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Claims  |
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What is claimed is:
1. An apparatus for virtual memory mapping for a computer system having at
least one permanent storage device for storing data, a virtual memory
system defining a virtual address space and including at least one cache
memory for temporarily storing data addressed by physical addresses, and a
processing unit, the processing unit including means for requesting data
utilizing a virtual address to access said data in the at least one cache
memory, the virtual memory system including means for mapping virtual
addresses to physical addresses, and means for detecting when access to
data requested by the means for requesting is not permitted at the virtual
address utilized by the means for requesting, said apparatus comprising:
means, operative in response to a detection by said means for detecting
that access to the requested data is not permitted, for determining if the
requested data is in the at least one cache memory,
means for transferring the requested data from the at least one permanent
storage device to the at least one cache memory, operative in response to
a determination by said means for determining that the requested data is
not in the at least one cache memory, and
means, operative in response to a determination that the requested data is
in the at least one cache memory, for instructing the means for mapping to
map the virtual address of the requested data to the physical address of
the requested data in the at least one cache memory and for permitting
access to the requested data.
2. An apparatus as set forth in claim 1, wherein the means for detecting
detects when a virtual address utilized to access data requested by the
means for requesting is not mapped to a physical address.
3. An apparatus as set forth in claim 2, wherein said requested data
includes a pointer containing a persistent address, the apparatus further
comprising means for relocating inbound the persistent address to a
virtual address.
4. An apparatus as set forth in claim 3, further comprising:
means for determining whether the virtual address utilized by the means for
requesting is assigned to data, and
means for signalling an error to the means for requesting, in response to a
determination that the virtual address utilized is not assigned to data.
5. An apparatus as set forth in claim 4, wherein the data resides in a
database, the apparatus further comprising:
means for determining if virtual addresses have been assigned to a selected
portion of the database, which selected portion contains the requested
data, and
means for assigning virtual addresses for said selected portion of the
database if such virtual addresses are not assigned.
6. An apparatus as set forth in claim 5 wherein the processing unit runs
application programs requiring data from the database, and wherein an
application program may involve a transaction, and including means,
operative when the transaction commits, for relocating outbound all data
which was relocated inbound during the transaction, and for unmapping all
mapped virtual address which were mapped to physical addresses during the
transaction, and for cancelling all virtual address assignments made
during the transaction.
7. An apparatus as set forth in claim 6 including means for locking a
portion of the database at a client computer when data from the portion is
utilized in a transaction at the client computer.
8. An apparatus as set forth in claim 7 wherein said means for relocating,
unmapping and cancelling, operative when a transaction commits, further
includes means for unlocking the locked portion of the database.
9. An apparatus as set forth in claim 1 wherein a request for data may be
one of a read request and a write request, wherein the database is divided
into segments, each segment containing at least one page and wherein said
means for transferring transfers a page containing the requested data
wherein the apparatus further comprises:
means, operative in response to a transfer of a page in response to a read
request for the page, for encaching the page for read and for locking the
page for read at a client computer, and means, operative in response to a
transfer of a page in response to a write request for the page, for
encaching the page for write and for locking the page for write at the
client computer.
10. An apparatus as set forth in claim 9 wherein the database system has a
plurality of client computers and a server computer for each of the at
least one permanent storage means, wherein the apparatus further
comprises:
second means, operative in response to a request for data from the at least
one database for read access from the means for requesting of a first
client computer, for detecting if the requested data is in the cache
memory of a second client computer for write access,
means, responsive to a detection by the means for detecting that the
requested data is in the cache memory of the second client computer, for
instructing the second client computer to downgrade a cached state of the
data to read access, and
means for permitting the means for transferring to transfer the requested
data to the first client computer.
11. An apparatus as set forth in claim 10 wherein each server computer has
an ownership table having an entry for each page of the at least one
permanent storage device of the server computer which is encached at a
client computer, said entry for a page indicating which client computers
have the page encached and whether the page is encached for one of read
and write access, and wherein the second means for detecting utilizes the
ownership table to determine if the page is encached at a client computer
for write.
