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This topic has been translated from a Chinese forum by GPT and might contain errors.Original topic: 请问TIDB的索引结构是什么呢
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username: TiDBer_JlY1JCJ5
Is it also a B+Tree like MySQL?
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username: TiDBer_JlY1JCJ5
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username: 
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username: The underlying layer of TiDB is RocksDB, a KV database that uses the LSM-Tree data structure.
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username: Both business data and index data are converted into KV key-value pairs for storage. The underlying TiKV can be roughly understood as a huge Map structure. These KV key-value pairs are stored in RocksDB, and the data structure is an LSM tree.
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username: When new data is written in an LSM-Tree structure, it is first written to the in-memory Memtable. The Memtable will periodically or when it reaches a certain size, flush the data to an SSTable on the disk. When the SSTables reach a certain level, they will be compacted into a larger SSTable.
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username: However, when I execute “show index from customer” to look at a table, I see that the index_type shows BTREE. What’s going on?
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username: Initially, it was probably to be compatible with the MySQL 5.7 protocol, merely for compatibility display. The underlying actual storage is not the same.
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username: Tree structure, after watching the related video, it seems to be stored in a KV structure as well.
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username: Indexes are also encoded into KV and stored in TiKV. For encoding rules, see TiDB 数据库的计算 | PingCAP 文档中心
TiKV uses RocksDB as the key-value storage engine at the bottom layer, and the underlying data structure is LSM-tree.
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