feat: [TS-6665] Support 65535 cols.

[Simon9997]

Description

Please briefly describe the code changes in this pull request.

Jira: https://jira.taosdata.com:18080/browse/TD-

Checklist

Please check the items in the checklist if applicable.

• Is the user manual updated?
• Are the test cases passed and automated?
• Is there no significant decrease in test coverage?

[gemini-code-assist]

Summary of Changes

Hello @Simon9997, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a significant enhancement by increasing the maximum number of columns supported within the database system. This change directly addresses the need for greater flexibility in schema design, allowing for tables with up to 65535 columns, thereby accommodating more complex and extensive datasets.

Highlights

• Maximum Columns: The TSDB_MAX_COLUMNS macro, which defines the maximum number of columns supported in the database, has been updated from 4096 to 65535. This change directly implements the feature to support a higher column count.

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[gemini-code-assist]

Code Review

This pull request increases the maximum number of columns to 65535. While the change is small, it has critical side effects. The data type for column IDs (col_id_t) is an int16_t, which will overflow with more than 32,767 columns, leading to severe bugs. This must be changed to int32_t throughout the codebase. Additionally, this change significantly increases the size of several memory buffers (e.g., up to 16MB), which could cause performance issues or out-of-memory errors. These impacts need to be carefully evaluated, and the empty pull request description should be updated to reflect the scope and consequences of this feature.

[gemini-code-assist]

Increasing TSDB_MAX_COLUMNS to 65535 is not safe due to a data type overflow. The type col_id_t, used for column IDs, is defined as int16_t in include/common/ttypes.h, which can only hold values up to 32,767. Using column IDs larger than this will cause an integer overflow, leading to unpredictable behavior and likely data corruption.

Given that special negative values like TSDB_TBNAME_COLUMN_INDEX (-1) are used for column identifiers, col_id_t and all related fields (e.g., SColumn.colId) must be changed to a larger signed type, such as int32_t, to safely accommodate up to 65,535 columns. This is a critical change that needs to be applied consistently across the entire codebase wherever column IDs are handled.

[gemini-code-assist]

This change significantly increases the memory footprint of several components. Buffers sized with TSDB_MAX_COLUMNS will become much larger. For example:

• TSDB_MAX_SAVED_SQL_LEN (line 302) will grow from ~256 KB to ~4 MB.
• TSDB_SHOW_SCHEMA_JSON_LEN (line 341) will grow from 1 MB to ~16 MB.

These large allocations, especially if on the stack, could lead to stack overflows or out-of-memory errors in environments with limited resources. Please confirm that this increased memory usage is acceptable and has been tested. The impact of these changes should be documented in the pull request description.