12. An apparatus as set forth in claim 11 further comprising:
means for querying the client computer having a page encached for write to
determine if the page is locked for write, and
means, responsive to a response from the queried client computer that the
page is not locked for write, for downgrading the entry for the page in
the ownership table from indicating encached for write to indicate
encached for read and for permitting the means for transferring to
transfer the page to the cache memory of the first client computer.
13. An apparatus as set forth in claim 12, wherein the database system has
an application program involving at least one transaction, wherein the
apparatus further comprises:
means, responsive to a response from the queried client computer that the
page is locked for write, for deferring further action until the
transaction being run at the queried client computer commits, said means
for downgrading and for permitting being operative when the transaction
performed by the queried client computer commits.
14. An apparatus as set forth in claim 13 wherein each client computer has
a cache directory having an entry for each page in the corresponding cache
memory, which entry indicates a cached state and a locked state of the
page wherein the apparatus further comprises:
means, responsive to a query whether the cached state of a page is locked
write, for looking up the page in the cache directory of the queried
client computer to determine if the page is locked for write.
15. An apparatus as set forth in claim 14 wherein the queried client
computer includes means, responsive to a determination that the page is
not locked for write for downgrading the cached state of the entry for the
page in the cache directory from indicating encached for write to indicate
encached for read, and for replying to the querying server computer that
the page is not locked for write.
16. An apparatus as set forth in claim 15, wherein the queried client
computer includes means, responsive to a determination that the page is
locked for write, for marking the entry for the page in the cache
directory to be downgraded when the transaction commits, said means for
downgrading and replying being operative when the transaction being run on
the queried client computer commits.
17. An apparatus as set forth in claim 9 wherein the computer system has a
plurality of client computers and a server computer for each permanent
storage means, wherein the apparatus further comprises:
means, responsive to a request for data from a database for write access
from the means for requesting of a first client computer, for detecting if
the requested data is in the cache memory of a second client computer,
means, responsive to a detection by the means for detecting that the
requested data is in the cache memory of the second client computer, for
instructing the second client computer to remove the data from its cache
memory, and
means, for transferring the requested data to the first client computer.
18. An apparatus as set forth in claim 17, wherein each server computer has
an ownership table having an entry for each page of the permanent storage
means of the server computer which is encached at a client computer, said
entry for a page indicating which client computers have the page encached
and whether the page is encached for read or write, and wherein the means
for detecting utilizes the ownership table to determine if the page is
encached.
19. An apparatus as set forth in claim 18, further comprising:
means for querying each client computer having the page encached to
determine if the page is also locked,
means, responsive to a reply from all queried client computers that the
page is not locked, for removing entries for the page from the ownership
table, for making an entry for the requesting client computer in the
ownership table, and for permitting the means for transferring to transfer
the page to the cache memory of the requesting client computer.
20. An apparatus as set forth in claim 19 wherein the database system has
an application program involving at least one transaction wherein the
apparatus further comprises:
means, responsive to a response from at least one queried client computer
that the page is locked, for deferring further action until the at least
one transaction being run on the at least one queried client computer
commits, said means for removing all entries, and for making an entry and
for permitting being operative when the at least one transaction being run
on the at least one queried client computer commit.
21. An apparatus as set forth in claim 20 wherein each client computer has
a cache directory having an entry for each page in the corresponding cache
memory, which entry indicates a cached state and a locked state of the
page wherein the apparatus further comprises:
means, operative in response to a query as to whether a page is locked, for
looking up the page in the cache directory of the queried client computer
to determine if the page is locked.
22. An apparatus as set forth in claim 21 wherein the queried client
computer includes means, responsive to a determination that the page is
unlocked, for removing the page from the cache memory of the client
computer, for removing the entry for the page from the cache directory,
and for replying to the querying server computer that the page is not
locked.
