Asynchronous shifting windows caching for forward and backward video streaming

A computer-implemented method of operating a cache memory for forward playback and backward playback of video data to a host application from a video file in a storage array, the method comprising:

• fetching a first segment of data from the video file in the storage array and storing the first segment of data in the cache memory;
• fetching a second segment of data from the video file in the storage array and storing the second segment of data in the cache memory, the second segment of data being contiguous with and following the first segment of data in the video file;
• fetching a third segment of data from the video file in the storage array and storing the third segment of data in the cache memory, the third segment of data being contiguous with and preceding the first segment of data in the video file;
• and
• after the fetching of the first, second, and third segments of data from the video file in the storage array and the storing of the first, second, and third segments of data in the cache memory, receiving from the host application a request for data from the video file beginning at a specified offset in the video file, and responding to the request for data by searching the cache memory for data from the video file at the specified offset in the video file and finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, and in response to finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, returning data from the third segment of data in the cache memory to the host application and fetching a fourth segment of data from the video file in the storage array and storing the fourth segment of data from the video file in the cache memory, the fourth segment of data being contiguous with and preceding the third segment of data in the video file;
• wherein the fetching of the first segment of data from the video file in the storage array is performed during a first fetching process in response to an initial read request from the host application for data from the video file, and returns data requested by the initial read request to the host application after the first segment of data in the cache memory has been loaded into the cache memory;
• and after the first fetching process, further in response to the initial read request from the host computer for data from the video file, performing the fetching of the second segment of data from the video file in the storage array and storing the second segment of data in the cache memory during a second fetching process that is asynchronous with the return of data requested by the initial read request to the host application, and thereafter, further in response to the initial read request from the host application for data from the video file in the storage array, performing the fetching of the third segment of data from the video file in the storage array and storing the third segment of data in the cache memory during a third fetching process that is asynchronous with the return of data requested by the initial read request to the host application;
• and
• wherein further computing a distance between an offset specified by the first read request and an offset specified by the second read request and comparing the distance to a threshold and finding that the comparison indicates that the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file.

In a data processing system including a host computer and a storage array coupled to the host computer for servicing storage access requests from the host computer, the host computer having a cache memory and being programmed with a video application and a video file manager, a computer-implemented method of operating the host computer for forward playback and backward playback of video data to the video application from a video file in the storage array, the method comprising:

• the video file manager fetching a first segment of data from the video file in the storage array and storing the first segment of data in the cache memory;
• the video file manager fetching a second segment of data from the video file in the storage array and storing the second segment of data in the cache memory, the second segment of data being contiguous with and following the first segment of data in the video file;
• the video file manager fetching a third segment of data from the video file in the storage array and storing the third segment of data in the cache memory, the third segment of data being contiguous with and preceding the first segment of data in the video file;
• after the fetching of the first, second, and third segments of data from the video file in the storage array and the storing of the first, second, and third segments of data in the cache memory, the video file manager receiving, from the video application, a request for data from the video file beginning at a specified offset in the video file, and the video file manager responding to the request for data by searching the cache memory for data from the video file at the specified offset in the video file and finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, and in response to finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, returning data from the third segment of data in the cache memory to the video application and fetching a fourth segment of data from the video file in the storage array and storing the fourth segment of data from the video file in the cache memory, the fourth segment of data being contiguous with and preceding the third segment of data in the video file;
• wherein the video file manager performs a search of cache state information in response to an initial sequence of first and second read requests from the host application for reading data from the video file, and performing the fetching of the first, second, and third segments of data from the video file in the storage array in response to the search of the cache state information finding that the cache state information indicates that:
• (a) buffers have already been allocated in the cache memory for buffering the first, second, and third segments of the data from the video file, and (b) the buffers do not include the data requested by the second read request, and (c) the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file;
• and
• wherein the video file manager determines that the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file upon computing a distance between an offset specified by the first read request and an offset specified by the second read request and comparing the distance to a threshold and finding that the comparison indicates that the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file.

