sink(ticdc): check virtual columns in column dispatcher (#12254) #12321
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Summary of Changes
Hello @ti-chi-bot, 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 enhances the robustness of the column dispatcher by introducing explicit checks for virtual generated columns. It refines the error handling mechanism to prevent panics and provide clearer feedback when invalid column configurations are encountered, ensuring that only valid columns are processed.
Highlights
- Error Handling for Virtual Columns: The column dispatcher now explicitly checks for and prevents the use of virtual generated columns, returning an
ErrDispatcherFailederror if such columns are specified. This prevents potential panics during configuration. - Improved Column Offset Retrieval: The
OffsetsByNamesfunction incdc/model/schema_storage.gohas been updated to return anerrorinstead of a boolean, allowing for more precise error reporting when columns are not found or are virtual generated columns. - Enhanced Robustness: This change fixes a potential panic that could occur when configuring the column dispatcher with virtual columns, making the system more stable.
- Test Coverage: New unit tests have been added and existing tests updated to cover the new error handling logic for virtual and non-existent columns in the dispatcher.
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Code Review
This pull request correctly addresses a panic caused by virtual columns in the column dispatcher by adding explicit checks. The change to return an error from OffsetsByNames is a good improvement for error handling. However, I've identified a critical merge conflict in a test file that must be resolved. I also found a potential bug in OffsetsByNames where it appears to use incorrect offsets, which could lead to incorrect behavior. Additionally, there's a minor performance regression that can be easily fixed. Please see my detailed comments.
| <<<<<<< HEAD | ||
| {ID: 1, Name: timodel.NewCIStr("col2"), Offset: 1, FieldType: *types.NewFieldType(mysql.TypeLong)}, | ||
| {ID: 2, Name: timodel.NewCIStr("col1"), Offset: 0, FieldType: *types.NewFieldType(mysql.TypeLong)}, | ||
| {ID: 3, Name: timodel.NewCIStr("col3"), Offset: 2, FieldType: *types.NewFieldType(mysql.TypeLong)}, | ||
| ======= | ||
| {ID: 1, Name: pmodel.NewCIStr("col2"), Offset: 1, FieldType: *types.NewFieldType(mysql.TypeLong)}, | ||
| {ID: 2, Name: pmodel.NewCIStr("col1"), Offset: 0, FieldType: *types.NewFieldType(mysql.TypeLong)}, | ||
| {ID: 3, Name: pmodel.NewCIStr("col3"), Offset: 2, FieldType: *types.NewFieldType(mysql.TypeLong)}, | ||
| {ID: 4, Name: pmodel.NewCIStr("col4"), Offset: 3, FieldType: *types.NewFieldType(mysql.TypeLong), GeneratedExprString: "generated"}, | ||
| >>>>>>> 35ff0a22ec (sink(ticdc): check virtual columns in column dispatcher (#12254)) |
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This file contains unresolved merge conflict markers which will cause the build to fail. Please resolve the conflict. It appears the intent was to add a virtual column col4 for testing, and the alias pmodel should be timodel as used elsewhere in this file.
{ID: 1, Name: timodel.NewCIStr("col2"), Offset: 1, FieldType: *types.NewFieldType(mysql.TypeLong)},
{ID: 2, Name: timodel.NewCIStr("col1"), Offset: 0, FieldType: *types.NewFieldType(mysql.TypeLong)},
{ID: 3, Name: timodel.NewCIStr("col3"), Offset: 2, FieldType: *types.NewFieldType(mysql.TypeLong)},
{ID: 4, Name: timodel.NewCIStr("col4"), Offset: 3, FieldType: *types.NewFieldType(mysql.TypeLong), GeneratedExprString: "generated"},| if col != nil { | ||
| columnOffsets[col.Name.L] = ti.columnsOffset[col.ID] | ||
| if IsColCDCVisible(col) { | ||
| columnOffsets[col.Name.L] = ti.columnsOffset[col.ID] |
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There seems to be a bug here. ti.columnsOffset provides offsets into TableInfo.Columns, but the primary consumer of this function, ColumnsDispatcher, requires offsets into RowChangedEvent.Columns (which excludes virtual columns). Using ti.columnsOffset can lead to incorrect column access and data hashing, especially now that virtual columns are being handled. You should use ti.RowColumnsOffset instead, which is designed for this purpose and provides the correct offsets into the event's column data.
| columnOffsets[col.Name.L] = ti.columnsOffset[col.ID] | |
| columnOffsets[col.Name.L] = ti.RowColumnsOffset[col.ID] |
| columnOffsets := make(map[string]int) | ||
| virtualGeneratedColumn := make(map[string]struct{}) |
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The previous implementation pre-allocated the columnOffsets map. This change removes the pre-allocation, which is a minor performance regression. It's good practice to pre-allocate maps with a known size to avoid reallocations. You can use len(ti.Columns) - len(ti.VirtualColumnsOffset) for columnOffsets and len(ti.VirtualColumnsOffset) for virtualGeneratedColumn.
Additionally, since this function can be on a hot path for column-based dispatching, consider caching these maps in the TableInfo struct (similar to nameToColID) to avoid rebuilding them on every call. The // todo: optimize it comment suggests this is a known area for improvement.
| columnOffsets := make(map[string]int) | |
| virtualGeneratedColumn := make(map[string]struct{}) | |
| columnOffsets := make(map[string]int, len(ti.Columns)-len(ti.VirtualColumnsOffset)) | |
| virtualGeneratedColumn := make(map[string]struct{}, len(ti.VirtualColumnsOffset)) |
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This is an automated cherry-pick of #12254
What problem does this PR solve?
Issue Number: close #12241
What is changed and how it works?
Since column values don't include virtual generated columns, we also filter the virtual generated columns in the column dispatcher.
The column dispatcher now explicitly checks for and prevents the use of virtual generated columns, returning an ErrDispatcherFailed error if such columns are specified. This prevents potential panics when configuring the dispatcher.
Check List
Tests
Questions
Will it cause performance regression or break compatibility?
Do you need to update user documentation, design documentation or monitoring documentation?
Release note