# Patent

## Title
Enhancing data processing performance by cache management of fingerprint index

## Abstract

Various embodiments for improving hash index key lookup caching performance in a computing environment are provided. In one embodiment, for a cached fingerprint map having a plurality of entries corresponding to a plurality of data fingerprints, reference count information is used to determine a length of time to retain the plurality of entries in cache. Those of the plurality of entries having a higher reference counts are retained longer than those having lower reference counts.

## Background
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a Continuation of U.S. patent application Ser. No. 13/801,472, filed on Mar. 13, 2013, which is a Continuation of U.S. patent application Ser. No. 13/465,456, filed on May 7, 2012.


FIELD OF THE INVENTION
The present invention relates in general to computers, and more particularly to a method, system, and computer program product for enhancing data processing performance in computing storage environments.
DESCRIPTION OF THE RELATED ART
Computers and computer systems are found in a variety of settings in today's society. Computing environments and networks may be found at home, at work, at school, in government, and in other settings. Computing environments increasingly store data in one or more storage environments, which in many cases are remote from the local interface presented to a user.
These computing storage environments may use many storage devices such as disk drives, often working in concert, to store, retrieve, and update a large body of data, which may then be provided to a host computer requesting or sending the data. In some cases, a number of data storage subsystems are collectively managed as a single data storage system. These subsystems may be managed by host “sysplex” (system complex) configurations that combine several processing units or clusters of processing units. In this way, multi-tiered/multi-system computing environments, often including a variety of types of storage devices, may be used to organize and process large quantities of data.
SUMMARY OF THE INVENTION
Many multi-tiered/multi-system computing environments implement data deduplication technologies to improve storage performance by reducing the amount of duplicated storage across storage devices. Data deduplication systems are increasingly utilized because they help reduce the total amount of physical storage that is required to store data. This reduction is accomplished by ensuring that duplicate data is not stored multiple times. Instead, for example, if a chunk of data matches with an already stored chunk of data, a pointer to the original data is stored in the virtual storage map instead of allocating new physical storage space for the new chunk of data. Thus each chunk of data in a data deduplication system is associated with a “reference counter” that indicates how many virtual map elements are pointing to a given chunk of data.
Such data deduplication systems must grapple with the problem of being able to store large amounts of mapping information that map virtual storage space to physical disk storage space, for example, or so-called “fingerprints” of data chunks that map to already stored blocks of data. This situation is at least partly due to the fact that unlike traditional Redundant Array of Independent Disks (RAID) systems where virtual-to-physical mappings are determined algorithmically, data deduplication maps may point to any random chunk of physical disk storage. When inline data deduplication is used, it is generally impractical or impossible to store the complete map in memory because of its size. Accordingly, only portions of the map are cached depending on access pattern. As a result, the correct caching and retrieval of the most relevant parts of these storage maps at a particular time become increasingly important.
Inline data deduplication systems must maintain the aforementioned storage mapping information (including reference counter information) in-memory for fast access to data. Otherwise, an additional map fault penalty is incurred when fetching mapping information from physical storage, which thereby significantly increases storage latency. Hence, the storage controller must be able to identify those parts of the deduplication map that must be cached in-memory at a particular time. In contrast, conventional caching algorithms are based on traditional “locality of reference” models to cache virtualization maps. A need exists for a more effective way of cache management for such storage maps, and in particular for purposes of the present invention, the fingerprint index, or map.
In view of the forgoing need to better manage the caching of such fingerprint mapping information, various embodiments for improving hash index key lookup caching performance in a computing environment by a processor are provided. In one embodiment, by way of example only, for a cached fingerprint map having a plurality of entries corresponding to a plurality of data fingerprints, reference count information is used to determine the length of time to retain the plurality of entries in cache. Those of the plurality of entries having a higher reference counts are retained longer than those having lower reference counts.
In one embodiment, by way of example only, for a cached fingerprint map having a plurality of entries corresponding to a plurality of data fingerprints, reference count information obtained from a data deduplication engine is used to determine a length of time to retain the plurality of entries of the fingerprint map in cache, by: 1) examining the reference count information of the plurality of entries of the fingerprint map in the cache and a storage policy related to the plurality of entries to establish a retention duration for the plurality of entries, and 2) querying whether the reference count information for a data segment has been incremented, the incremented reference count information indicating a frequency of times the data segment has been accessed, or whether a predetermined time interval has expired. If the reference count information for a data segment has not been incremented or if the predetermined time interval has not expired, reiterating the step of querying. If the reference count information for a data segment has been incremented or if the predetermined time interval has expired in which no physical activity has been observed on a physical block, re-determining a new appropriate duration of retention in the cache.
In addition to the foregoing exemplary embodiment, various additional embodiments are provided and supply related advantages.



