Patent Publication Number: US-9407523-B2

Title: Increasing performance of a streaming application by running experimental permutations

Description:
BACKGROUND 
     1. Technical Field 
     This disclosure generally relates to streaming applications, and more specifically relates to enhancing performance of a streaming application by running experimental permutations. 
     2. Background Art 
     Streaming applications are known in the art, and typically include multiple operators coupled together in a flow graph that process streaming data in near real-time. An operator typically takes in streaming data in the form of data tuples, operates on the tuples in some fashion, and outputs the processed tuples to the next operator. Streaming applications are becoming more common due to the high performance that can be achieved from near real-time processing of streaming data. 
     Many streaming applications require significant computer resources, such as processors and memory, to provide the desired near real-time processing of data. However, the workload of a streaming application can vary greatly over time. Allocating on a permanent basis computer resources to a streaming application that would assure the streaming application would always function as desired (i.e., during peak demand) would mean many of those resources would sit idle when the streaming application is processing a workload significantly less than its maximum. Furthermore, what constitutes peak demand at one point in time can be exceeded as the usage of the streaming application increases. For a dedicated system that runs a streaming application, an increase in demand may require a corresponding increase in hardware resources to meet that demand. 
     BRIEF SUMMARY 
     A streams manager monitors performance of a streaming application, and when the performance needs to be improved, the streams manager automatically requests virtual machines from a cloud manager. In response, the cloud manager provisions one or more virtual machines in a cloud. The streams manager builds a permutation of a flow graph for the streaming application using the virtual machine(s), runs the permutation in parallel with the corresponding portion of the flow graph, and compares the performance of the original portion of the flow graph to the performance of the permutation. When the performance of the permutation exceeds the performance of the original part of the flow graph, the streams manager modifies the flow graph so the permutation replaces the original part of the flow graph. In this manner a streaming application can dynamically evolve to increase its performance as needed. 
     The foregoing and other features and advantages will be apparent from the following more particular description, as illustrated in the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       The disclosure will be described in conjunction with the appended drawings, where like designations denote like elements, and: 
         FIG. 1  is a block diagram of a cloud computing node; 
         FIG. 2  is a block diagram of a cloud computing environment; 
         FIG. 3  is a block diagram of abstraction model layers; 
         FIG. 4  is a block diagram showing some features of a cloud manager; 
         FIG. 5  is a block diagram showing some features of a streams manager; 
         FIG. 6  is a flow diagram of a method for a streams manager to request and receive from a cloud manager virtual machines to improve performance of a streaming application; 
         FIG. 7  is a flow diagram of a method for a streams manager to automatically generate a permutation of a flow graph and modify the flow graph when performance of the permutation exceeds performance of the corresponding original portion of the flow graph; 
         FIG. 8  is a block diagram of one specific example of a streaming application; 
         FIG. 9  is a block diagram showing examples of permutations types; 
         FIG. 10  is a block diagram showing the original flow graph with a permutation of the flow graph that reorders two operators; 
         FIG. 11  is a block diagram showing replacement of the original operators A, B, C and D in the flow graph with the permutation shown in  FIG. 10 ; 
         FIG. 12  is a block diagram showing the original flow graph with a permutation of the flow graph that splits two operators; 
         FIG. 13  is a block diagram showing replacement of the original operators A, B, C and D in the flow graph with the permutation shown in  FIG. 12 ; 
         FIG. 14  is a block diagram showing the original flow graph with a permutation of the flow graph that coalesces two operators; and 
         FIG. 15  is a block diagram showing replacement of the original operators A, B, C and D in the flow graph with the permutation shown in  FIG. 14 . 
     
    
    
