malloc error

I’m beginning to experiment with this project—and am likely doing plenty of things wrong—but encountered a cryptic malloc error and program crash after using this library successfully for several experiments. I’m posting what information I have in case this experience represents a stability bug in the code. If it only reflects me using the library incorrectly, my apologies along with appreciation for any tips on better usage.

While ingesting data into an lmdbjava system, it worked successfully for the first 340,000 items ingested, then hard crashed with the following error:

java(7179,0x70001ee7e000) malloc: *** error for object 0x70001ee7cf70: pointer being freed was not allocated
java(7179,0x70001e275000) malloc: *** error for object 0x70001ee7cf70: pointer being freed was not allocated
java(7179,0x70001ee7e000) malloc: *** set a breakpoint in malloc_error_break to debug
java(7179,0x70001e275000) malloc: *** set a breakpoint in malloc_error_break to debug

There was no other error message; no stack trace, etc. Before the error, everything seemed to be working fine. Running this system with a different key/value store (instead of lmdbjava) has worked successfully for a very long time.

The program terminated immediately and ungracefully after printing this message. Some of the data on disk was created during an earlier run of my application which ingested some data (~300,000 key/value pairs) before being shut down normally. Then I restarted and ran the same ingest. My relevant code (in Scala) is below:

val env = org.lmdbjava.Env
    .create()
    .setMapSize(3000485760L)
    .setMaxDbs(32)
    .setMaxReaders(1024)
    .open(new File(path), MDB_WRITEMAP, MDB_NOSYNC, MDB_NOLOCK)

  val db = env.openDbi("foo", org.lmdbjava.DbiFlags.MDB_CREATE)

def persistSnapshot(id: MyID, atTime: Milliseconds, state: Array[Byte]): Future[Unit] = {
    val idBb = ByteBuffer.allocateDirect(id.array.length)
    idBb.put(id.array).flip()
    val stateBb = ByteBuffer.allocateDirect(state.length)
    stateBb.put(state).flip()
    Future(db.put(idBb, stateBb))
  }

  def getLatestSnapshot(id: MyID, upToTime: Option[Milliseconds]): Future[Option[(Milliseconds, Array[Byte])]] = Future{
    val tx = env.txnRead()
    val idBb: ByteBuffer = ByteBuffer.allocateDirect(id.array.length)
    idBb.put(id.array).flip()
    val result = Option(db.get(tx, idBb)).map(r => 0L -> r.array())
    tx.close()
    result
  }

[benalexau]

I just added a Verifier class (see issue #124)for the ByteBuffer buffer type.

You may like to try the 0.6.4-SNAPSHOT (see the Snapshot Repository) with PROXY_OPTIMAL and PROXY_SAFE to get some extra confidence things are working OK on your platform.

BTW thanks for logging this ticket, as it prompted the development of the Verifier. Hopefully it’ll save folks time in the future.

[benalexau]

Very pleased that you found a solution!

There isn’t much we can do on the Java side to catch a native library SIGSEGV. I think there’s probably more utility in providing an “environment verifier” within LmdbJava that executes a defined sequence of write-then-read operations with successively larger keys, values, transaction sizes and user-nominated durations. That way those suspecting platform bugs can invoke a local method to build confidence their platform is compatible.