docs/SystemDesign/StorageEngine/DataPartition.md

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# Data partition

Time series data is partitioned on two levels of storage groups and time ranges.

## Storage group

The storage group is specified by the user display. Use the statement "SET STORAGE GROUP TO" to specify the storage group. Each storage group has a corresponding StorageGroupProcessor.

The main fields it has are:

* Read-write lock: insertLock

* Unclosed sequential file processors for each time partition: workSequenceTsFileProcessors

* Unclosed out-of-order file processor corresponding to each time partition: workUnsequenceTsFileProcessors

* Full sequential file list for this storage group (sorted by time): sequenceFileTreeSet

* List of all out-of-order files for this storage group (unordered): unSequenceFileList

* A map that records the last write time of each device. When sequential data is flashed, the time recorded by this map is used: latestTimeForEachDevice

* A map that records the last flash time of each device to distinguish between sequential and out-of-order data: latestFlushedTimeForEachDevice

* A version generator map corresponding to each time partition, which is convenient for determining the priority of different chunks when querying: timePartitionIdVersionControllerMap


### Related code

* src/main/java/org/apache/iotdb/db/engine/StorageEngine.java


## Time range

The data in the same storage group is partitioned according to the time range specified by the user. The related parameter is partition_interval and the default is week. That is, data of different weeks will be placed in different partitions.

### Implementation logic

StorageGroupProcessor performs partition calculation on the inserted data to find the specified TsFileProcessor, and the TsFile corresponding to each TsFileProcessor will be placed in a different partition folder.

### File structure

The file structure after partitioning is as follows:

data

-- sequence

---- [Storage group name1]

------ [Time division ID1]

-------- xxxx.tsfile

-------- xxxx.resource

------ [Time division ID2]

---- [Storage group name 2]

-- unsequence

### Related code

* getOrCreateTsFileProcessorIntern  method in src/main/java/org/apache/iotdb/db/engine/storagegroup.StoragetGroupProcessor.java