Submitted by: @pavel-zotov

Environment:

1) database on LINUX server (host/port:database = 192.168.0.220/3333:/var/db/fb30/oltp30.fdb );
2) FB binaries, including fbsvcmgr, present on Windows machine which serves now as client;
3) time values on both machines are very close.

Consider batch that is launched on Windows machine:

@echo off
setlocal enabledelayedexpansion enableextensions
echo !time! starting ISQL...
echo select count(*) from rdb$types; | isql 192.168.0.220/3333:/var/db/fb30/oltp30.fdb -user sysdba -pas masterkey >nul
echo !time! return from ISQL, start small delay...
ping -n 3 127.0.0.1 >nul
echo !time! finish small delay, starting obtaining DB header info...
fbsvcmgr 192.168.0.220/3333:service_mgr -user SYSDBA -password masterkey action_db_stats sts_hdr_pages dbname /var/db/fb30/oltp30.fdb
echo !time! finish obtaining DB header info...

Before this batch will be run, start following .sh on Linux host:

log=./lsof_$(date +'%Y%m%d_%H%M%S').log
rm -f $log
while :
do
supertee -tan $log lsof /var/db/fb30/oltp30.fdb
sleep 0.5
done

-- and then run windows batch.

Log of .sh will be following:

[root@oel64 21:06:51 /var/db/fb30/logs]$ head -1 lsof_20151225_210630.log; grep -iv "COMMAND" lsof_20151225_210630.log
Fri Dec 25 21:06:35 2015: COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
Fri Dec 25 21:06:35 2015: firebird 15993 firebird 9u REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb
Fri Dec 25 21:06:35 2015: firebird 15993 firebird 9uW REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb
Fri Dec 25 21:06:36 2015: firebird 15993 firebird 9uW REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb
Fri Dec 25 21:06:36 2015: firebird 15993 firebird 9uW REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb
Fri Dec 25 21:06:37 2015: firebird 15993 firebird 9uW REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb
Fri Dec 25 21:06:37 2015: firebird 15993 firebird 9uW REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb --------- [ 1 ]
Fri Dec 25 21:06:38 2015: firebird 15993 firebird 9u REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb ----------- [ 2 ]
Fri Dec 25 21:06:39 2015: firebird 15993 firebird 9u REG 8,4 3510632448 6554793 /var/db/fb30/oltp30.fdb

Ouput of Windows batch will be:

21:06:33.71 starting ISQL...
21:06:34.85 return from ISQL, start small delay...
21:06:36.88 finish small delay, starting obtaining DB header info...
21:06:36.98 finish obtaining DB header info...

Between points [1] and [2] lock-state of database was changed from "9uW" to "9u".
It is "fbsvcmgr action_db_stats" command that was run on Windows host that lead to this change.

PS. LI-V3.0.0.32239

Commits: f4defcd 7b5b0ca FirebirdSQL/fbt-repository@5b5380b FirebirdSQL/fbt-repository@86f24cf

====== Test Details ======

Can be reproduced only on POSIX with scenario that is similar to:

@echo off
setlocal enabledelayedexpansion enableextensions
echo !time! starting ISQL...
echo select count(*) from rdb$types; | isql /3333:oltp30 -user sysdba
-pas masterkey >nul
echo !time! return from ISQL, start small delay...
ping -n 3 127.0.0.1 >nul
echo !time! finish small delay, starting obtaining DB header info...
fbsvcmgr /3333:service_mgr -user SYSDBA -password masterkey
action_db_stats sts_hdr_pages dbname oltp30
echo !time! finish obtaining DB header info...
nbackup -L oltp30
echo !time! get lock
nbackup -N oltp30
echo !time! free lock