23. An apparatus as set forth in claim 22 wherein the queried client
computer includes means, responsive to a determination that the page is
locked, for marking the entry for the page in the cache directory to be
evicted when the transaction commits, and for replying to the querying
server computer that the page is locked, said means for removing the page,
and for removing the entry, and for replying, being operative when the
transaction being run on the queried client computer commits.
24. An apparatus as set forth in claim 3 wherein the database system has a
computer for each of the at least one permanent storage means, wherein
each database is divided into segments, each containing at least one page,
and wherein each segment of a database is divided into a data segment and
an information segment.
25. An apparatus as set forth in claim 24 wherein a plurality of different
types of objects may be stored in a data segment, and wherein the
information segment for each data segment contains a tag table having a
tag entry for each object in the data segment, each tag entry identifying
at least the object type for the corresponding object.
26. An apparatus as set forth in claim 25 wherein a data segment may
contain at least one of a single object, a vector of multiple objects and
free space, wherein the tag entry for a single object contains a type code
for the object, the tag entry for a vector of objects contains a type code
for one of the multiple objects and a length field indicating a number of
objects in the vector, and the tag entry for free space has a type code
and a length field.
27. An apparatus as set forth in claim 26 wherein the database system has
an application program involving at least one transaction, and wherein
objects may be created during a transaction, an object having an object
type indication and an indication of a database and a segment for the
object wherein the apparatus further comprises:
means for determining the size of the object from the object type
indication,
means for searching the tag table to find free space of suitable size for
the object,
means for inserting a tag entry for the object in place of any tag entry
for free space if suitable free space is found,
means for inserting a tag entry for free space of shorter size if free
space remains after insertion of the object,
means for creating a tag entry at the end of the tag table if suitable free
space is not found, and
means for generating a virtual address for the object.
28. An apparatus as set forth in claim 27, wherein objects may be deleted
during a transaction, and further comprising:
means for finding a tag entry in the tag table for a deleted object,
means for determining the size of the deleted object, and
means for converting the tag entry for the deleted object to a tag entry
for free space of size equal to the determined size of the deleted object.
29. An apparatus as set forth in claim 28 further comprising:
means for determining if a tag entry preceding or following the tag entry
for free space for the deleted object in the tag table is a tag entry for
free space, and
means for merging adjacent tag entries for free space into a single tag
entry for free space of size equal to the sum of the sizes of the merged
tag entries.
30. An apparatus as set forth in claim 25 wherein each object in the at
least one database may contain at least one pointer at a selected offset
location in the object which points to a persistent address in the at
least one database, and wherein each database has a schema associated
therewith, the schema containing an entry for each object type present in
the database, each schema entry containing a field indicating a size of
the object type, and an instruction indicating an offset location in the
object for each pointer for the object type.
31. An apparatus as set forth in claim 30 further comprising:
means for transferring the schema for a database to a client computer
before the means for mapping at the client computer performs any mapping
for data from the database, and wherein the means for transferring
includes means for transferring page data from both a data segment and an
information segment corresponding to the data segment.
32. An apparatus as set forth in claim 31 wherein the database system has
an application program involving at least one transaction, and wherein the
apparatus further comprises:
means, operative when a transaction commits, for relocating outbound data
which was relocated inbound during the transaction;
wherein means for relocating inbound and the means for relocating outbound
each include means for determining an object type for a selected object
from the tag table transferred with a page, means for obtaining a
description of the selected object from the schema using the object type
from the tag table, and means for retrieving a corresponding pointer,
utilizing each schema instruction for the object type,
wherein the means for relocating inbound includes means for converting the
persistent address of each pointer to a corresponding virtual address, and
wherein the means for relocating outbound includes means for converting the
virtual address of each pointer to the corresponding persistent address.
33. An apparatus as set forth in claim 24 further comprising:
a persistent relocation map (PRM) in an information segment of a database,
which PRM indicates a beginning persistent address for a selected database
portion and having a given segment and offset,
said means for transferring including means for transferring the PRM, and
means for determining a persistent address corresponding to a given
database, segment and offset from the PRM.
