Storage-side storage request management

• US 8,521,923 B2
• Filed: 03/12/2012
• Issued: 08/27/2013
• Est. Priority Date: 09/19/2008
• Status: Active Grant

• Current Assignee: Oracle International Corporation (Oracle Corporation)
• Original Assignee: Oracle International Corporation (Oracle Corporation)
• Inventors: Lee, Sue K., Kolla, Vivekananda C., Shah, Akshay D., Chatterjee, Sumanta, Susairaj, Margaret, Loaiza, Juan R., Tsukerman, Alexander, Subramaniam, Sridhar
• Primary Examiner(s): Alrobaye, Idriss N
• Assistant Examiner(s): LEWIS-TAYLOR, DAYTON A.
• Application Number:
  US13/418,150
• Publication Number:
  US 20120173774A1
• Time in Patent Office: 533 Days
• Field of Search: None
• US Class Current: 710/39
• CPC Class Codes: G06F 12/00 Accessing, addressing or allocating within memory systems or architectures digital input from, or digital output to record carriers, e.g. to disk storage units, G06F3/06
• CPC Class Codes: G06F 16/2255 Hash tables
• CPC Class Codes: G06F 16/24557 Efficient disk access during query execution
• CPC Class Codes: G06F 16/2456 Join operations
• CPC Class Codes: G06F 3/0611 in relation to response time
• CPC Class Codes: G06F 3/0659 Command handling arrangements, e.g. command buffers, queues, command scheduling
• CPC Class Codes: G06F 3/067 Distributed or networked storage systems, e.g. storage area networks [SAN], network attached storage [NAS]

Abstract

Techniques are provided for managing, within a storage system, the sequence in which I/O requests are processed by the storage system based, at least in part, on one or more logical characteristics of the I/O requests. The logical characteristics may include, for example, the identity of the user for whom the I/O request was submitted, the service that submitted the I/O request, the database targeted by the I/O request, an indication of a consumer group to which the I/O request maps, the reason why the I/O request was issued, a priority category of the I/O request, etc. Techniques are also provided for automatically establishing a scheduling policy within a storage system, and for dynamically changing the scheduling policy in response to changes in workload.

Claims

1. A method comprising:

receiving, at a storage system, input/output (I/O) requests to read data from or write data to one or more storage devices, the I/O requests including physical characteristics that indicate locations within the one or more storage devices of the data to be read or written;

queuing, within the storage system, a plurality of the I/O requests received by the storage system;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

wherein the one or more logical characteristics are not the physical characteristics;

wherein the one or more logical characteristics include, for at least a first I/O request of the particular I/O requests, an indication of at least one of;

a database name associated with the first I/0 request, the database name specified by request metadata that accompanies the first I/O request;

a workload type, the workload type categorizing work, performed by a first I/O requestor, for which the first I/O requestor issued the first I/O request;

or

a user name associated with a communication session responsive to which the first I/O requestor issued the first I/O request;

processing the particular I/O request in response to the storage server selecting the particular I/O request by reading data from or writing data to a location indicated by particular physical characteristics included in the particular I/O request;

wherein the method is performed by one or more computing devices.

2. The method of claim 1, further comprising receiving one or more selection policies from one or more database servers, the one or more selection policies indicating to the storage system how to select, from the queued plurality of the I/O requests, the particular I/O request to process.

3. The method of claim 2, further comprising:

the storage system grouping the plurality of I/O requests into one or more groups based on the one or more logical characteristics associated with the particular I/O requests in the plurality of the I/O requests;

the storage system applying the one or more selection policies to identify a particular group of the one or more groups from which to select the particular I/O request.

4. The method of claim 2, further comprising:

receiving from the one or more database servers, with the one or more selection policies, policy-to-phase assignment data indicating how the one or more selection policies are to be applied over a plurality of phases, wherein the one or more selection policies include a plurality of policies;

based at least on the policy-to-phase assignment data, identifying one or more first policies, of the one or more selection policies, to apply during one or more first phases of the plurality of phases;

during the one or more first phases, filtering the queued plurality of I/O requests by applying the identified one or more first policies, thereby yielding a filtered set of I/O requests;

based at least on the policy-to-phase assignment data, identifying a final policy, of the one or more selection policies, to apply during a final phase of the plurality of phases;

during a final phase of the plurality of phases, based on the policy-to-phase assignment data, selecting the particular I/O request from the filtered set of I/O requests by applying the final policy.