BRIEF DESCRIPTION OF THE DRAWINGS
In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which:
FIG. 1 is a block diagram illustrating an exemplary computing environment which may implement aspects of the present invention;
FIG. 2 is a block diagram showing a hardware structure of a data storage system, again in which aspects of the present invention may be implemented;
FIG. 3A is a block diagram of a cache system embodiment of the present invention illustrating a relationship between data deduplication system, data frequency index map and cache management module for improving caching performance;
FIG. 3B is a block diagram of a cache system embodiment of the present invention illustrating a relationship between cache management module and fingerprint cache for improving caching performance;
FIG. 4 is a flow chart diagram of an exemplary embodiment for enhancing data caching performance in which aspects of the present invention may be implemented;
FIG. 5 is a flow chart diagram of an additional exemplary embodiment for enhancing data caching performance, again in which aspects of the present invention may be implemented; and
FIG. 6 is a flow chart diagram of an exemplary embodiment for cache management of data segments, again in which aspects of the present invention may be implemented.



DETAILED DESCRIPTION OF THE DRAWINGS
As one of ordinary skill in the art will appreciate, as computing storage environments grow, so does the limitation on the ability for any whole storage mapping of associated data segments to be cached in memory for quick access. This limitation becomes more pronounced when inline data deduplication systems are implemented, as again as previously described, it is difficult or impossible to store a complete storage mapping in cache memory due to its size. As a result, only portions of the storage mapping are cached at any particular time.
To address and improve upon the current state of the art, the illustrated embodiments describe mechanisms to utilize so-called “reference count” information of various data segments as provided by the deduplication system (e.g., deduplication engine) to enhance a fingerprint map caching algorithm to better identify parts of the fingerprint storage mapping information that must be cached in-memory to ensure faster inline data access, and thereby, improve the caching performance of the storage environment.
Storage systems that incorporate data deduplication functionality implement a reference count for each segment of data, which indicates, for example, how many segments of virtual storage map onto a single segment of physical storage. Reference count information is generally readily available, as such reference count functionality is found in most, if not all, inline data deduplication systems. By improving caching performance of fingerprint storage mapping information, the average latency of input/output (I/O) operations in inline data deduplication systems may be significantly reduced.
In the following description, reference is made to the accompanying drawings which form a part hereof and which illustrate several embodiments of the present invention. It is understood that other embodiments may be utilized and structural and operational changes may be made without departing from the scope of the present invention.
Turning to FIG. 1, an example computer system 10 is depicted in which aspects of the present invention may be realized. Computer system 10 includes central processing unit (CPU) 12, which is connected to mass storage device(s) 14 and memory device 16. Mass storage devices may include hard disk drive (HDD) devices, which may be configured in a redundant array of independent disks (RAID). The cache management operations further described may be executed on device(s) 14, located in system 10 or elsewhere. Memory device 16 may include such memory as electrically erasable programmable read only memory (EEPROM) or a host of related devices. Memory device 16 and mass storage device 14 are connected to CPU 12 via a signal-bearing medium. In addition, CPU 12 is connected through communication port 18 to a communication network 20, having an attached plurality of additional computer systems 22 and 24. The computer system 10 may include one or more processor devices (e.g., CPU 12) and additional memory devices 16 for each individual component of the computer system 10 to execute and perform each operation described herein to accomplish the purposes of the present invention.
FIG. 2 is an exemplary block diagram 200 showing a hardware structure of a data storage system in a computer system according to the present invention. Host computers 210, 220, 225, are shown, each acting as a central processing unit for performing data processing as part of a data storage system 200. The hosts (physical or virtual devices), 210, 220, and 225 may be one or more new physical devices or logical devices to accomplish the purposes of the present invention in the data storage system 200. In one embodiment, by way of example only, a data storage system 200 may be implemented as IBM® System StorageTM DS8000TM. A Network connection 260 may be a fibre channel fabric, a fibre channel point to point link, a fibre channel over ethernet fabric or point to point link, a FICON or ESCON I/O interface, any other I/O interface type, a wireless network, a wired network, a LAN, a WAN, heterogeneous, homogeneous, public (i.e. the Internet), private, or any combination thereof. The hosts, 210, 220, and 225 may be local or distributed among one or more locations and may be equipped with any type of fabric (or fabric channel) (not shown in FIG. 2) or network adapter 260 to the storage controller 240, such as Fibre channel, FICON, ESCON, Ethernet, fiber optic, wireless, or coaxial adapters. Data storage system 200 is accordingly equipped with a suitable fabric (not shown in FIG. 2) or network adapter 260 to communicate. Data storage system 200 is depicted in FIG. 2 comprising storage controller 240 and storage 230.
To facilitate a clearer understanding of the methods described herein, storage controller 240 is shown in FIG. 2 as a single processing unit, including a microprocessor 242, system memory 243 and nonvolatile storage (“NVS”) 216, which will be described in more detail below. It is noted that in some embodiments, storage controller 240 is comprised of multiple processing units, each with their own processor complex and system memory, and interconnected by a dedicated network within data storage system 200. Storage 230 may be comprised of one or more storage devices, such as storage arrays, which are connected to storage controller 240 by a storage network.