34. An apparatus as set forth in claim 33 further comprising:
a virtual address map at least one client computer for indicating a
beginning virtual address for a selected database portion and having a
given offset, and
means for determining a virtual address corresponding to a given database,
segment and offset from the virtual address map.
35. An apparatus as set forth in claim 34 wherein the database system has
an application program involving at least one transaction, and wherein the
apparatus further comprises:
means, operative when a transaction commits, for relocating outbound data
which was relocated inbound during the transaction, and
means for relocating inbound including means for determining a database,
segment and offset for a given persistent page address from the persistent
relocation map, and means for determining the corresponding virtual page
address for the determined database, segment and offset from the virtual
address map, and
wherein the means for relocating outbound includes means for determining a
database, segment and offset for a given virtual page address from the
virtual address map, and means for determining a corresponding persistent
address from the determined database, segment and offset from the virtual
address map.
36. An apparatus as set forth in claim 35 further including:
means for verifying that the persistent relocation map for the segment
containing requested data has been transferred to the client computer,
means for examining each PRM entry in turn to determine if there is a
corresponding virtual address map entry, and
means for creating a new virtual address map entry for each selected
database portion for which a VAM entry does not exist.
37. An apparatus as set forth in claim 1 wherein the means for detecting
that access to the requested data is not permitted is operative in
response to one of an instruction indicating access to data is not
permitted and a program fault resulting from an unsuccessful attempt to
one of read and write data.
38. A method for virtual memory mapping and transaction management for a
database system having at least one permanent storage means for storing
data in at least one database, a virtual memory system defining a virtual
address space and including at least one cache memory for temporarily
storing data addressed by physical addresses and means for mapping virtual
addresses to physical addresses, and a processing unit, the processing
unit including means for requesting data utilizing a virtual address to
access said data in the at least one cache memory, said method comprising
the steps of:
detecting, using the virtual memory system, when access to data requested
by the means for requesting is not permitted at the virtual address
utilized by the means for requesting,
determining if the requested data is in the at least one cache memory in
response to a detection that access to the requested data is not
permitted,
transferring the requested data from the at least one permanent storage
means to the at least one cache memory, when the requested data is not in
the at least one cache memory,
instructing the means for mapping to map the virtual address of the
requested data to the physical address of the requested data in the at
least one cache memory, and
permitting access to the requested data.
39. A method as set forth in claim 38, wherein the step of detecting
comprises detecting whether the virtual address utilized to access the
data requested by the means for requesting is mapped to a physical
address.
40. A method as set forth in claim 39, wherein the requested data includes
pointers containing persistent addresses, and the method further comprises
the step of relocating inbound the pointers in the requested data from
persistent addresses to virtual addresses.
41. A method as set forth in claim 40, further comprising the steps of:
determining whether the virtual address utilized by the means for
requesting is assigned to a portion of the at least one database, and
signalling an error to the means for requesting in response to a
determination that the virtual address utilized is not assigned to a
portion of the at least one database.
42. A method as set forth in claim 41, further comprising the steps of:
determining if virtual addresses have been assigned to a selected portion
of a database, which selected portion contains the requested data, and
assigning virtual addresses for said selected portion if such virtual
addresses are not assigned.
43. A method as set forth in claim 42 wherein the processing unit runs
application programs requiring data from said at least one database, and
wherein an application program may involve one or more transactions, said
method further comprising the steps, performed when a transaction of the
one or more transactions commits, of:
relocating outbound all data which was relocated inbound during the
transaction,
unmapping all physical addresses which were mapped during said transaction,
and
cancelling all virtual address assignments made during the transaction.
44. A method as set forth in claim 43 including the step of locking a
portion of the at least one database at a client computer when data from
the portion is utilized in a transaction at the client computer.
45. A method as set forth in claim 44 further including the step of
unlocking all portions of the at least one database which were locked
during the transaction when the transaction commits.
