[android help] Sqlite: cannot open file at line

This error happened occasionally when I did some user/stress test on Android. Files under /data disapppeared and system server crashed after this error occurred. I am curious about the name of database "contacts2.db-mj7742599A4". Normally it should be contacts2.db. What does "*.db-mj7742599A4" mean? Anyone can help please?

02-28 19:21:43.161   660   695 E SQLiteLog: (14) cannot open file at line 30174 of [00bb9c9ce4]
02-28 19:21:43.169   660   695 E SQLiteLog: (14) os_unix.c:30174: (2) open(/data/data/com.android.providers.contacts/databases/contacts2.db-mj7742599A4) - 

02-28 19:21:43.520   397   409 I am_crash: [660,android.process.acore,572933,android.database.sqlite.SQLiteCantOpenDatabaseException,unable to open database file (code 14),SQLiteConnection.java,-2]
02-28 19:21:43.536   397  5671 I am_crash: [397,system_server,-1,java.lang.IllegalArgumentException,NULL,StatFs.java,-2]

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