Submitted by: @hvlad

There is user report that some of many Firebird CS processes crashes when database is shutting down by DBA before sweep run.
The crashes relatively rare, once per few days or weeks.
The coredump contains following stack

#⁠0 0x00007f7f438c5d44 in TRA_detach_request (request=0x7f7f34a1dab0) at ../src/jrd/tra.cpp:208
#⁠1 0x00007f7f4380c30e in EXE_unwind (tdbb=0x7f7f41cfdb40, request=0x7f7f34a1dab0) at ../src/jrd/exe.cpp:1122
#⁠2 0x00007f7f437d5e44 in CMP_release (tdbb=0x7f7f41cfdb40, request=0x7f7f34a1dab0) at ../src/jrd/cmp.cpp:2483
#⁠3 0x00007f7f437d6ab0 in CMP_fini (tdbb=0x7f7f41cfdb40) at ../src/jrd/cmp.cpp:743
#⁠4 0x00007f7f43843c7d in shutdown_database (dbb=0x7f7f39f89d98, release_pools=true) at ../src/jrd/jrd.cpp:5953
#⁠5 0x00007f7f43847d41 in purge_attachment (tdbb=0x7f7f41cfdb40, attachment=0x7f7f39f83408, force_flag=true) at ../src/jrd/jrd.cpp:6458
#⁠6 0x00007f7f438537d2 in jrd8_detach_database (user_status=0x7f7f41cfdd70, handle=0x7f7f405d02b8) at ../src/jrd/jrd.cpp:2499
#⁠7 0x00007f7f4370edd8 in fb_ping (user_status=<value optimized out>, db_handle=<value optimized out>) at ../src/jrd/why.cpp:6119
#⁠8 0x00007f7f43842cba in (anonymous namespace)::attachmentShutdownThread (arg=<value optimized out>) at ../src/jrd/jrd.cpp:7503
#⁠9 0x00007f7f43706f10 in run (arg=0x7f7f2930a138) at ../src/jrd/ThreadStart.cpp:128
#⁠10 (anonymous namespace)::threadStart (arg=0x7f7f2930a138) at ../src/jrd/ThreadStart.cpp:139
#⁠11 0x00007f7f426ceaa1 in start_thread () from /lib64/libpthread.so.0
#⁠12 0x00007f7f4241bbcd in clone () from /lib64/libc.so.6

Coredump analisys show that system request (used in METD to query metadata) contains reference (req_transaction) to the
(most probably) already deallocated transaction.

Commits: 1a6bcde