In some embodiments, the devices included in storage 230 may be connected in a loop architecture. Storage controller 240 manages storage 230 and facilitates the processing of write and read requests intended for storage 230. The system memory 243 of storage controller 240 stores program instructions and data that the processor 242 may access for executing functions associated with managing storage 230. In one embodiment, system memory 243 includes, is associated, or is in communication with the operation software 250, and configured in part for accomplishing functionality of the present invention. As shown in FIG. 2, system memory 243 may also include or be in communication with a data cache 245 for storage 230, also referred to herein as a “cache memory”, for buffering “write data” and “read data”, which respectively refer to write/read requests and their associated data. In one embodiment, data cache 245 is allocated in a device external to system memory 243, yet remains accessible by microprocessor 242 and may serve to provide additional security against data loss, in addition to carrying out the operations as described in herein.
In some embodiments, data cache 245 is implemented with a volatile memory and non-volatile memory and coupled to microprocessor 242 via a local bus (not shown in FIG. 2) for enhanced performance of data storage system 200. The NVS 216 included in data storage controller is accessible by microprocessor 242 and serves to provide additional support for operations and execution of the present invention as described in other figures. The NVS 216, may also referred to as a “persistent” cache, or “cache memory” and is implemented with nonvolatile memory that may or may not utilize external power to retain data stored therein. The NVS may be stored in and with the data cache 245 for any purposes suited to accomplish the objectives of the present invention. In some embodiments, a backup power source (not shown in FIG. 2), such as a battery, supplies NVS 216 with sufficient power to retain the data stored therein in case of power loss to data storage system 200. In certain embodiments, the capacity of NVS 216 is less than or equal to the total capacity of data cache 245.
Storage 230 may be physically comprised of one or more storage devices, such as storage arrays. A storage array is a logical grouping of individual storage devices, such as a hard disk. In certain embodiments, storage 230 is comprised of a JBOD (Just a Bunch of Disks) array or a RAID (Redundant Array of Independent Disks) array. A collection of physical storage arrays may be further combined to form a rank, which dissociates the physical storage from the logical configuration. The storage space in a rank may be allocated into logical volumes, which define the storage location specified in a write/read request.
In one embodiment the storage system as shown in FIG. 2 may include a logical volume, or simply “volume,” with corresponding varying kinds of allocations. Storage 230a, 230b and 230n are shown as ranks in data storage system 200, and are referred to herein as rank 230a, 230b and 230n. Ranks may be local to data storage system 200, or may be located at a physically remote location. In other words, a local storage controller may connect with a remote storage controller and manage storage at the remote location. Rank 230a is shown configured with two entire volumes, 234 and 236, as well as one partial volume 232a. Rank 230b is shown with another partial volume 232b. Thus volume 232 is allocated across ranks 230a and 230b. Rank 230n is shown as being fully allocated to volume 238—that is, rank 230n refers to the entire physical storage for volume 238. From the above examples, it will be appreciated that a rank may be configured to include one or more partial and/or entire volumes. Volumes and ranks may further be divided into so-called “tracks,” which represent a fixed block of storage. A track is therefore associated with a given volume and may be given a given rank.
The storage controller 240 may include a data deduplication engine 255, cache management module 257, block map 259, fingerprint map 261, and fingerprint cache 263 as will be further described. The cache management module 257 may work in conjunction with each and every component of the storage controller 240, the hosts 210, 220, 225, and storage devices 230. The cache management module 257 may be, as one of ordinary skill in the art will appreciate, structurally one complete module or may be associated and/or included with other individual modules. The cache management module 257 may also be located in the data cache 245 or other components.
The storage controller 240 includes a control switch 241 for controlling the fiber channel protocol to the host computers 210, 220, 225, a microprocessor 242 for controlling all the storage controller 240, a nonvolatile control memory 243 for storing a microprogram (operation software) 250 for controlling the operation of storage controller 240, data for control and each table described later, data cache 245 for temporarily storing (buffering) data, and buffers 244 for assisting the data cache 245 to read and write data, a control switch 241 for controlling a protocol to control data transfer to or from the storage devices 230. Multiple buffers 244 may be implemented with the present invention to assist with the operations as described herein.
The storage controller 240 is shown including a data deduplication engine 255, storage map/data frequency index map (DFIM) 259 (“storage map” 259), and cache management module 257. The data deduplication engine 255, cache management module 257 and DFIM 259 may operate in conjunction with each and every component of the storage controller 240, the hosts, 210, 220, 225, and storage devices 230, to accomplish functionality according to the present invention. The data deduplication engine 255, cache management module 257 and DFIM 259 may be structurally one complete module or may be associated and/or incorporated within other individual modules. The cache management module 257 and DFIM 259 may also be incorporated in the cache 245 or other components.