46. A method as set forth in claim 38 wherein a request for data may be one
of a read request and a write request, wherein a database is divided into
segments, each segment containing one or more pages, and wherein the step
of transferring transfers the page containing requested data, said method
further comprising the steps of:
encaching a transferred page for read in response to a transfer for a read
request and locking the page for read at a client computer, and
encaching a transferred page for write in response to a transfer for a
write request and locking the page for write at the client computer.
47. A method as set forth in claim 46 wherein the database system has a
plurality of client computers and a server computer for each of the at
least one permanent storage means, said method further comprising the
steps of:
detecting, in response to a request for data from a database for read
access from the means for requesting of a first client computer, if the
requested data is in the cache memory of a second client computer, and
instructing the second client computer, in response to a detection that the
requested data is in the cache memory of the second client computer, to
downgrade the encached state of the data to read access.
48. A method as set forth in claim 47 wherein each server computer has an
ownership table having an entry for each page of the at least one
permanent storage means of the server computer which is encached at the
client computer, each entry for a page indicating which client computers
have the page encached and whether the page is encached for one of read
and write access, and wherein the step of detecting includes the step of
utilizing the ownership table to determine if the page is encached for
write access.
49. A method as set forth in claim 48 further comprising the steps of:
querying the client computer having the page encached for write to
determine if the page is locked for write, and
downgrading the entry for the page in the ownership table from indicating
encached for write to indicate encached for read in response to a response
from the queried client computer that the page is not locked for write.
50. A method as set forth in claim 49, wherein an application program
involves at least one transaction, said method further comprising the step
of:
deferring further steps, in response to a response from the queried client
computer that the page is locked for write, until the transaction being
run at the queried client computer commits, the steps of downgrading and
transferring being performed when the transaction performed by the queried
client computer commits.
51. A method as set forth in claim 50 wherein each client computer has a
cache directory having an entry for each page in the corresponding cache
memory, which entry indicates a cached state and a locked state of the
page, said method further comprising the step of:
looking up the page in the cache directory of the queried client computer
to determine if the page is locked for write in response to a query of the
locked state of the page.
52. A method as set forth in claim 51 further comprising the steps of:
downgrading the cached state of the entry for the page in the cache
directory of the queried client computer from indicating encached for
write to indicate encached for read in response to a determination that
the page is not locked for write, and
replying to the querying server computer that the page is not locked for
write.
53. A method as set forth in claim 52, including the steps of:
marking the entry for the page in the cache directory of the queried client
computer to be downgraded when the transaction commits in response to a
determination that the page is locked for write,
the steps of downgrading and replying being performed when the transaction
being run on the queried client computer commits.
54. A method as set forth in claim 46 wherein the database system has a
plurality of client computers and a server computer for each of the at
least one permanent storage means, said method further comprising the
steps of:
detecting if the requested data is in the cache memory of a second client
computer in response to a request for data from a database for write
access from the means for requesting of a first client computer; and
instructing the second client computer, in response to a detection that the
requested data is in the cache memory of the second client computer, to
remove the data from the cache memory of the second client computer.
55. A method as set forth in claim 54, wherein each server computer has an
ownership table having an entry for each page of the permanent storage
means of the server computer which is encached at a client computer, each
entry for a page indicating which client computers have the page encached
and whether the page is encached for one of read and write access, and
wherein the step of detecting includes a step of determining if the page
is encached utilizing the ownership table.
56. A method as set forth in claim 55 further comprising the steps of:
querying each client computer having the page encached to determine if the
page is also locked,
removing all entries for the page from the ownership table in response to a
reply from all queried client computers that the page is not locked, and
making an entry for the requesting client computer in the ownership table.
57. A method as set forth in claim 56 wherein the database system has an
application program involving at least one transaction, said method
further comprising the steps of:
deferring further action, in response to a response from at least one
queried client computer that the page is locked, until the transactions
being run on all said at least one queried client computers commit,
the steps of removing all entries, making an entry and for transferring the
page being performed when the transactions being run on all queried client
computers commit.
