CALL: acp_attachments->main()

FILE: [ROOT]/adm/index.php
LINE: 82
CALL: p_master->load_active()
 
 
The problem is that phpbb_attachments.filesize is an INT, with a maximum upper limit of 2,147,483,647. When attempting to SUM the filesizes column, MSSQL expects the result to also be an INT. The sum of those values exceeds the INT value, and results in an overflow.
 
Instead of this SQL:

SELECT COUNT(a.attach_id) AS num_files, SUM(a.filesize) AS upload_dir_size FROM phpbb_attachments a WHERE a.is_orphan = 0

Using this SQL would fix this problem:
 
SELECT COUNT(a.attach_id) AS num_files, SUM(CAST(a.filesize AS BIGINT)) AS upload_dir_size FROM phpbb_attachments a WHERE a.is_orphan = 0
 
This is in MSSQL - other SQL servers may have different limits on their INT values.