A data processing system comprising a host computer and a storage array coupled to the host computer for servicing storage access requests from the host computer, the host computer having a cache memory and being programmed with a video application and a video file manager, the video file manager being executable by the host computer for:

• fetching a first segment of data from the video file in the storage array and storing the first segment of data in the cache memory;
• fetching a second segment of data from the video file in the storage array and storing the second segment of data in the cache memory, the second segment of data being contiguous with and following the first segment of data in the video file;
• fetching a third segment of data from the video file in the storage array and storing the third segment of data in the cache memory, the third segment of data being contiguous with and preceding the first segment of data in the video file;
• after the fetching of the first, second, and third segments of data from the video file in the storage array and the storing of the first, second, and third segments of data in the cache memory, for receiving, from the video application, a request for data from the video file beginning at a specified offset in the video file, and for responding to the request for data by searching the cache memory for data from the video file at the specified offset in the video file and finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, and in response to finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, for returning data from the third segment of data in the cache memory to the video application and fetching a fourth segment of data from the video file in the storage array and storing the fourth segment of data from the video file in the cache memory, the fourth segment of data being contiguous with and preceding the third segment of data in the video file;
• wherein the video file manager is further executable by the host computer for performing a search of cache state information in response to an initial sequence of first and second read requests from the video application for reading data from the video file, and performing the fetching of the first, second, and third segments of data from the video file in the storage array in response to the search of the cache state information finding that the cache state information indicates that:
• (a) buffers have already been allocated in the cache memory for buffering the first, second, and third segments of the data from the video file, and (b) the buffers do not include the data requested by the second read request, and (c) the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file;
• and
• wherein the video file manager is further executable by the host computer for determining that the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file upon computing a distance between an offset specified by the first read request and an offset specified by the second read request and comparing the distance to a threshold and finding that the comparison indicates that the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file.

A data processing system comprising a host computer and a storage array coupled to the host computer for servicing storage access requests from the host computer, the host computer having a cache memory and being programmed with a video application and a video file manager, the video file manager being executable by the host computer for:

• fetching a first segment of data from the video file in the storage array and storing the first segment of data in the cache memory;
• fetching a second segment of data from the video file in the storage array and storing the second segment of data in the cache memory, the second segment of data being contiguous with and following the first segment of data in the video file;
• fetching a third segment of data from the video file in the storage array and storing the third segment of data in the cache memory, the third segment of data being contiguous with and preceding the first segment of data in the video file;
• after the fetching of the first, second, and third segments of data from the video file in the storage array and the storing of the first, second, and third segments of data in the cache memory, for receiving, from the video application, a request for data from the video file beginning at a specified offset in the video file, and for responding to the request for data by searching the cache memory for data from the video file at the specified offset in the video file and finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, and in response to finding that the data from the video file at the specified offset is in the third segment of data in the cache memory, for returning data from the third segment of data in the cache memory to the video application and fetching a fourth segment of data from the video file in the storage array and storing the fourth segment of data from the video file in the cache memory, the fourth segment of data being contiguous with and preceding the third segment of data in the video file;
• wherein the video file manager is further executable by the host computer for performing the fetching of the first segment of data from the video file in the storage array during a first fetching process in response to an initial read request from the video application for data from the video file, and for returning data requested by the initial read request to the video application after the first segment of data in the cache memory has been loaded into the cache memory;
• and after the first fetching process, further in response to the initial read request from the video application for data from the video file, for performing the fetching of the second segment of data from the video file in the storage array and storing the second segment of data in the cache memory during a second fetching process that is asynchronous with the return of data requested by the initial read request to the video application, and thereafter, further in response to the initial read request from the video application for data from the video file in the storage array, for performing the fetching of the third segment of data from the video file in the storage array and storing the third segment of data in the cache memory during a third fetching process that is asynchronous with the return of data requested by the initial read request to the video application;
• and
• wherein the video file manager is further executable by the host computer for determining that the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file upon computing a distance between an offset specified by the first read request and an offset specified by the second read request and comparing the distance to a threshold and finding that the comparison indicates that the initial sequence of the first and second read requests is likely to be the beginning of a sequential access of the video file.