Data deduplication engine 255 is configured for performing, in conjunction with other components of storage controller 240 such as microprocessor 242, data deduplication operations on write data passed through storage controller 240 to storage 230.
As previously indicated, storage controller 240 includes a data frequency block map 259 for short. Data cache 245 (or what may be termed holistically as cache system 245 (which may incorporate cache management module 257, block map 259, or even data deduplication engine 255) accepts write data from hosts 210, 220, and 225, or similar devices, that is then placed in cache memory 245. Data deduplication engine 255 then tests the write data for duplication in the cache memory 245 and writes an index and frequency for such in the block map 259. In conjunction with block map 259, the data deduplication engine generates fingerprint information corresponding to stored blocks of data, writing an index for such in the fingerprint map 261. Fingerprints of new blocks of data are then compared with the indexed fingerprints in the fingerprint map to determine if exact replicas of data are found.
Fingerprint map 261 may be partially or wholly temporarily stored in fingerprint cache 263. In one embodiment, the size of fingerprint map 261 is such (due to the immense underlying storage 230 and data processing occurring in relation to such storage 230) that only a portion of the fingerprint map 261 may be stored “in-memory” (cached) in the fingerprint cache 263 at any one time.
Turning now to FIG. 3A, a block diagram of various functional aspects 300 of the present invention are depicted as an exemplary flow, specifically the creation of reference count information to be later used in cache management by the cache management module 260. Specifically, data cache system 245 is shown to accept write data 302 to be processed through data deduplication engine 255 as a write operation 304 to data cache 245. As the write data 302 is processed through the data deduplication engine 255, and as previously described, the write data 302 is tested for duplication with existing storage, and the deduplication engine 255 passes the frequency and index information 306 to the data frequency index/block map 259. Storage systems that incorporate data deduplication functionality as shown in FIG. 3, include a reference count for each chunk of data, which indicates how many chunks of virtual storage map onto a single chunk of physical storage, among other indications.
As data is read 312 out of the cache 245, the block map 259 is updated. The information contained in block map 259 is provided, including reference count information 310, to the cache management module 260, which is also in bi-directional communication 314 between the data cache 245 and the storage controller 240 (FIG. 2), and thereby hosts 210, 220, and 225 as read data 312.
Turning now to FIG. 3B, a block diagram of various function aspects 320 of the present invention are depicted as an additional exemplary flow, specifically the use of reference count information 310 as previously described to perform cache management information to the fingerprint map 261. Based at least in part on the activities previously described in FIG. 3A, the cache management module 260 may determine which of portions of the fingerprint map 261 to be placed in the fingerprint cache 263 and for what appropriate length of time as will be further illustrated, according to aspects of the present invention.
As previously described, reference count information 310 is used by the cache management module 260 to determine which portions of the fingerprint map 261 will be retained in the fingerprint cache 263. A write command may be processed by the data deduplication engine 255 (e.g., FIG. 3A) to obtain/generate a fingerprint representative of the write data to be written to storage. The fingerprint information 322 is then provided to the cache management module 260 as shown, which calls up the cached portion of the fingerprint map 261 from the fingerprint cache 263 (via bilateral communication 316) to determine if an exact match is found. This result is provided as fingerprint data 318 to the data deduplication engine 255. If an exact match is found, the reference count for such data may be updated, but the data is not rewritten to physical storage. In one embodiment, based at least in part on use of the reference count information to determine which portions of the fingerprint map are cached in-memory, the likelihood of the relevant portion of the fingerprint map 261 corresponding to the incoming fingerprint information 322 is increased, and alleviates a further need to call up additional portions of the fingerprint map 261 from storage according to mechanisms further described.
Turning now to FIG. 4, a flow chart diagram of a method for improving caching performance in a storage environment is shown in one exemplary embodiment. Method 400 begins (step 402) by using the aforementioned reference count information to determine an appropriate length of time to retain particular entries (e.g., portions) of the aforementioned fingerprint map 261 (e.g., FIG. 3B) in the fingerprint cache 263 (step 404). The method 400 ends (step 406).
FIG. 5, following, is a flow chart diagram of a method for implementing such utilization of reference count information, as shown previously in FIG. 4, in a further exemplary embodiment. Here, method 500 begins (step 502) by examining reference count data obtained from the deduplication engine in the course of a deduplication operation as previously described (step 504). Based on the reference count information (and/or by implementation of a particular storage policy), a retention duration for a particular entry in the fingerprint map, or for a number of entries in the fingerprint map, is established (step 506).
Continuing with FIG. 5, the method 500 then queries if the reference count information for the referenced data segment has been updated (e.g., incremented pursuant to a deduplication operation), or whether, for example, a predetermined time interval has expired (step 508) in which no activity is observed on the physical block. If this is the case, the retention duration that was previously established in step 506 is revisited to re-determine a new appropriate duration of retention in the cache (step 510). Returning to step 508, if the reference count information is not updated, or the predetermined time interval is not expired, the method 500 returns to step 508 with the passage of time to again query whether either or both of these conditions has been satisfied.
