Database

Configuration

The database configuration can be set from the config folder by editing the config.xml file.

If you have not generated a default configuration yet, first open a terminal and execute:

./aion.sh -c

The current default database configuration is:

<db>
    <path>database</path>
    <vendor>leveldb</vendor>
</db>

---

1. The path tag is used for setting the physical location on disk where data will be stored.

The path is relative with respect to the current folder.

For example if you set the path to <path>database</path>, it will create a new folder called database where it will store the data. If the path is set to <path>database/db1</path>, it will create two new folders called database inside the current folder and db1 inside the database folder. The data will be stored in db1.

When setting the path for the database please make sure that:

• Your application has writing privileges on that path.
• There is no other database (using a different vendor) already using the path.

---

2. The vendor tag is used for choosing the database driver/implementation.

The current vendor options are:

• leveldb
• h2

If you are changing vendors, you must either:

• delete/move the previous database folder

or

• changes the path of the database to a new valid location.

Additional configuration options in aion-v0.1.9 and later versions

Starting with version 0.1.9 you can edit the kernel configuration file to customize each of the following options:

<db>
    <path>database</path>
    <vendor>leveldb</vendor>
    <enable_heap_cache>true</enable_heap_cache>
    <enable_auto_commit>false</enable_auto_commit>
    <enable_db_cache>false</enable_db_cache>
    <enable_db_compression>false</enable_db_compression>
    <max_heap_cache_size>0</max_heap_cache_size>
</db>

3. The enable_heap_cache tag is used for telling the kernel to store data in a LRU in-memory cache for fast access when it is set to true or to not use the in-memory cache when it is set to false.
4. The enable_auto_commit tag is for customizing the behavior for commiting data to the database inside the code. When set to true changes are committed to the database directly. When set to false data is committed only when an explicit commit call is made by the code. Note that when enable_heap_cache = false by default enable_auto_commit = true regardless of the setting in the config file, since without the LRU cache, changes would be lost if not saved to the database.
5. The enable_db_cache and enable_db_compression tags customize the behaviour of the database to use or not use its internal caching and compression implementations.
6. The max_heap_cache_size tag customizes the behaviour of the LRU cache when enabled. When max_heap_cache_size = 0, the setting is interpreted as unlimited (depending on the memory availability). Otherwise the given number determines the maximum number of entries kept in the LRU cache.

---

Contents

The Aion blockchain data is stored in several folders each representing a key-value database:

• block and index store the information about mined blocks
• details and storage keep information on contract details and data storage
• state is used for the state trie
• transaction keeps the data related to transactions

When the program is started it will print out its topmost known block number. In the case of an empty database, this will be the genesis block with a message like:

INFO GEN - loaded genesis block <num=0, root=4f512c6f...>

For a database that has some stored data, the message will look something like the one below:

INFO GEN - loaded block <num=33, root=a9182787... l=32>

To check that data was correctly written to the database stop the program (Ctrl+C) and restart it (./aion.sh). Compare the starting block number between the two runs. If any blocks were mined or synchronized while the program was running, the block number at the start of the program should reflect this change.

---

Recovery

Aion already has some built-in methods for attempting to recover from corrupted data inside the database. If the logs show that database recovery is in progress, please allow the program to complete the recovery process.

If the recovery process failed, or you prefer to restart from genesis, do the following:

1. Delete the database folder.
2. Restart the program. It will automatically sync with the network and populate the database.

---

Submitting Issues

If you can replicate the issue you experienced please enable the debugging feature of the database by editing the config.xml file. Between the log tags update (or add) the following line <DB>DEBUG</DB>. After enabling the debug messages, run the program again and add the log information to the issue description.

If you cannot replicate the issue please submit the old log information.

When possible you can also add a copy of the corrupted database to the issue description.