refactor: create JsonValue for json value

[MichaelScofield]

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Refer to a related PR or issue link (optional)

What's changed and what's your intention?

Make json value represented as struct JsonValue, instead of Value. New json value has its fields sorted, which is more convenient for further use. And lesser verbose codes when dealing with different json variants.

related proto change: GreptimeTeam/greptime-proto#289

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[Copilot]

Pull Request Overview

This PR refactors JSON value representation by introducing a dedicated JsonValue struct instead of using the generic Value type. The new implementation uses BTreeMap for JSON objects to maintain sorted field ordering, simplifying code when working with different JSON variants.

• Introduces new JsonValue, JsonValueRef, JsonVariant, and JsonVariantRef types with sorted field support
• Updates JSON encoding/decoding logic to use the new types throughout the codebase
• Enforces homogeneous type requirements for JSON array items (all items must have the same type)

Reviewed Changes

Copilot reviewed 13 out of 14 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/datatypes/src/json/value.rs	New file defining JsonValue and related types with sorted JSON object fields using BTreeMap
src/datatypes/src/value.rs	Updated Value enum to use Box<JsonValue> instead of Box<Value> for JSON variant
src/datatypes/src/json.rs	Refactored JSON encoding/decoding to use JsonValue types and enforce array type homogeneity
src/datatypes/src/types/json_type.rs	Added helper methods and extracted plain_json_struct_type function
src/datatypes/src/vectors/json/builder.rs	Updated JSON vector builder to work with new JsonValueRef type
src/api/src/helper.rs	Added encode_json_value and decode_json_value functions for protobuf conversion
src/frontend/src/limiter.rs	Updated size calculation logic for new JSON value structure
src/partition/src/collider.rs	Added clippy allow annotation for mutable key type usage
Cargo.toml / Cargo.lock	Updated greptime-proto dependency to support new JSON value representation

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[sunng87]

Just want to double-check with this JsonValue, are we still using Arrow's Struct for json object internally? Because we need that for flattening nested data in parquet, which is of critical importance to ensure a columnar format for json

[MichaelScofield]

Just want to double-check with this JsonValue, are we still using Arrow's Struct for json object internally? Because we need that for flattening nested data in parquet, which is of critical importance to ensure a columnar format for json

@sunng87 Physically the JsonValue is still stored as Arrow Struct, see https://github.com/GreptimeTeam/greptimedb/pull/7214/files#diff-fe8d389bf14fcacc04453c6b51e9ee8d21af580ba700fe944914c252047b43f8R44 and https://github.com/GreptimeTeam/greptimedb/pull/7214/files#diff-02bc4a0d88d5e644788241668f9d295cd9be7a9c37c179bf45a136a93932eee5R611

[MichaelScofield]

@sunng87 @copilot PTAL

[Copilot]

@MichaelScofield I've opened a new pull request, #7217, to work on those changes. Once the pull request is ready, I'll request review from you.

[MichaelScofield]

@copilot review

[Copilot]

@MichaelScofield I've opened a new pull request, #7218, to work on those changes. Once the pull request is ready, I'll request review from you.