In a PolarDB-X Enterprise Edition instance, you can use the cold data archiving feature to archive infrequently accessed and rarely updated data to Object Storage Service (OSS). This can significantly reduce data storage costs. This topic describes the cold data archiving feature.
Working mechanism
By default, the data of a PolarDB-X Enterprise Edition instance is stored on on-premises disks. The cold data archiving feature allows you to classify the data into hot (frequently accessed) and cold (infrequently accessed) categories based on its age. The feature separates cold data from the table and archives it into archived tables in Object Storage Service (OSS).
Cold data is stored in OSS in the column store format, and hot data is stored on on-premises disks in the row store format.
After cold data archiving is performed, the table is split into a source table in which hot data is stored and an archived table in which cold data is stored.
The archived tables in OSS deliver poor query performance. Therefore, an archived table is named differently from the source table to ensure the service level agreement (SLA) of data queries.
Similar to source tables, archived tables also support various features, including highly efficient point queries by primary key or index, complex analytic queries, high availability, compatibility with MySQL, and data flashback to an earlier point of time. You can access archived tables in the same manner that you access MySQL tables. You can also use open source big data products to access archived data in OSS.
Billing
The storage used by cold data is separately billed based on the pay-as-you-go billing method. The following table describes the billing method.
Billing method | Storage price |
Pay-as-you-go | CNY 0.000167 per GB-hour |
Limits
This feature is available only for TTL tables in databases in AUTO mode.
Specific DDL operations for column modifications are supported only on instances of PolarDB-X 5.4.17-16835173 and later. DDL operations cannot be performed on archived tables in instances of PolarDB-X 5.4.14 to 5.4.16.
After you associate an archived table with a TTL table, specific DDL operations on the original TTL table are restricted. You can execute the
UNARCHIVE TABLE {source_table_name}statement to disassociate the archived table from the TTL table. After you disassociate the archived table from the TTL table, you must associate a new archived table with the TTL table.