A Failed Attempt to Recover JATOS' H2 Database
Recently I was asked to help with a broken JATOS instance. The logs were full of error messages like
IOException occurred reading text org.hibernate.HibernateException: IOException occurred reading text
java.io.IOException: Block not found in id [1, -70, -16, 5, 7] [1.4.192/50] at org.h2.mvstore.StreamStore$Stream.read(StreamStore.java:514) ~[com.h2database.h2-1.4.192.jar:1.4.192]
java.lang.IllegalStateException: Reading from cache:nio:C:/jatos-2.2.4_win_java/database/jatos.mv.db failed; file length 868352 read length 98304 at 15183555 [1.4.192/1]
Doesn’t look nice, does it? Somehow the H2 database got corrupted.
Usually the H2 database JATOS is using as a default is very reliable and so far I’ve never had an incident where data were damaged.
Unfortunately in this case the experimenter running this JATOS had recently gathered some data and hadn’t backed them up. So the only hope to rescue those data was to try to recover from the corrupted database file.
Apparently H2 comes shipped with a recovery tool. I’ve never attempted a recovery so far.
First, one has to download the H2 .jar file with the same version as the one your JATOS is using. In my case it is JATOS 2.2.4 and this version uses H2 version 1.4.192. You can look up H2 version in JATOS’ build.sbt (and its history if you don’t use the current JATOS version). H2’s webpage provides only the latest version but you can find older ones in other places, e.g. on www.versioneye.com/search?q=h2.
Now to the database files: one can find them in the folder database within the JATOS folder. There are two files: jatos.mv.db and jatos.trace.db and both we need. I strongly advice not to attempt the recovery on the original database files. Copy them to some other place together with H2’s .jar file.
Now it was time to start the recovery. Since it is a .jar we need Java. Then it’s just:
java -cp h2*.jar org.h2.tools.Recover
It will find the database files if they are in the same folder.
Unfortunately the attempt was a failure in this case.
java -cp h2-1.4.192.jar org.h2.tools.Recover Exception in thread "main" java.lang.IllegalStateException: Reading from cache:nio:/h2_recover/jatos.mv.db failed; file length 868352 read length 128 at 21963215 [1.4.192/1] ... Caused by: java.io.EOFException at org.h2.mvstore.DataUtils.readFully(DataUtils.java:431) ... 15 more
The jatos.mv.db file itself seems to be corrupted. Nothing I can do here (as far as I know).
Some advice in the end. The cause for the database corruption here was likely a file access from the OS while JATOS was running. So, please
- do not copy the JATOS database files while JATOS is still running.
- do backup. To backup the database copy the /database folder in the JATOS folder to a safe place.