Add docs for Timeseries (#324)
diff --git a/community/data-structure-on-rocksdb.md b/community/data-structure-on-rocksdb.md
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+++ b/community/data-structure-on-rocksdb.md
@@ -453,3 +453,88 @@
| (8byte) double |
+----------------+
```
+
+## TimeSeries
+
+RedisTimeSeries is a Redis module that enables a full-featured time-series database within Redis. To bring this powerful capability to Kvrocks, we've implemented a compatible TimeSeries data structure, leveraging RocksDB for efficient storage and retrieval.
+
+#### TimeSeries metadata
+
+The metadata stores the overall configuration for a single time series, such as retention, duplicate policy and chunk settings.
+
+```text
+ +----------+----------+-----------+------------------+----------------+-----------+-----------+----------------+----------------+-----------+
+key => | flags | expire | version | size(chunkCount) | retentionTime | chunkSize | chunkType | duplicatePolicy| sourceKey_size | sourceKey |
+ | (1byte) | (Ebyte) | (8byte) | (Sbyte) | (8byte) | (8byte) | (1byte) | (1byte) | (4byte) | (Xbyte) |
+ +----------+----------+-----------+------------------+----------------+-----------+-----------+----------------+----------------+-----------+
+```
+- `retentionTime`: Maximum age (in milliseconds) for samples compared to the latest timestamp. A value of `0` disables retention.
+- `chunkSize`: The preferred number of samples per data chunk.
+- `chunkType`: The storage format of the chunk (compressed or uncompressed).
+- `duplicatePolicy`: An enum represents the policy to handle samples with duplicate timestamps (e.g., BLOCK, FIRST, LAST).
+- `sourceKey`: If this series is a downstream target for compaction, this field stores the key of the source series.
+
+#### TimeSeries sub keys-values
+
+Internally, TimeSeries data structure uses several types of sub-keys to store its components: **time chunks**, **labels**, and **downstream rule metadata**. A **key type** enum is used as a prefix in the key to differentiate between them.
+
+| key type | enum value |
+| ------------ | ---------- |
+| `CHUNK` | 0 |
+| `LABEL` | 1 |
+| `DOWNSTREAM` | 2 |
+
+##### CHUNK sub keys
+The actual time series data is stored in sequential blocks called **chunks**. Each chunk is identified by a `chunk_id`, which corresponds to the timestamp of the first sample within that chunk.
+
+```text
+ +--------+------------+----------+------------+----------+ +------------+----------+
+key|version|CHUNK|chunk_id => | count | timestamp1 | value1 | timestamp2 | value2 |...| timestampN | valueN |
+ |(8byte) | (8byte) | (8byte) | (8byte) | (8byte) |...| (8byte) | (8byte) |
+ +--------+------------+----------+------------+----------+ +------------+----------+
+```
+
+##### LABEL sub keys
+These sub keys store label key-value pairs associated with the time series.
+
+```text
+ +----------------+
+key|version|LABEL|label_key1 => | label_value1 |
+ | (Xbyte) |
+ +----------------+
+ +----------------+
+key|version|LABEL|label_key2 => | label_value2 |
+ | (Xbyte) |
+ +----------------+
+...
+```
+
+##### DOWNSTREAM sub keys
+Kvrocks supports RedisTimeSeries's compaction rules, which automatically aggregate data from a source series into a destination (or downstream) series. This sub-key stores the configuration for each compaction rule applied to the source series.
+
+```text
+ +-------------+----------------+-------------+---------------------+------------+
+key|version|DOWNSTREAM|downstream_key => | aggregator |bucket_duration | alignment | latest_bucket_index | auxinfo |
+ | (1byte) | (8byte) | (8byte) | (8byte) | (XByte) |
+ +-------------+----------------+-------------+---------------------+------------+
+```
+- `aggregator`, `bucket_duration`, `alignment` are the parameters defined by the [compaction rule](https://redis.io/docs/latest/commands/ts.createrule/).
+- `latest_bucket_index`: Tracks the index of the latest bucket to optimize ongoing aggregations.
+- `auxinfo`: Auxiliary data to speed up aggregations without re-scanning the entire bucket. Upon appending samples, it is [updated whenever a new chunk is created](https://github.com/apache/kvrocks/blob/b5b419995c8327bd07a6d63090da367d98f59b72/src/types/redis_timeseries.cc#L322) in the source series.
+
+#### label-based reverse index
+
+To enable fast, label-based queries, a reverse index is maintained. This index is critical for efficiently locating all time series that match a given set of label filters. It is stored in a dedicated `Index` Column Family.
+
+```text
++-------------+-------------+------------+--------------+---------+
+| namespace | index type | label_key | label_value | key | => null
+| (1+Xbyte) | (1byte) | (4+Ybyte) | (4+Zbyte) | (Kbyte) |
++-------------+-------------+------------+--------------+---------+
+
+```
+`index type` is an enum that distinguishes between different types of indexes. For TimeSeries, it currently includes the following value:
+
+| index type | enum value |
+| ------------ | ---------- |
+| `TS_LABEL` | 0 |
