Trace file locks

In order to detect locking problems in multi-user applications, file locks may be traced. In order to trace file locks, the option

• TraceLocks=YES

has to be set to true (YES). File locks are written to the directory referenced in the TRACE option;

%TRACE%/userName_processID.lck

Since lock trace files may become very large, trace information is stored as binary data with the following structure:

struct _LockTrace {

DateTime timestamp; // lock/unlock time

int64position;// file position

int32length;// lock length

char operation; // +: lock, -: unlock

};

In order to keep lock files small, the lock file directory should refer to users home directory.

In order to analyze lock data, a lock trace database may be created by loading single files of all lock trace files (*.lck) in a directory (see example below).In order to run the analysis, naming conventions as described above, are required. The procedure creates an import database with two extents:

ObjectLocks: contains locks for each process

int32 pid; // process id

STRING(20)user;// file name without extension

SET<ObjectLock> locks; // locks for this process

ObjectLock contains all locks/unlocks

int32 pid; // process id

STRING(20)user;// file name without extension

DateTimetimestamp; // last lock/unlock time for position

int64 position;// file position

int32 length;// lock length

int32 cnt; // number of currently active locks

When importing lock trace files, a lock summary record is created for pid, position and length. The cnt field contains the number of currently active locks for the file lock in the current process.

In order to select locks for a certain time interval and a specific file position, the ObjectLock::List function may be called, which creates a result file in the TRACE directory (directory defined in the TRACE option).