Issues Related to Enabling Cold Data Archiving
What Is the Cold Data Archiving Feature?
Cold data refers to data stored in an instance that is rarely updated and infrequently accessed over a long period. Examples include historical orders, archived logs, and closed business documents. This type of data continuously occupies local disk space within the instance, yet its actual access demand is low. Cold data archiving is a data tiering storage capability provided by TDSQL Boundless. It offloads cold data from local disks to COS, enabling long-term retention of this data at a lower cost. Archived data remains accessible via normal SQL queries, but its access performance is lower than that of local hot data.
How to Enable the Cold Data Archiving Feature and Whether It Can Be Disabled Afterward
Cold data archiving is currently an allowlist feature. To use it, submit a ticket or contact Tencent Cloud technical support to apply for activation.
Attention:
Cold data archiving is an experimental feature in version V21.6.3.0. Once enabled, it cannot be disabled for now.
How Is Cold Data Archiving Billed?
Cold data archiving supports only the pay-as-you-go billing mode, with charges based on the actual storage usage for cold data offloading/archiving. No charges are incurred during the public beta.
Which Instances Support Cold Data Archiving?
Note:
The cold data archiving feature is an experimental feature in version V21.6.3.0. Currently, it can be enabled only on a subset of instances that meet the requirements.
Serverless instances are not currently supported. This feature can be enabled only on provisioned resource instances with a kernel version of V21.6.3.0 or later.
Single RG mode is not currently supported. This means that instances with a node specification below 4C (including 4C 8GB) cannot enable cold data archiving. This feature can be enabled only on instances with a node specification above 4C.
Local disk instances are not currently supported. This feature can be enabled only on enhanced SSD CBS instances.
Single-replica instances are not currently supported. This feature can be enabled only on full-featured instances that have multiple replicas or are deployed across multiple AZs.
Instances with TDE transparent data encryption enabled are not currently supported. This feature can be enabled only on instances without TDE transparent data encryption enabled.
Instances that are part of a DR relationship are not currently supported. This means that neither the primary instance nor the DR read-only instance in a DR relationship can enable the cold data archiving feature. This feature can be enabled only on regular instances.
Instances with Binlog service enabled are not currently supported. Furthermore, the cold data archiving feature and the Binlog service are mutually exclusive; only one of them can be enabled. Instances with the Read-Only Analysis Engine enabled are not currently supported. Furthermore, the Read-Only Analysis Engine and the cold data archiving feature are mutually exclusive; only one of them can be enabled. HBase compatibility mode is not currently supported. Only MySQL compatibility mode is supported.
This feature can be enabled only on instances that are in the Running state.
What Scenarios Are Not Supported by Cold Data Archiving?
Note:
The cold data archiving feature is an experimental feature in version V21.6.3.0. Currently, it has the following usage restrictions. This feature will be gradually improved. Please stay tuned for updates.
Cold data warming (data recall) is not currently supported. This means that tables or partitions that have been archived to cold storage cannot be migrated back to the original engine.
Automatic identification of cold data and automatic archiving to cold storage are not currently supported.
Backup and recovery are not currently supported. After the COS hot/cold tiering feature is enabled, instance backup and recovery are not supported, and creating disaster recovery instances is also not supported.
Bulk loading data via Bulk Load is not currently supported. Importing data using the LOAD DATA INFILE method is also not supported. The table creation syntax CREATE TABLE ... AS SELECT ... FROM ... is not currently supported.
Fast Online DDL on cold tables is not currently supported. Only a limited subset of Online DDL operations is supported (specifically, those that go through the thomas write path). Enabling the KV separation feature is not currently supported. If KV separation is already enabled locally, data cannot be archived to COS. Enabling the large transaction feature is not currently supported.
Enabling the TDE transparent encryption feature is not currently supported.
Changing the AZ of an instance is not currently supported. Other unsupported operations include adjusting the number of replicas, migration with specification change, and horizontal scale-in (reducing the number of nodes or disk space).
Scheduling tasks such as splitting, merging, or migrating cold RGs are not currently supported.
How to Enable Cold Data Archiving in a Lower Edition
You can upgrade TDSQL Boundless to a compliant version. To do this, you can contact Tencent Cloud Technical Support to upgrade the instance version.
Issues Related to Using Cold Data Archiving
How to Convert Data of a Table/Partition to Cold Data
Note:
Currently, only manually specifying a table or table partition for cold archiving is supported. Automatic identification and archiving of cold data is not yet supported.