The methodologies described in FIGS. 4 and 5, previously may incorporate certain weighting factors into consideration, such as a predetermined weight that diminishes over time such that even data segments having high reference counts that see little or no activity will see their associated weights (and thereby the importance of the fingerprint information for the referenced data segment to be retained in the cache) slowly decreased. As one of ordinary skill in the art will appreciate, these weighting factors may be utilized in various ways with or without other considerations so as to effectively address the relative importance of fingerprint information of referenced data segments over the passage of time, use, resource utilization (such as bandwidth and other scarce system resources), and the like in order to suit a particular application.
As one of ordinary skill in the art will appreciate, a wide variety of storage policies (which may, for example, be established with the assistance of a administrator/user) may be brought to bear on whether a particular entry or set of entries (i.e., portions) in the fingerprint map should be retained for a certain duration, based on the current reference count information for that entry or set of entries. Since reference count information indicates, for a given segment of data, the likelihood of a particular entry being accessed, this same information may be intelligently used by such policies or otherwise in map caching mechanisms (such as a map caching algorithm that may be implemented by the cache management module previously described) in order to determine those candidate entries stored in the fingerprint map that should be paged out from cache memory.
In view of the foregoing, consider the following example. Ten (10) mapping table entries are established as candidates for being paged out. Of those ten mapping table entries, those that contain higher reference counts (for all data segments together, in one embodiment) will be paged out later than those that have a lower reference count. In this manner, fingerprint map portions having corresponding higher reference counts are retained longer, with the expectation that they will be reused again, and when this occurs, the particular entry will be found in cache for fast access.
FIG. 6, following, illustrates a flow chart diagram of an exemplary method for retention of mapping table entries in cache using reference count values, in which aspects of the present invention may be implemented. Method 600 begins (step 602) with a query as to whether the cache is full, and whether despite this fact new map entries are to be fetched from disk (thereby requiring other map entries to be paged out) (step 604). If this is the case, the fingerprint map entries are collectively examined to determine which of those entries to page out from cache (step 606). As part of this examination process, method 600 then queries if a particular examined entry has a reference count value that is high (for example, in one embodiment, above a particular threshold set by policy) (step 608). If this is the case, the entry is retained in cache (step 610). If the entry is determined not to have a high value, the entry is designated to be paged out from cache (step 612) and a new map entry may be paged into cache in its place.
As will be appreciated by one of ordinary skill in the art, aspects of the present invention may be embodied as a system, method or computer program product. Accordingly, aspects of the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “circuit,” “module,” “process” or “system.” Furthermore, aspects of the present invention may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.
Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device.
Program code embodied on a computer readable medium may be transmitted using any appropriate medium, including but not limited to wireless, wired, optical fiber cable, RF, etc., or any suitable combination of the foregoing. Computer program code for carrying out operations for aspects of the present invention may be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Smalltalk, C++ or the like and conventional procedural programming languages, such as the “C” programming language or similar programming languages. The program code may execute entirely on the user's computer, partly on the user's computer, or entirely on the remote computer or server. In the last scenario, the remote computer may be connected to the user's computer through any type of network, including a local area network (LAN) or a wide area network (WAN), or the connection may be made to an external computer (for example, through the Internet using an Internet Service Provider).
Aspects of the present invention are described below with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer readable medium that can direct a computer, other programmable data processing apparatus, or other devices to function in a particular manner, such that the instructions stored in the computer readable medium produce an article of manufacture including instructions which implement the function/act specified in the flowchart and/or block diagram block or blocks. The computer program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other devices to cause a series of operational steps to be performed on the computer, other programmable apparatus or other devices to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide processes for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.
The flowchart and block diagrams in the above figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present invention. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions.
While one or more embodiments of the present invention have been illustrated in detail, one of ordinary skill in the art will appreciate that modifications and adaptations to those embodiments may be made without departing from the scope of the present invention as set forth in the following claims.