58. A method as set forth in claim 57 wherein each computer has a cache
directory having an entry for each page in the corresponding cache memory,
which entry indicates a cached state and a locked state of the page, the
method further comprising the step of:
looking up the page in the cache directory of the queried client computer
to determine if the page is locked in response to a query of the locked
state of the page.
59. A method as set forth in claim 58 further comprising the steps of:
removing the page from the cache memory of the queried client computer in
response to a determination that the page is in the cache memory,
removing the entry for the page from the cache directory, and
replying to the server computer that the page is not locked.
60. A method as set forth in claim 59 further comprising the steps of:
marking the entry for the page in the cache directory of the queried client
computer to be evicted when the transaction commits in response to a
determination that the page is locked, and
replying to the querying server computer that the page is locked, said
steps of removing the page, removing the entry, and replying being
performed when the transaction being run on the queried client computer
commits.
61. A method as set forth in claim 38 wherein the database system includes
an application program involving at least one transaction, and wherein
objects may be created during a transaction, an object having an object
type indication and an indication of a database and a segment of a
database for the object, said method further comprising the steps of:
utilizing the object type indication of an object to determine the size of
the object,
searching a tag table for free space tags to find free space of suitable
size for the object,
inserting an object tag for the object in place of the free space tag if
suitable free space is found,
inserting a free space tag of shorter size if free space remains after
insertion of the object,
creating an object tag at the end of the tag table if suitable free space
is not found, and
generating a virtual address for the object.
62. A method as set forth in claim 61 wherein objects may be deleted during
a transaction, said method further comprising the steps of:
finding a tag in a tag table for a deleted object, determining a size of
the deleted object, and
converting the tag for the deleted object to a free space tag of a size
equal to the determined size of the deleted object.
63. An method as set forth in claim 62 further comprising the steps of:
determining if a tag preceding or following the free space tag is a free
space tag, and
merging adjacent free space tags into a single free space tag of a size
equal to the sum of sizes of the merged tags.
64. A method as forth in claim 40 including the steps of:
transferring a schema for a database to a client computer before relocating
data from the database at the client computer, and
wherein the step of transferring includes the step of transferring page
data from both a data segment and a corresponding information segment.
65. A method as set forth in claim 64 wherein the database system includes
an application program involving at least one transaction, said method
further comprising the steps of:
relocating outbound, when a transaction commits, all data which was
relocated inbound during the transaction,
wherein the step of relocating inbound and the step of relocating outbound
each include the step of determining an object type for a selected object
utilizing a page table transferred with a page,
obtaining a description of the selected object from the schema, utilizing
the object type from a tag table, and
wherein the step of relocating inbound includes a step of converting a
persistent address of each pointer to a corresponding virtual address, and
wherein the step of relocating outbound includes a step of converting a
virtual address of each pointer to a corresponding persistent address.
66. A method as set forth in claim 40 wherein the database system includes
a persistent relocation map (PRM) in an information segment of a database,
which PRM indicates a persistent address of a beginning of a selected
database portion and has a given segment and offset, wherein the step of
transferring includes a step of transferring the PRM, said method further
including a step of determining a persistent address corresponding to a
given database, segment and offset utilizing the PRM.
67. A method as set forth in claim 66 wherein the database system includes
a virtual address map (VAM) at at least one client computer, which virtual
address map indicates a beginning virtual address for a selected database
portion and having a given segment and offset, said method further
including a step of determining a virtual address corresponding to a given
database, segment and offset utilizing the VAM.
68. A method as set forth in claim 67 wherein the database system includes
an application program involving at least one transaction, said method
further comprising the steps of:
relocating outbound, when a transaction commits, all data which was
relocated inbound during the transaction,
wherein the step of relocating inbound comprises the steps of determining a
database, segment and offset for a given persistent page address utilizing
the PRM, and determining a corresponding virtual page address from the
determined database, segment and offset, utilizing the VAM; and
wherein the step of relocating outbound includes the steps of determining a
database, segment and offset for a given virtual page address utilizing
the VAM, and determining a corresponding persistent page address from the
determined database, segment and offset utilizing the PRM.