5. The method of claim 4, wherein identifying the one or more first policies or identifying the final policy is further based at least in part on which I/O requests remain unfiltered from the queued plurality of I/O requests after an immediately preceding phase.

6. The method of claim 4, wherein the policy-to-phase assignment data indicates that a first policy of the one or more first policies is based upon I/O requests that are grouped in part by database names, and that the final policy is based upon I/O requests that are grouped in part by workload type or consumer group.

7. The method of claim 2, further comprising:

receiving, at the storage system, an instruction from a database server to change the one or more selection policies.

8. The method of claim 7, wherein the instruction indicates a triggering event, in response to which the storage system is to change the one or more selection policies.

9. The method of claim 2, further comprising:

receiving from the one or more database servers, with the one or more selection policies, policy-to-disk assignment data indicating which selection policies are to be applied to which disks in the storage system.

10. The method of claim 2, further comprising:

receiving with the one or more selection policies data indicating a particular database, of the plurality of databases stored in the storage system, to which the one or more selection policies apply;

the storage system storing the one or more selection policies in association with the particular database;

the storage system selecting the particular I/O request to process in part by identifying a first group of I/O requests from which to select the particular I/O request, wherein identifying the first group comprises applying at least one of the one or more selection policies to a set of I/O requests that access the particular database.

11. The method of claim 10, further comprising receiving data indicating how to divide the set of I/O requests that access the particular database into a plurality of groups, including the first group, based on at least one logical characteristic, wherein the one or more selection policies indicate how to identify a group of the plurality of groups from which to select the particular I/O request.

12. The method of claim 1, further comprising:

the storage system dynamically adjusting a scheduling policy based upon the logical characteristics of the I/O requests, wherein the scheduling policy indicates when the storage system is ready to process pending I/O requests.

13. The method of claim 1, wherein the one or more logical characteristics include, for at least the first I/O request of the particular I/O requests, an indication of the workload type.

14. The method of Claim 13, further comprising:

receiving a mapping of workload types to groups;

grouping the plurality of I/O requests into a plurality of groups based on the mapping;

selecting the particular I/O request to process based on the particular I/O request belonging to a first group of the plurality of groups.

15. The method of claim 1, wherein the one or more logical characteristics include, for at least the first I/O request of the particular I/O requests, an indication of the user name.

16. The method of Claim 15, further comprising:

receiving a mapping of user names to groups;

grouping the plurality of I/O requests into a plurality of groups based on the mapping;

selecting the particular I/O request to process based on the particular I/O request belonging to a first group of the plurality of groups.

17. A method comprising:

receiving, at a storage system, from one or more database servers, input/output (I/O) requests to read data from or write data to one or more storage devices, the I/O requests indicating locations within the one or more storage devices of the data to be read or written;

wherein, for each of a plurality of databases within which the one or more database servers perform database operations, the one or more storage devices store at least some data;

wherein the I/O requests are accompanied by request metadata that at least specifies to which database of the plurality of databases that data involved in the I/O requests logically belong;

queuing, within the storage system, a plurality of the I/O requests;

when the storage system is ready to process a queued I/O request, a storage server within the storage system selecting which queued I/O request to process based on at least a first policy;

wherein the first policy distinguishes between I/O requests in part based on the databases to which the data involved in the I/O requests logically belong, as specified by the request metadata;

processing the queued I/O request that is selected based on the policy;

wherein the method is performed by one or more computing devices.

18. The method of claim 17, further comprising the storage system receiving an instruction to change the first policy from the one or more database servers.

19. The method of claim 17, wherein the first policy identifies at least a ratio of requests to process from a first set of one or more databases to requests to process from a second set of one or more databases.