After you enable the cold data archiving feature, you can manually archive data to cold storage using SQL statements:
ALTER TABLE <table_name> STORAGE_TIER = OBJECT_STORAGE;
ALTER TABLE <table_name>
MODIFY PARTITION (<partition_name>) STORAGE_TIER = OBJECT_STORAGE;
Can Data Still Be Written to Archived Tables or Partitions?
Archived tables or partitions still support normal read and write operations, but do not support batch loading methods such as Bulk Load or LOAD DATA INFILE. How to Query Archived Cold Data
After performing cold data archiving on regular tables or partition tables, you can query the archived cold data using the following methods:
Regular tables: After cold data archiving is performed, the method for querying cold data is the same as that for querying hot data, and no modification to the access method is required.
Partition tables: After cold data archiving is performed on some partitions, you can query the cold data in two ways:
Method 1: Direct query. The method for querying cold data is the same as that for querying hot data, and no modification to the access method is required.
ALTER TABLE t1
MODIFY PARTITION (p1) STORAGE_TIER = OBJECT_STORAGE;
SELECT * FROM t1 WHERE <condition>
Method 2: Query by specifying the cold partitions.
ALTER TABLE t1
MODIFY PARTITION (p1) STORAGE_TIER = OBJECT_STORAGE;
SELECT * FROM t1 partition (p1) WHERE <condition>
How to Determine Whether a Table or Partition Has Been Successfully Archived to Cold Storage
After archiving is completed, you can use the following two methods to check whether the table or partition has been successfully archived:
Execute the SHOW CREATE TABLE table_name; command to view the table schema information, thereby confirming whether the table or partition has been successfully archived.
Regular tables: If the returned information displays STORAGE_TIER = OBJECT_STORAGE, it indicates that the current data has been successfully archived.
Partition tables: If a partition in a partition table shows STORAGE_TIER = OBJECT_STORAGE, it indicates that the current data has been successfully archived.
To check whether the archiving is successful on the console: Log in to the TDSQL Boundless console, go to the instance details, and on the Data Archiving tab, in the Data Archiving List, check whether the corresponding table name exists. If it exists, it indicates that the current data has been archived to COS. Reliability of Archived Tables
The storage for archived tables is placed on a multi-AZ COS, providing cross-AZ disaster recovery within the region and tolerating single-AZ failures.
Can Archived Tables Be Converted Back to Hot Data?
Not supported. The capability to warm cold data is not currently provided, meaning the following SQL is not supported:
ALTER TABLE <table_name> STORAGE_TIER = RocksDB;
How to Delete Archived Cold Data
You can delete/purge archived tables, or delete archived cold data by deleting/purging archived tables/partitions.
TRUNCATE TABLE <table_name>;
ALTER TABLE <table_name> TRUNCATE PARTITION <partition_name>;
DROP TABLE <table_name>;
ALTER TABLE <table_name> DROP PARTITION <partition_name>;
Issues Related to Cold Data Archiving Space Usage
How to View the Size of Archived Cold Data
You can view the size of archived cold data on the console, or directly query the corresponding cold data table on the instance. For detailed operations, see View Cold Data Archiving Information. Does Cold Data Occupy Disk Space on Instance Peer Nodes?
No. Cold data is stored on COS, which does not occupy the disk space of peer nodes in the instance, thereby freeing up the disk resources of peer nodes for hot data.
Should the Original Table Be Manually Deleted After Cold Data Archiving to Save Storage Space?
After cold data archiving, TDSQL Boundless only stores the metadata information of the table. The actual data information is stored on COS, which does not affect your storage space, so manual deletion is not required.
Does the Data Volume of Archived Cold Data Increase or Decrease Compared to the Original Table?
The data format of archived cold data is not changed, meaning the storage capacity occupied by the original table remains almost unchanged.
Does Data Capacity Change After TDSQL Boundless Is Archived to COS?
After cold data is archived to COS, the local high-performance storage will asynchronously delete the cold-archived data with a delay. Consequently, the data occupancy of local storage (local disks/cloud disks) decreases, while the usage of COS increases correspondingly.
Why Are Archived Cold Data and Files Not Visible in COS Under the Root Account?
The cold data of TDSQL Boundless is stored in the system-default COS, not in the customer's COS, so customers cannot view it. Currently, you can only view archived cold data and files on the console. Directly viewing COS files is not supported.