## Claims

1. A method for improving hash index key lookup caching performance in a computing environment by a processor, comprising:
for a cached fingerprint map having a plurality of entries corresponding to a plurality of data fingerprints used by a data deduplication system, using reference count information obtained from a data deduplication engine to determine a length of time to retain the plurality of entries of the fingerprint map in cache, by:
examining the reference count information of the plurality of entries of the fingerprint map in the cache and a storage policy related to the plurality of entries to establish a retention duration for the plurality of entries, and
querying whether the reference count information for a data segment has been incremented, the incremented reference count information indicating a frequency of times the data segment has been accessed, or whether a predetermined time interval has expired;

if the reference count information for a data segment has not been incremented or if the predetermined time interval has not expired, reiterating the step of querying; and
if the reference count information for a data segment has been incremented or if the predetermined time interval has expired in which no physical activity has been observed on a physical block, re-determining a new appropriate duration of retention in the cache.

2. The method of claim 1, further including obtaining the reference count information from a data deduplication engine.

3. The method of claim 1, further including, when the cache is full, retaining in the cache the plurality of entries of the fingerprint map having higher reference counts and removing from the cache the plurality of entries of the fingerprint map having lower reference counts.

4. The method of claim 1, further including performing the re-determining for every reference count increment.

5. The method of claim 1, wherein determining the length of time to retain the plurality of entries in cache includes implementing at least one policy corresponding to one of the length of time or at least one of the plurality of entries.

6. The method of claim 1, wherein the determining the length of time to retain the plurality of entries in cache is performed in approximate synchronization with a deduplication operation for those of the plurality of entries retained in the cache.

7. The method of claim 1, further comprising assigning a predetermined weight to the data segment that diminishes over time as physical activity observed on a physical block decreases.