20. The method of claim 17, further comprising:

storing the first policy in association with a particular database;

receiving data indicating how to divide a set of I/O requests that access the particular database into a plurality of groups based on at least one logical characteristic of the I/O requests, wherein the first policy indicates to the storage server how to identify a group of the plurality of groups from which to select a next I/O request to process.

49. The method of claim 17, further comprising:

receiving, at the one or more database servers, one or more database commands to manipulate or search for data objects in the plurality of databases;

at the database server, translating the one or more database commands into the I/O requests;

responsive to the I/O requests, receiving, at the database server, blocks of data from the storage system;

translating, at the database server, the blocks of data received from the storage system into the data objects, from the plurality of databases, referenced by the database commands;

executing, at the database server, the one or more database commands based on the data objects translated from the blocks of data received from the storage system.

21. A method of comprising:

receiving, at a storage system, from a database server, input/output (I/O) requests to read data from or write data to one or more storage devices;

queuing, within the storage system, a plurality of the I/O requests;

grouping the plurality of I/O requests into one or more groups based on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

wherein grouping the plurality of I/O requests comprises grouping a first set of I/O requests in the plurality of I/O requests into a first group based on one or more logical characteristics specified by the database server when issuing the first set of I/O requests, the one or more logical characteristics including at least one of;

a database name associated with the first set of I/O requests, the database name specified by request metadata that accompanies the first I/O request;

a workload type, the workload type categorizing work, performed by the database server, for which the database server issued the first set of I/O requests;

a consumer group, comprising a plurality of consumers, associated with the first set of I/O requests;

a user name associated with a communication session responsive to which the database server issued the first set of I/O requests;

a service through which the database server issued the first set of I/O requests;

or

a purpose for which the database server issued the first set of I/O requests;

receiving, at the storage system, one or more selection policies from the database server, the one or more selection policies specifying one or more ratios for the one or more groups;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on the one or more ratios and the group to which the particular I/O request belongs;

,

processing the particular I/O request in response to the storage server selecting the particular I/O request;

wherein the method is performed by one or more computing devices.

22. A method comprising:

receiving, at a storage system, from a database server, input/output (I/O) requests to read data from or write data to one or more storage devices;

queuing, within the storage system, a plurality of the I/O requests;

grouping the plurality of I/O requests into one or more groups based on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

receiving, at the storage system, one or more selection policies from the database server, the one or more selection policies specifying one or more ratios for the one or more groups;

receiving from the database server, with the one or more selection policies, policy-to-phase assignment data indicating how the one or more selection policies are to be applied over a plurality of phases, wherein the one or more selection policies include a plurality of policies;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on the one or more ratios and the group to which the particular I/O request belongs;

,

wherein selecting the particular I/O request comprises;

based at least on the policy-to-phase assignment data, identifying one or more first policies, of the one or more selection policies, to apply during one or more first phases of the plurality of phases;

during the one or more first phases, filtering the queued plurality of I/O requests by applying the identified one or more first policies, thereby yielding a filtered set of I/O requests;

based at least on the policy-to-phase assignment data, identifying a final policy, of the one or more selection policies, to apply during a final phase of the plurality of phases; and

during the final phase of the plurality of phases, based on the policy-to-phase assignment data, selecting a particular I/O request from the filtered set of I/O requests by applying the final policy;

processing the particular I/O request in response to the storage server selecting the particular I/O request;

wherein the method is performed by one or more computing devices.

23. The method of claim 22, wherein the final policy involves a final ratio of the one or more ratios that is different than any ratio involved in the one or more first policies.

24. A method comprising:

receiving, at a storage system, from a database server, input/output (I/O) requests to read data from or write data to one or more storage devices;

queuing, within the storage system, a plurality of the I/O requests;

grouping the plurality of I/O requests into one or more groups based on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

receiving, at the storage system, one or more selection policies from the database server, the one or more selection policies specifying one or more ratios for the one or more groups;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on the one or more ratios and the group to which the particular I/O request belongs;

,

wherein selecting the particular I/O request comprises;

based on the one or more ratios, identifying load usage allocations for a plurality of groups of I/O requests, the plurality of groups including the one or more groups;

based on load statistics, identifying actual load usages for the plurality of groups over a period of time;

identifying a particular group, of the one or more groups, whose actual load usage is further behind the load usage allocated to the particular group than any other group in the plurality of groups;

selecting the particular I/O request from the particular group

processing the particular I/O request in response to the storage server selecting the particular I/O request;

wherein the method is performed by one or more computing devices.

