Database

Configuration

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

If you do not have a configuration file, first open a terminal and execute:

./aion.sh -c

Note that you may need to add the seed nodes to the file before starting the kernel.

The current default database configuration is:

<db>
    <path>database</path>
    <vendor>leveldb</vendor>
    <enable_db_compression>false</enable_db_compression>
    <check_integrity>true</check_integrity> <!--version 0.2.6 and after-->
    <state-storage>FULL</state-storage> <!--version 0.2.8 and after-->
</db>

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Database location

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.

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Database type

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

The current vendor options are:

• leveldb
• h2
• rocksdb

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.

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Data compression

The enable_db_compression tag customizes the behavior of the database to turn on or off its internal compression implementation. Enabling compression will reduce the storage space required, but may increase execution times for the different operations reading and writing to the database.

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Data integrity

The check_integrity tag allows enabling and disabling the data integrity checks at the kernel startup.

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State database pruning

The state-storage tag allows setting the pruning mode for the state database. The options are:

• FULL mode disables state pruning.
• TOP mode stores the state only for the top 256 blocks. This mode limits sync to branching only within the stored blocks.
• SPREAD mode stores the state only for the top 128 blocks and at regular intervals, namely each block for which the number is a multiple of 10000. This mode provides all the functionality of a full node, but with significantly decreased storage at the minor cost of some additional computations.

The database can also be updated offline to the desired mode by running the command:

./aion.sh --state CHOSEN_MODE

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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
• pendingtxCache and pendingtxPool store permanent copies of pending transactions that the node received

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.

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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.

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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.