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70 lines
2.1 KiB
Markdown
70 lines
2.1 KiB
Markdown
# Hybrid Timestamp in Milvus
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In chapter [Milvus TimeSync Mechanism](./milvus_timesync_en.md), we have already known why we need TSO in Milvus. Milvus
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uses the [TiKV's](https://github.com/tikv/tikv) implementation into TSO. So if you are interested in how TSO is
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implemented, you can look into the official documentation of TiKV.
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This chapter will only introduce two points:
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1. the organization of hybrid TSO in Milvus;
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2. how should we parse the hybrid TSO;
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## The Organization of TSO
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The type of TSO is `uint64`. As shown in the figure below, TSO was organized by two parts:
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1. physical part;
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2. logical part;
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The front 46 bits is of physical part, and the last 18 bits is of logical part.
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Note, physical part is the UTC time in Milliseconds.
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For some users such as DBAs, they would want to sort the operations and list them in UTC time order.
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Actually, we can use the TSO order to sort the `Insert` operations or `Delete` operations.
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So the question becomes how we get the UTC time from TSO.
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As we have described above, the physical part consists of the front 46 bits of TSO.
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So given a TSO which is returned by `Insert` or `Delete`, we can directly shift the left 18 bits to get the UTC time.
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For example in Golang:
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```go
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const (
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logicalBits = 18
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logicalBitsMask = (1 << logicalBits) - 1
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)
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// ParseTS parses the ts to (physical,logical).
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func ParseTS(ts uint64) (time.Time, uint64) {
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logical := ts & logicalBitsMask
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physical := ts >> logicalBits
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physicalTime := time.Unix(int64(physical/1000), int64(physical)%1000*time.Millisecond.Nanoseconds())
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return physicalTime, logical
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}
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```
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In Python:
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```python
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>>> import datetime
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>>> LOGICAL_BITS = 18
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>>> LOGICAL_BITS_MASK = (1 << LOGICAL_BITS) - 1
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>>> def parse_ts(ts):
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... logical = ts & LOGICAL_BITS_MASK
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... physical = ts >> LOGICAL_BITS
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... return physical, logical
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...
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>>> ts = 429164525386203142
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>>> utc_ts_in_milliseconds, _ = parse_ts(ts)
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>>> d = datetime.datetime.fromtimestamp(utc_ts_in_milliseconds / 1000.0)
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>>> d.strftime('%Y-%m-%d %H:%M:%S')
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'2021-11-17 15:05:41'
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>>>
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```
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