25. One or more non-transitory computer-readable media storing instructions which, when executed by one or more computing devices, cause:

receiving, at a storage system, input/output (I/O) requests to read data from or write data to one or more storage devices, the I/O requests including physical characteristics that indicate locations within the one or more storage devices of the data to be read or written;

queuing, within the storage system, a plurality of the I/O requests received by the storage system;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

wherein the one or more logical characteristics are not the physical characteristics;

wherein the one or more logical characteristics include, for at least a first I/O request of the particular I/O requests, an indication of at least one of;

a database name associated with the first I/O request, the database name specified by request metadata that accompanies the first I/O request;

a workload type, the workload type categorizing work, performed by a first I/O requestor, for which the first I/O requestor issued the first I/O request;

or

a user name associated with a communication session responsive to which the first I/O requestor issued the first I/O request;

processing the particular I/O request in response to the storage server selecting the particular I/O request by reading data from or writing data to a location indicated by particular physical characteristics included in the particular I/O request;

wherein the method is performed by one or more computing devices.

26. The one or more non-transitory computer-readable media of claim 25, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving one or more selection policies from one or more database servers, the one or more selection policies indicating to the storage system how to select, from the queued plurality of the I/O requests, the particular I/O request to process.

27. The one or more non-transitory computer-readable media of claim 26, wherein the instructions, when executed by the one or more computing devices, further cause:

the storage system grouping the plurality of I/O requests into one or more groups based on the one or more logical characteristics associated with the particular I/O requests in the plurality of the I/O requests;

the storage system applying the one or more selection policies to identify a particular group of the one or more groups from which to select the particular I/O request.

28. The one or more non-transitory computer-readable media of claim 26, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving from the one or more database servers, with the one or more selection policies, policy-to-phase assignment data indicating how the one or more selection policies are to be applied over a plurality of phases, wherein the one or more selection policies include a plurality of policies;

based at least on the policy-to-phase assignment data, identifying one or more first policies, of the one or more selection policies, to apply during one or more first phases of the plurality of phases;

during the one or more first phases, filtering the queued plurality of I/O requests by applying the identified one or more first policies, thereby yielding a filtered set of I/O requests;

based at least on the policy-to-phase assignment data, identifying a final policy, of the one or more selection policies, to apply during a final phase of the plurality of phases;

during a final phase of the plurality of phases, based on the policy-to-phase assignment data, selecting the particular I/O request from the filtered set of I/O requests by applying the final policy.

29. The one or more non-transitory computer-readable media of claim 28, wherein identifying the one or more first policies or identifying the final policy is further based at least in part on which I/O requests remain unfiltered from the queued plurality of I/O requests after an immediately preceding phase.

30. The one or more non-transitory computer-readable media of claim 28, wherein the policy-to-phase assignment data indicates that a first policy of the one or more first policies is based upon I/O requests that are grouped in part by database names, and that the final policy is based upon I/O requests that are grouped in part by workload type or consumer group.

31. The one or more non-transitory computer-readable media of claim 26, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving, at the storage system, an instruction from a database server to change the one or more selection policies.

32. The one or more non-transitory computer-readable media of claim 31, wherein the instruction indicates a triggering event, in response to which the storage system is to change the one or more selection policies.

33. The one or more non-transitory computer-readable media of claim 26, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving from the one or more database servers, with the one or more selection policies, policy-to-disk assignment data indicating which selection policies are to be applied to which disks in the storage system.

