System for updating modified pages of data object represented in concatenated multiple virtual address spaces

• US 5,594,881 A
• Filed: 05/17/1995
• Issued: 01/14/1997
• Est. Priority Date: 11/12/1991
• Status: Expired due to Term

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Fecteau, Jean G., Kollar, Lubor, Kligerman, Eugene
• Primary Examiner(s): KIM, KENNETH S
• Application Number:
  US08/443,397
• Time in Patent Office: 608 Days
• Field of Search: 395/416, 395/418, 395/419, 395/468, 395/488, 395/600, 395/700, 395/413
• US Class Current: 711/209
• CPC Class Codes: G06F 12/0292 using tables or multilevel address translation means G06F12/023 takes precedence; address translation in virtual memory systems G06F12/10
• CPC Class Codes: G06F 12/0882 Page mode
• CPC Class Codes: G06F 12/109 for multiple virtual address spaces, e.g. segmentation G06F12/1036 takes precedence
• CPC Class Codes: Y10S 707/99931 Database or file accessing
• CPC Class Codes: Y10S 707/99945 Object-oriented database structure processing
• CPC Class Codes: Y10S 707/99953 Recoverability
• CPC Class Codes: Y10S 707/99956 File allocation

Abstract

Method and means are provided for simulating a contiguous data space within a computer memory, and for placing and accessing data objects of various sizes within the simulated contiguous data space. Multiple, sub-data spaces are concatenated in such a way that each page and each sub-data space in the contiguous data space are uniquely identified. Data objects are placed in the contiguous data space and at the first reference to a page of the data object, only the segment containing the referenced page in the contiguous data space is mapped to the database storage disk. Once a data space page is mapped, the operating system can read the page into memory without requesting a disk operation from the database manager. On modifying a page, if the database disk page location is changed, the contiguous data space page is remapped without changing the page address in the data space. Also, modified data pages are rewritten to the database storage disk in an ongoing manner set by the user, instead of at intervals set by the operating system.

Claims

1. A method for modifying a page of a data object contained in a database and stored in one or more database storage disks, wherein the database comprises one or more database data objects, wherein the database is accessed via a contiguous data space representation, the contiguous data space being represented by a plurality of concatenated sub-data spaces, wherein each sub-data space is a virtual data space of a maximum size that is addressable by a computer operating system, each sub-data space comprising a plurality of data segments, each data segment comprising a plurality of pages, wherein the pages in the contiguous data space representation are contiguous, each page comprising a known number of addressable storage locations, wherein the contiguous data space, the sub-data spaces, the data segments, and the pages are addressable by a database management system, wherein the address of a page to be modified has been determined to be placed in a sub-data space, the method comprising the steps of:

(1) mapping a data segment of the data object from a database storage disk to a data segment of the sub-data space, wherein said data segment from said database storage disk contains the page to be modified;

(2) creating a modified section bit map for the sub-data space, wherein said modified section bit map comprises a plurality of bits, each bit representing a group of pages of the sub-data space and indicating whether one or more pages in said group has been modified;

(3) indicating that the page to be modified has been modified, thereby creating a modified page, by setting a bit in said modified section bit map to a predetermined value, wherein said bit represents a group containing said modified page;

(4) generating a modified section count representing a number of bits in said modified section bit map that are equal to said predetermined value; and

(5) issuing an asynchronous request to save one or more groups of pages of the sub-data space corresponding to bits in said modified section bit map that are equal to said predetermined value when said modified section count corresponds to a modified section threshold.

3. The method of claim 1, further comprising the step of:

(6) issuing a synchronous request to save one or more groups of pages of each said sub-data space corresponding to bits in each said modified section bit map that are equal to said predetermined value when the database management system determines that a checkpoint is required, wherein the database management system waits for all outstanding asynchronous requests to complete.

2. A method for modifying a page of a data object contained in a database and stored in one or more database storage disks, wherein the database comprises one or more database data objects, wherein the database is accessed via a contiguous data space representation, the contiguous data space being represented by a plurality of concatenated sub-data spaces, wherein each sub-data space is a virtual data space of a maximum size that is addressable by a computer operating system, each sub-data space comprising a plurality of data segments, each data segment comprising a plurality of pages, wherein the pages in the contiguous data space representation are contiguous, each page comprising a known number of addressable storage locations, wherein the contiguous data space, the sub-data spaces, the data segments, and the pages are addressable by a database management system, wherein the address of a page to be modified has been determined to be placed in a sub-data space, the method comprising the steps of:

(1) mapping a data segment of the data object from a database storage disk to a data segment of the sub-data space, wherein said data segment from said database storage disk contains the page to be modified;

(2) creating a modified section bit map for the sub-data space, wherein said modified section bit map comprises a plurality of bits, each bit representing a group of pages of the sub-data space and indicating whether one or more pages in said group has been modified;

(3) indicating that the page to be modified has been modified, thereby creating a modified page, by setting a bit in said modified section bit map to a predetermined value, wherein said bit represents a group containing said modified page;

(4) generating a modified section count representing a number of bits in said modified section bit map that are equal to said predetermined value; and

(5) issuing an asynchronous request to save one or more groups of pages of the sub-data space corresponding to bits in said modified section bit map that are equal to said predetermined value when said modified section count corresponds to a modified section threshold;

wherein, if the page to be modified requires a new mapping to said database storage disk, the method comprising the further steps of;

(6) copying the page to be modified to another work space in computer memory and modifying the page to be modified in said another work space in computer memory;

(7) allocating a new database storage page in said database storage disk;

(8) determining whether a mapping request to map the page to be modified to said new database storage page in said database storage disk can be combined with a prior mapping request, wherein said prior mapping request maps a second page in the sub-data space to a second database storage page in said database storage disk and the page to be modified is adjacent to said second page in the sub-data space;

(9) issuing said prior mapping request if step (8) determines that said mapping request cannot be combined with said prior mapping request and said prior mapping request exists;

(10) copying said second page of said prior mapping request from said another work space in computer memory if step (9) issues said prior mapping request;

(11) preparing said mapping request if step (9) issues said prior mapping request or said prior mapping request does not exist; and

(12) combining said mapping request with said prior mapping request if step (8) determines that said mapping request can be combined with said prior mapping request.

4. A computer system for modifying a page of a data object contained in a database and stored in one or more database storage disks, wherein the database comprises one or more database data objects, wherein the database is accessed via a contiguous data space representation, the contiguous data space being represented by a plurality of concatenated sub-data spaces, wherein each sub-data space is a virtual data space of a maximum size that is addressable by a computer operating system, each sub-data space comprising a plurality of data segments, each data segment comprising a plurality of pages, wherein the pages in the contiguous data space representation are contiguous, each page comprising a known number of addressable storage locations, wherein the contiguous data space, the sub-data spaces, the data segments, and the pages are addressable by a database management system, wherein the address of a page to be modified has been determined to be placed in a sub-data space, comprising:

mapping means for mapping a data segment of the database data object from a database storage disk to a data segment of the sub-data space, wherein said data segment from said database storage disk contains the page to be modified;

bit map means for creating a modified section bit map for the sub-data space, wherein said modified section bit map comprises a plurality of bits, each bit representing a group of pages of the sub-data space and indicating whether one or more pages in said group has been modified;

indicating means for indicating that the page to be modified has been modified, thereby creating a modified page, by setting a bit in said modified section bit map to a predetermined value, wherein said bit represents a group containing said modified page;

generating means for generating a modified section count representing the number of bits in said modified section bit map that are equal to said predetermined value; and

issuing means for issuing an asynchronous request to save one or more groups of pages of the sub-data space corresponding to bits in said modified section bit map that are equal to said predetermined value when said modified section count corresponds to a modified section threshold.

5. The computer system according to claim 4, wherein if the page to be modified requires a new mapping to said database storage disk, further comprising:

first copying means for copying the page to be modified to another work space in computer memory and modifying the page to be modified in said another work space in computer memory;

allocating means for allocating a new database storage page in said database storage disk;

determining means for determining whether a mapping request to map the page to be modified to said new database storage page in said database storage disk can be combined with a prior mapping request, wherein said prior mapping request maps a second page in the sub-data space to a second database storage page in said database storage disk and the page to be modified is adjacent to said second page in the sub-data space;

issuing means for issuing said prior mapping request if said determining means determines that said mapping request cannot be combined with said prior mapping request and said prior mapping request exists;

second copying means for copying said second page of said prior mapping request from said another work space in computer memory if said issuing means issues said prior mapping request;

preparing means for preparing said mapping request if said issuing means issues said prior mapping request or said prior mapping request does not exist; and

combining means for combining said mapping request with said prior mapping request if said determining means determines that said mapping request can be combined with said prior mapping request.

6. The computer system according to claim 4, further comprising:

second issuing means for issuing a synchronous request to save one or more groups of pages of each said sub-data space corresponding to bits in each said modified section bit map that are equal to said predetermined value when the database management system determines that a checkpoint is required, wherein the database management system waits for all outstanding asynchronous requests to complete.