69. A method as forth in claim 68 wherein said step of assigning includes
the steps of:
verifying that the PRM for the segment containing requested data has been
transferred to the client computer,
determining if there is a corresponding VAM entry for each PRM entry, and
creating a new VAM entry, for each selected database portion for which it
is determined that a VAM entry does not exist.
70. A method as set forth in claim 38 wherein a step of detecting that data
is not available includes detecting one of whether data is not available
and whether a program fault resulted from an unsuccessful attempt to
access data.
71. The apparatus as set forth in claim 1, wherein the database defines an
address space which is larger than the virtual address space.
72. An apparatus for virtual memory mapping for a computer system having a
permanent storage device for storing data, a virtual memory system
defining a virtual address space and including a cache memory for
temporarily storing data addressed by physical addresses, and a processing
unit, the processing unit including a data requesting mechanism that
requests data utilizing a virtual address to access said data in the cache
memory, the virtual memory system including a virtual memory map that maps
virtual addresses to physical addresses, and a virtual memory fault
detector that detects when access to data requested by the data requesting
mechanism is not permitted at the virtual address utilized by the data
requesting mechanism, said apparatus comprising:
a status detection mechanism having an input coupled to the virtual memory
fault detector for receiving an indication therefrom that access to the
requested data is not permitted, and an output for outputting a
determination indicating whether the requested data is in the cache
memory,
a data transfer controller coupled between the permanent storage device and
the cache memory, and having an input coupled to the status detection
mechanism, which transfers the requested data from the permanent storage
device to the cache memory when the input receives a determination by said
status detection mechanism that the requested data is not in the cache
memory, and
a mapping instruction device having an input coupled to the data transfer
controller, and an output coupled to the virtual memory system, the
mapping instruction device instructing the virtual memory system, to map
the virtual address of the requested data to the physical address of the
requested data in the cache memory and permitting access to the requested
data when a determination that the requested data is in the cache memory
is received.
73. An apparatus as set forth in claim 72, wherein the virtual memory fault
detector detects when a virtual address utilized to access data requested
by the data requesting mechanism is not mapped to a physical address.
74. An apparatus as set forth in claim 73, wherein said requested data
includes a pointer containing a persistent address, and further comprising
an inbound address relocation mechanism that relocates the persistent
address into a virtual address.
75. An apparatus as set forth in claim 74, further comprising:
an address assignment determination mechanism that determines whether the
virtual address utilized by the data requesting mechanism is assigned to a
portion of the data stored on the permanent storage device, and
an error signalling device that signals an error to the data requesting
mechanism, in response to a determination that the virtual address
utilized is not assigned to a portion of the data stored on the permanent
storage device.
76. An apparatus as set forth in claim 75, further comprising:
an assignment status detection device that determines if virtual addresses
have been assigned to a selected portion of the data on the permanent
storage device, which selected portion contains the requested data, and
an address assignment device that assigns virtual addresses for said
selected portion of the data if such virtual addresses are not assigned.
77. An apparatus as set forth in claim 76, wherein the processing unit runs
application programs requiring data from the permanent storage device, and
wherein an application program may involve one or more transactions, and
including an outbound relocation mechanism that relocates outbound all
data which was relocated inbound during said transaction when a
transaction of the one or more transactions commits, and that unmaps all
the mapped physical addresses which were mapped during said transaction,
and that cancels all virtual address assignments made during the
transaction.
78. An apparatus as set forth in claim 77, including a locking mechanism
that locks a portion of the data at a client computer when data from the
portion is utilized in a transaction at the client computer.
79. An apparatus as set forth in claim 78, wherein said outbound relocation
mechanism further includes an unlocking mechanism that unlocks the locked
portion of the data.
