In Protocol Buffers, field names are not important, whereas the field names are important in all programming language. In the Protocol Buffers the Tag tag name.
- Smallest tag : 1
- Largest tag : 2^29 - 1 or 536,870,911
The tags 19000 to 19999 are reserved by the Google. Hence you cannot use this tags in proto file.
The tag numbered from 1 to 15 use 1 byte in space, so use them for more frequently populated fields to minimise the space. And the tag numbered from 16 to 2047 use 2 bytes.
Each field if value is not set it has asscoiated default value.
| Field Type | Default Value |
|---|---|
| bool | false |
| number | 0 |
| string | empty string |
| list | empty list |
| enum | first value |
| repeated | empty list |
There is no concept of required field or optional field in protocol buffer