# Consistency checker

# How do you run it?

It is part of immudb, enabled by default and runs as a thread of immudb. The routine can be disabled as follows:

./immudb --consistency-check=false

# What does it check?

Consistency checker runs in a loop and continuously checks if the elements stored inside the immudb Merkle-tree are also physically stored correctly on the disk (the digest of the disk elements is the same digest stored in the related Merkle-tree leaf)

# How does it run its check?

# Steps:

  1. reading the last root and last index stored in immudb
  2. generate a range between 0 and the length of the Merkle-tree level 0 (total number of elements stored)
  3. shuffles the range to get a random scan list (to be unpredictable)
  4. check if every element is correctly inserted in the Merkle-tree and if the Merkle-tree leaves correctly represent the elements stored on hard disk
  5. after completing the loop, the process sleeps ten seconds and restarts from scratch with a new root and index
  6. in case an element does not pass the check correctly, immudb is immediately stopped and prints out a log message

In order to produce a corrupted entry that is only on disk and not in the Merkle-tree, stop the immudb process and use the nimmu (opens new window) command:

go build tools/nimmu/nimmu.go 
./nimmu rawset key1 tamper

Then restart immudb and should see the consistency check printing an error.