80. An apparatus as set forth in claim 72, wherein a request for data may
be one of a read request and a write request, wherein the data is
organized into a database which is divided into segments, each segment
containing at least one page and wherein the data transfer controller
transfers a page containing the requested data wherein the apparatus
further comprises:
a read request device having an input for receiving a transfer of a page in
response to a read request for the page, that encaches the page for read
and that locks the page for read at a client computer, and a write request
device having an input for receiving a transfer of a page in response to a
write request for the page, that encaches the page for write and locks the
page for write at the client computer.
81. An apparatus as set forth in claim 80, wherein the computer system has
a plurality of client computers and a server computer for the permanent
storage device, wherein the apparatus further comprises:
cache status detection mechanism having an input for receiving a request
for data from the at least one database for read access from the
requesting mechanism of a first client computer, for detecting if the
requested data is in the cache memory of a second client computer for
write access,
an instructing device having an input for receiving a detection by the
detecting device that the requested data is in the cache memory of the
second client computer, and an output for instructing the second client
computer to downgrade a cached state of the data to read access, and
wherein the data transfer controller transfers the requested data to the
first client computer.
82. An apparatus as set forth in claim 81, wherein each server computer has
an ownership table having an entry for each page of the permanent storage
device of the server computer which is encached at a client computer, said
entry for a page indicating which client computers have the page encached
and whether the page is encached for one of read and write access, and
wherein the cache status detection mechanism utilizes the ownership table
to determine if the page is encached for write.
83. An apparatus as set forth in claim 82, further comprising:
a querying device that queries the queried client computer having a page
encached for write to determine if the page is locked for write, and
a status downgrading mechanism having an input for receiving a response
from the queried computer that the page is not locked for write, that
downgrades the entry for the page in the ownership table from indicating
encached for write to indicate encached for read and that permits the data
transfer controller device to transfer the page to the cache memory of the
first client computer.
84. An apparatus as set forth in claim 83, wherein the computer system has
an application program involving at least one transaction, wherein the
apparatus further comprises:
a delay mechanism having an input for receiving a response from the queried
client computer that the page is locked for write, that defers further
action until the transaction being run at the queried client computer
commits, said status downgrading mechanism being operative when the
transaction performed by the queried client computer commits.
85. An apparatus as set forth in claim 84, wherein each client computer has
a cache directory having an entry for each page in the corresponding cache
memory, which entry indicates a cached state and a locked state of the
page wherein the apparatus further comprises:
a look-up device having an input that receives a query whether the cached
state of a page is locked write, that looks up the page in the cache
directory of the queried client computer to determine if the page is
locked for write.
86. An apparatus as set forth in claim 85, wherein the queried client
computer includes a downgrading and replying mechanism having an input for
receiving a determination that the page is not locked for write, that
downgrades the cached state of the entry for the page in the cache
directory from indicating encached for write to indicate encached for
read, and replies the querying server computer that the page is not locked
for write.
87. An apparatus as set forth in claim 86, wherein the queried client
computer includes a marking device having an input for receiving a
determination that the page is locked for write, that marks the entry for
the page in the cache directory to be downgraded when the transaction
commits, the downgrading and replying device being operative when the
transaction being run on the queried client computer commits.
88. An apparatus as set forth in claim 80, wherein the database system has
a plurality of client computers and a server computer for each permanent
storage device, wherein the apparatus further comprises:
a detection device having an input for receiving a request for data for
write access from the data requesting device of a first client computer,
that detects if the requested data is in the cache memory of a second
client computer,
an instruction device having an input for receiving a detection by the
detection device that the requested data is in the cache memory of the
second client computer, and an output for instructing the second client
computer to remove the data from its cache memory, and
wherein the data transfer controller transfers the requested data to the
first client computer.
89. An apparatus as set forth in claim 88, wherein each server computer has
an ownership table having an entry for each page of the permanent storage
device of the server computer which is encached at a client com | | |
