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TDSQL Boundless

DocumentaçãoTDSQL BoundlessKernel FeaturesPerformance FeaturesTDStore Key-Value SeparationUsage Constraints and Considerations

Usage Constraints and Considerations

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Última atualização: 2026-05-26 11:28:35

Permissions and Validity

All tdstore_user_cf_*blob* parameters require SUPER privileges to be modified.
Most parameters support online dynamic modification, which takes effect immediately for new writes.
Exception: The tdstore_enable_blob_cache parameter (shared Blob Cache switch) is READ_ONLY. It can only be specified in the startup configuration and takes effect after a restart.

Data Format Version Downgrade Not Supported

When tdstore_user_cf_enable_blob_files = ON is enabled for the first time, if tdstore_rocksdb_data_format_version is UNKNOWN, the system automatically upgrades to ROCKSDB_DATA_FORMAT_VERSION_1 and returns a Warning to the client.
Once an instance is upgraded to v1, you cannot downgrade to a previous version. This means that after Key-Value separation is enabled, rolling back to an older TDSQL instance that does not support BlobDB will be restricted.
Recommendation: Include "whether to enable KV separation" as a decision item during the upgrade assessment.

Switch Granularity Restrictions

The granularity for enabling or disabling KV separation is at the Column Family level. It does not support table-level / Region-level switches.
After KV separation is enabled for the user CF, large values in all tables within the user CF are separated.
To apply the change only to specific large tables, you can set a higher threshold for tdstore_user_cf_min_blob_size to prevent small-value tables from being affected.

Residual Data After Disabling is Performed

After enable_blob_files is disabled, existing Blob files are not deleted immediately. They must wait for subsequent Compaction to merge them naturally.
To quickly reclaim disk space, a DBA can manually trigger Compaction.

Relationship with Other Features

Feature
Compatibility
Primary/Secondary Synchronization / Raft Replication
Fully compatible, with Blob files synchronized along with snapshots and logs.
Region Split / Merge
Fully compatible
Backup / Restore
Fully compatible, with Blob files packaged along with backups.
Secondary Index Operations
Fully compatible (index columns typically do not trigger separation).
Columnar Storage (Columnar)
Compatible, with the columnar metadata CF having an independent switch that does not affect the user CF.
Tiered Storage (Tiered Store)
Compatible, with the cache CF having an independent switch.
Anterior: MetricsPróximo: Upgrade and Compatibility

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