Is the data in Level 0 of RocksDB stored in a single sorted order?

Translated
1

Note:
This topic has been translated from a Chinese forum by GPT and might contain errors.

Original topic: RocksDB中 Level 0层的数据是单一排序存储吗？

| username: alfred

【TiDB Usage Environment】Production\Testing Environment\POC
【TiDB Version】
【Encountered Issues】
【Reproduction Path】What operations were performed that led to the issue
【Issue Phenomenon and Impact】
【Attachments】

  • Relevant logs, configuration files, Grafana monitoring (https://metricstool.pingcap.com/)
  • TiUP Cluster Display information
  • TiUP Cluster Edit config information
  • TiDB-Overview monitoring
  • Corresponding module’s Grafana monitoring (if any, such as BR, TiDB-binlog, TiCDC, etc.)
  • Corresponding module logs (including logs from 1 hour before and after the issue)

If the question is related to performance optimization or troubleshooting, please download the script and run it. Please select all and copy-paste the terminal output results for upload.

2
| username: xfworld | Original post link

The data in level 0 and Immtable is consistent and unordered.

From level 0 to level 1, sorting and compression will be performed…

That is, the data in level 1 is ordered.

3
| username: forever | Original post link

Level0 is directly obtained by flushing the Immutable Memtable, and the K/V in the file will not be sorted.
For Level-0 files, RocksDB always selects all files for compaction because there may be key range overlaps between Level-0 files.
For Level-N (N>1) files, they are first sorted by file size (bubble sort), the largest file is selected, and the key range of this file is calculated. Using this range, Level-N+1 files are searched. The selected Level-N file and Level-N+1 files are used as input, and one or more new SST files are created in Level-N+1 as output.

4
| username: ddhe9527 | Original post link

Within L0, individual SST files are ordered internally, but there may be overlapping keys between SST files, so the data in L0 can be considered globally unordered.

5
| username: alfred | Original post link

The explanation is clear, thank you.

6
| username: system | Original post link

This topic was automatically closed 60 days after the last reply. New replies are no longer allowed.