34. The one or more non-transitory computer-readable media of claim 26, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving with the one or more selection policies data indicating a particular database, of the plurality of databases stored in the storage system, to which the one or more selection policies apply;

the storage system storing the one or more selection policies in association with the particular database;

the storage system selecting the particular I/O request to process in part by identifying a first group of I/O requests from which to select the particular I/O request, wherein identifying the first group comprises applying at least one of the one or more selection policies to a set of I/O requests that access the particular database.

35. The one or more non-transitory computer-readable media of claim 34, wherein the instructions, when executed by the one or more computing devices, further cause receiving data indicating how to divide the set of I/O requests that access the particular database into a plurality of groups, including the first group, based on at least one logical characteristic, wherein the one or more selection policies indicate how to identify a group of the plurality of groups from which to select the particular I/O request.

36. The one or more non-transitory computer-readable media of claim 25, wherein the instructions, when executed by the one or more computing devices, further cause:

the storage system dynamically adjusting a scheduling policy based upon the logical characteristics of the I/O requests, wherein the scheduling policy indicates when the storage system is ready to process pending I/O requests.

37. The one or more non-transitory computer-readable media of claim 25, wherein the one or more logical characteristics include, for at least the first I/O request of the particular I/O requests, an indication of the workload type.

38. The one or more non-transitory computer-readable media of claim 37, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving a mapping of workload types to groups;

grouping the plurality of I/O requests into a plurality of groups based on the mapping;

selecting the particular I/O request to process based on the particular I/O request belonging to a first group of the plurality of groups.

39. The one or more non-transitory computer-readable media of claim 25, wherein the one or more logical characteristics include, for at least the first I/O request of the particular I/O requests, an indication of the user name.

40. The one or more non-transitory computer-readable media of claim 39, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving a mapping of user names to groups;

grouping the plurality of I/O requests into a plurality of groups based on the mapping;

selecting the particular I/O request to process based on the particular I/O request belonging to a first group of the plurality of groups.

41. One or more non-transitory computer-readable media storing instructions which, when executed by one or more computing devices, cause:

receiving, at the storage system, from one or more database servers, input/output (I/O) requests to read data from or write data to one or more storage devices, the I/O requests indicating locations within the one or more storage devices of the data to be read or written;

wherein, for each of a plurality of databases within which the one or more database servers perform database operations, the one or more storage devices store at least some data;

wherein the I/O requests are accompanied by request metadata that at least specifies to which databases of the plurality of databases the data involved in the I/O requests logically belong;

queuing, within the storage system, a plurality of the I/O requests;

when the storage system is ready to process a queued I/O request, a storage server within the storage system selecting which queued I/O request to process based on at least a first policy;

wherein the first policy distinguishes between I/O requests in part based on the databases to which the data involved in the I/O requests logically belong, as specified by the request metadata;

processing the queued I/O request that is selected based on the policy;

wherein the method is performed by one or more computing devices.

42. The one or more non-transitory computer-readable media of claim 41, wherein the instructions, when executed by the one or more computing devices, further cause the storage system receiving an instruction to change the first policy from the one or more database servers.

43. The one or more non-transitory computer-readable media of claim 41, wherein the first policy identifies at least a ratio of requests to process from a first set of one or more databases to requests to process from a second set of one or more databases.

44. The one or more non-transitory computer-readable media of claim 41, wherein the instructions, when executed by the one or more computing devices, further cause:

storing the first policy in association with a particular database;

receiving data indicating how to divide a set of I/O requests that access the particular database into a plurality of groups based on at least one logical characteristic of the I/O requests, wherein the first policy indicates to the storage server how to identify a group of the plurality of groups from which to select a next I/O request to process.

50. The one or more non-transitory computer-readable media of claim 41, wherein the instructions, when executed by the one or more computing devices, further cause:

receiving, at the one or more database servers, one or more database commands to manipulate or search for data objects in the plurality of databases;

at the database server, translating the one or more database commands into the I/O requests;

responsive to the I/O requests, receiving, at the database server, blocks of data from the storage system;

translating, at the database server, the blocks of data received from the storage system into the data objects, from the plurality of databases, referenced by the database commands;

executing, at the database server, the one or more database commands based on the data objects translated from the blocks of data received from the storage system.

