Files

In IoTDB, there are many kinds of data needed to be stored. This section introduces IoTDB's data storage strategy to provide you an explicit understanding of IoTDB's data management.

The data in IoTDB is divided into three categories, namely data files, system files, and pre-write log files.

Data Files

under directory basedir/data/

Data files store all the data that the user wrote to IoTDB, which contains TsFile and other files. TsFile storage directory can be configured with the data_dirs configuration item (see file layer for details). Other files can be configured through data_dirs configuration item (see Engine Layer for details).

In order to support users' storage requirements such as disk space expansion better, IoTDB supports multiple file directories storage methods for TsFile storage configuration. Users can set multiple storage paths as data storage locations( see data_dirs configuration item), and you can specify or customize the directory selection strategy (see multi_dir_strategy configuration item for details).

TsFile

under directory data/sequence or unsequence/{DatabaseName}/{DataRegionId}/{TimePartitionId}/

1. {time}-{version}-{inner_compaction_count}-{cross_compaction_count}.tsfile
   • normal data file
2. {TsFileName}.tsfile.mod
   • modification file
   • record delete operation

TsFileResource

1. {TsFileName}.tsfile.resource
   • descriptor and statistic file of a TsFile

Compaction Related Files

under directory basedir/data/sequence or unsequence/{DatabaseName}/

1. file suffixe with .cross or .inner
   • temporary files of metadata generated in a compaction task
2. file suffixe with .inner-compaction.log or .cross-compaction.log
   • record the progress of a compaction task
3. file suffixe with .compaction.mods
   • modification file generated during a compaction task
4. file suffixe with .meta
   • temporary files of metadata generated during a merge

System files

System files include schema files, which store metadata information of data in IoTDB. It can be configured through the base_dir configuration item (see System Layer for details).

MetaData Related Files

under directory basedir/system/schema

Meta

1. mlog.bin
   • record the meta operation
2. mtree-1.snapshot
   • snapshot of metadata
3. mtree-1.snapshot.tmp
   • temp file, to avoid damaging the snapshot when updating it

Tags&Attributes

1. tlog.txt
   • store tags and attributes of each TimeSeries
   • about 700 bytes for each TimeSeries

Other System Files

Version

under directory basedir/system/database/{DatabaseName}/{TimePartitionId} or upgrade

1. Version-{version}
   • version file, record the max version in fileName of a storage group

Upgrade

under directory basedir/system/upgrade

1. upgrade.txt
   • record which files have been upgraded

Authority

under directory basedir/system/users/
under directory basedir/system/roles/

CompressRatio

under directory basedir/system/compression_ration

1. Ration-{compressionRatioSum}-{calTimes}
   • record compression ratio of each tsfile

Pre-write Log Files

Pre-write log files store WAL files. It can be configured through the wal_dir configuration item (see System Layer for details).

under directory basedir/wal

1. {DatabaseName}-{TsFileName}/wal1
   • every storage group has several wal files, and every memtable has one associated wal file before it is flushed into a TsFile

Example of Setting Data storage Directory

For a clearer understanding of configuring the data storage directory, we will give an example in this section.

The data directory path included in storage directory setting are: base_dir, data_dirs, multi_dir_strategy, and wal_dir, which refer to system files, data folders, storage strategy, and pre-write log files.

An example of the configuration items are as follows:

dn_system_dir = $IOTDB_HOME/data/datanode/system
dn_data_dirs = /data1/datanode/data, /data2/datanode/data, /data3/datanode/data 
dn_multi_dir_strategy=MaxDiskUsableSpaceFirstStrategy
dn_wal_dir= $IOTDB_HOME/data/datanode/wal

After setting the configuration, the system will:

• Save all system files in $IOTDB_HOME/data/datanode/system
• Save TsFile in /data1/datanode/data, /data2/datanode/data, /data3/datanode/data. And the choosing strategy is MaxDiskUsableSpaceFirstStrategy, when data writes to the disk, the system will automatically select a directory with the largest remaining disk space to write data.
• Save WAL data in $IOTDB_HOME/data/datanode/wal