Unobtrusive copies of actively used compressed indices

摘要

Methods, devices and systems to make compressed backup copies of in-use compressed database indices are described. In general, an “oldest” time at which index pages in working memory had been updated is identified. Compressed index pages may be directly copied without the need to bring them into working memory or uncompressing them. The identified “oldest” time is then associated with the compressed backup copy. In some embodiments, an entire compressed backup copy may be associated with a single point in time (e.g., the identified “oldest” time). In other embodiments, a compressed backup copy may be associated with multiple points in time (e.g., one time for each portion of the compressed index that is being backed-up). Compressed indices copied in accordance with the invention may be used during restore operations to reconstruct database indices using the identified “oldest” time and database log files.

主权项

1. A general purpose computer comprising:
at least one processor; and at least one storage device tangibly embodying program instructions that, when executed by the at least one processor, are configured to cause the general purpose computer to at least:
for each of a plurality of pages associated with a target index:
write the page to external storage; andstore a time of the writing the page to the external storage as an externalization time of the page; andafter performing the writing and the storing:
determine which pages in a buffer memory are associated with the target index;identify an externalization point of the target index, the externalization point corresponding to an oldest change to a page associated with the target index that has not been written to the external storage;for each of the pages associated with the target index that is stored in the buffer memory, if the externalization point of the target index is earlier than the externalization time of the page, write the page from the buffer memory to an output file; andfor each of the pages associated with the target index that is not stored in the buffer memory, and each of the pages associated with the target index and stored in the buffer memory for which the externalization point of the target index is later than the externalization time of the page, copy the page from the external storage to the output file without bringing the page into the buffer memory.