45. One or more non-transitory computer-readable media storing instructions which, when executed by one or more computing devices, cause:

receiving, at a storage system, from a database server, input/output (I/O) requests to read data from or write data to one or more storage devices;

queuing, within the storage system, a plurality of the I/O requests;

grouping the plurality of I/O requests into one or more groups based on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

wherein grouping the plurality of I/O requests comprises grouping a first set of I/O requests in the plurality of I/O requests into a first group based on one or more logical characteristics specified by the database server when issuing the first set of I/O requests, the one or more logical characteristics including at least one of;

a database name associated with the first set of I/O requests, the database name specified by request metadata that accompanies the first I/O request;

a workload type, the workload type categorizing work, performed by the database server, for which the database server issued the first set of I/O requests;

a consumer group, comprising a plurality of consumers, associated with the first set of I/O requests;

a user name associated with a communication session responsive to which the database server issued the first set of I/O requests;

a service through which the database server issued the first set of I/O requests;

or

a purpose for which the database server issued the first set of I/O requests

receiving, at the storage system, one or more selection policies from the database server, the one or more selection policies specifying one or more ratios for the one or more groups;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on the one or more ratios and the group to which the particular I/O request belongs;

,

processing the particular I/O request in response to the storage server selecting the particular I/O request.

46. One or more non-transitory computer-readable media storing instructions which, when executed by one or more computing devices, cause:

receiving, at a storage system, from a database server, input/output (I/O) requests to read data from or write data to one or more storage devices;

queuing, within the storage system, a plurality of the I/O requests;

grouping the plurality of I/O requests into one or more groups based on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

receiving, at the storage system, one or more selection policies from the database server, the one or more selection policies specifying one or more ratios for the one or more groups;

receiving from the database server, with the one or more selection policies, policy-to-phase assignment data indicating how the one or more selection policies are to be applied over a plurality of phases, wherein the one or more selection policies include a plurality of policies;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on the one or more ratios and the group to which the particular I/O request belongs;

,

wherein selecting the particular I/O request comprises;

based at least on the policy-to-phase assignment data, identifying one or more first policies, of the one or more selection policies, to apply during one or more first phases of the plurality of phases;

during the one or more first phases, filtering the queued plurality of I/O requests by applying the identified one or more first policies, thereby yielding a filtered set of I/O requests;

based at least on the policy-to-phase assignment data, identifying a final policy, of the one or more selection policies, to apply during a final phase of the plurality of phases; and

during the final phase of the plurality of phases, based on the policy-to-phase assignment data, selecting a particular I/O request from the filtered set of I/O requests by applying the final policy;

processing the particular I/O request in response to the storage server selecting the particular I/O request.

47. The one or more non-transitory computer-readable media of claim 46, wherein the final policy involves a final ratio of the one or more ratios that is different than any ratio involved in the one or more first policies.

48. One or more non-transitory computer-readable media storing instructions which, when executed by one or more computing devices, cause:

receiving, at a storage system, from a database server, input/output (I/O) requests to read data from or write data to one or more storage devices;

queuing, within the storage system, a plurality of the I/O requests;

grouping the plurality of I/O requests into one or more groups based on one or more logical characteristics associated with particular I/O requests in the plurality of the I/O requests;

receiving, at the storage system, one or more selection policies from the database server, the one or more selection policies specifying one or more ratios for the one or more groups;

when the storage system is ready to process a pending I/O request that has been queued in the storage system, a storage server within the storage system selecting, from the queued plurality of the I/O requests, a particular I/O request to process based, at least in part, on the one or more ratios and the group to which the particular I/O request belongs;

,

wherein selecting the particular I/O request comprises;

based on the one or more ratios, identifying load usage allocations for a plurality of groups of I/O requests, the plurality of groups including the one or more groups;

based on load statistics, identifying actual load usages for the plurality of groups over a period of time;

identifying a particular group, of the one or more groups, whose actual load usage is further behind the load usage allocated to the particular group than any other group in the plurality of groups;

selecting the particular I/O request from the particular group;

processing the particular I/O request in response to the storage server selecting the particular I/O request.