SELECTIVE DATA COMPRESSION FOR IN-MEMORY DATABASES

摘要

Techniques are provided for maintaining data persistently in one format, but making that data available to a database server in more than one format. For example, one of the formats in which the data is made available for query processing is based on the on-disk format, while another of the formats in which the data is made available for query processing is independent of the on-disk format. Data that is in the format that is independent of the disk format may be maintained exclusively in volatile memory to reduce the overhead associated with keeping the data in sync with the on-disk format copies of the data. Selection of data to be maintained in the volatile memory may be based on various factors. Once selected the data may also be compressed to save space in the volatile memory. The compression level may depend on one or more factors that are evaluated for the selected data. The factors for the selection and compression level of data may be periodically evaluated, and based on the evaluation, the selected data may be removed from the volatile memory or its compression level changed accordingly.

主权项

1. A method comprising:
maintaining, by a database server, a database on persistent storage; wherein the database includes:
a first data portion, that has been designated as eligible for mirroring within volatile memory; anda second data portion that has been also designated as eligible for mirroring within the volatile memory; storing first eligibility data that corresponds to the first data portion, wherein the first eligibility data reflects an estimated benefit of having the first data portion mirrored in the volatile memory; storing second eligibility data that corresponds to the second data portion, wherein the second eligibility data reflects an estimated benefit of having the second data portion mirrored in the volatile memory; wherein the first eligibility data and the second eligibility data are determined by the database server based on one or more factors; based on the first eligibility data, automatically determining that the first data portion should not be loaded into the volatile memory; based on the second eligibility data, automatically determining that the second data portion should be loaded into the volatile memory; and in response to a load event that causes data portions to be mirrored within the volatile memory, loading, into the volatile memory, data from the second data portion without loading into volatile memory any data from the first data portion.