     DETAILED DESCRIPTION 
     The disclosure and claims herein relate to a streams manager that monitors performance of a streaming application, and when the performance needs to be improved, the streams manager automatically requests virtual machines from a cloud manager. In response, the cloud manager provisions one or more virtual machines in a cloud. The streams manager builds a permutation of a flow graph for the streaming application using the virtual machine(s), runs the permutation in parallel with the corresponding portion of the flow graph, and compares the performance of the original portion of the flow graph to the performance of the permutation. When the performance of the permutation exceeds the performance of the original part of the flow graph, the streams manager modifies the flow graph so the permutation replaces the original part of the flow graph. In this manner a streaming application can dynamically evolve to increase its performance as needed. 
     It is understood in advance that although this disclosure includes a detailed description on cloud computing, implementation of the teachings recited herein are not limited to a cloud computing environment. Rather, embodiments of the present invention are capable of being implemented in conjunction with any other type of computing environment now known or later developed. 
     Cloud computing is a model of service delivery for enabling convenient, on-demand network access to a shared pool of configurable computing resources (e.g., networks, network bandwidth, servers, processing, memory, storage, applications, virtual machines, and services) that can be rapidly provisioned and released with minimal management effort or interaction with a provider of the service. This cloud model may include at least five characteristics, at least three service models, and at least four deployment models. 
     Characteristics are as follows: 
     On-demand self-service: a cloud consumer can unilaterally provision computing capabilities, such as server time and network storage, as needed automatically without requiring human interaction with the service&#39;s provider. 
     Broad network access: capabilities are available over a network and accessed through standard mechanisms that promote use by heterogeneous thin or thick client platforms (e.g., mobile phones, laptops, and PDAs). 
     Resource pooling: the provider&#39;s computing resources are pooled to serve multiple consumers using a multi-tenant model, with different physical and virtual resources dynamically assigned and reassigned according to demand. There is a sense of location independence in that the consumer generally has no control or knowledge over the exact location of the provided resources but may be able to specify location at a higher level of abstraction (e.g., country, state, or datacenter). 
     Rapid elasticity: capabilities can be rapidly and elastically provisioned, in some cases automatically, to quickly scale out and rapidly released to quickly scale in. To the consumer, the capabilities available for provisioning often appear to be unlimited and can be purchased in any quantity at any time. 
     Measured service: cloud systems automatically control and optimize resource use by leveraging a metering capability at some level of abstraction appropriate to the type of service (e.g., storage, processing, bandwidth, and active user accounts). Resource usage can be monitored, controlled, and reported providing transparency for both the provider and consumer of the utilized service. 
     Service Models are as follows: 
     Software as a Service (SaaS): the capability provided to the consumer is to use the provider&#39;s applications running on a cloud infrastructure. The applications are accessible from various client devices through a thin client interface such as a web browser (e.g., web-based e-mail). The consumer does not manage or control the underlying cloud infrastructure including network, servers, operating systems, storage, or even individual application capabilities, with the possible exception of limited user-specific application configuration settings. 
     Platform as a Service (PaaS): the capability provided to the consumer is to deploy onto the cloud infrastructure consumer-created or acquired applications created using programming languages and tools supported by the provider. The consumer does not manage or control the underlying cloud infrastructure including networks, servers, operating systems, or storage, but has control over the deployed applications and possibly application hosting environment configurations. 
     Infrastructure as a Service (IaaS): the capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, deployed applications, and possibly limited control of select networking components (e.g., host firewalls). 
     Deployment Models are as follows: 
     Private cloud: the cloud infrastructure is operated solely for an organization. It may be managed by the organization or a third party and may exist on-premises or off-premises. 
     Community cloud: the cloud infrastructure is shared by several organizations and supports a specific community that has shared concerns (e.g., mission, security requirements, policy, and compliance considerations). It may be managed by the organizations or a third party and may exist on-premises or off-premises. 
     Public cloud: the cloud infrastructure is made available to the general public or a large industry group and is owned by an organization selling cloud services. 
     Hybrid cloud: the cloud infrastructure is a composition of two or more clouds (private, community, or public) that remain unique entities but are bound together by standardized or proprietary technology that enables data and application portability (e.g., cloud bursting for loadbalancing between clouds). 
     A cloud computing environment is service oriented with a focus on statelessness, low coupling, modularity, and semantic interoperability. At the heart of cloud computing is an infrastructure comprising a network of interconnected nodes. 
     Referring now to  FIG. 1 , a block diagram of an example of a cloud computing node is shown. Cloud computing node  100  is only one example of a suitable cloud computing node and is not intended to suggest any limitation as to the scope of use or functionality of embodiments of the invention described herein. Regardless, cloud computing node  100  is capable of being implemented and/or performing any of the functionality set forth hereinabove. 
     In cloud computing node  100  there is a computer system/server  110 , which is operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well-known computing systems, environments, and/or configurations that may be suitable for use with computer system/server  110  include, but are not limited to, personal computer systems, server computer systems, tablet computer systems, thin clients, thick clients, handheld or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments that include any of the above systems or devices, and the like. 
     Computer system/server  110  may be described in the general context of computer system executable instructions, such as program modules, being executed by a computer system. Generally, program modules may include routines, programs, objects, components, logic, data structures, and so on that perform particular tasks or implement particular abstract data types. Computer system/server  110  may be practiced in distributed cloud computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed cloud computing environment, program modules may be located in both local and remote computer system storage media including memory storage devices. 
     As shown in  FIG. 1 , computer system/server  110  in cloud computing node  100  is shown in the form of a general-purpose computing device. The components of computer system/server  110  may include, but are not limited to, one or more processors or processing units  120 , a system memory  130 , and a bus  122  that couples various system components including system memory  130  to processing unit  120 . 
     Bus  122  represents one or more of any of several types of bus structures, including a memory bus or memory controller, a peripheral bus, an accelerated graphics port, and a processor or local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, and Peripheral Component Interconnect (PCI) bus. 
     Computer system/server  110  typically includes a variety of computer system readable media. Such media may be any available media that is accessible by computer system/server  110 , and it includes both volatile and non-volatile media, removable and non-removable media. An example of removable media is shown in  FIG. 1  to include a Digital Video Disc (DVD)  192 . 
     System memory  130  can include computer system readable media in the form of volatile or non-volatile memory, such as firmware  132 . Firmware  132  provides an interface to the hardware of computer system/server  110 . System memory  130  can also include computer system readable media in the form of volatile memory, such as random access memory (RAM)  134  and/or cache memory  136 . Computer system/server  110  may further include other removable/non-removable, volatile/non-volatile computer system storage media. By way of example only, storage system  140  can be provided for reading from and writing to a non-removable, non-volatile magnetic media (not shown and typically called a “hard drive”). Although not shown, a magnetic disk drive for reading from and writing to a removable, non-volatile magnetic disk (e.g., a “floppy disk”), and an optical disk drive for reading from or writing to a removable, non-volatile optical disk such as a CD-ROM, DVD-ROM or other optical media can be provided. In such instances, each can be connected to bus  122  by one or more data media interfaces. As will be further depicted and described below, memory  130  may include at least one program product having a set (e.g., at least one) of program modules that are configured to carry out the functions described in more detail below. 
     Program/utility  150 , having a set (at least one) of program modules  152 , may be stored in memory  130  by way of example, and not limitation, as well as an operating system, one or more application programs, other program modules, and program data. Each of the operating system, one or more application programs, other program modules, and program data or some combination thereof, may include an implementation of a networking environment. Program modules  152  generally carry out the functions and/or methodologies of embodiments of the invention as described herein. 
     Computer system/server  110  may also communicate with one or more external devices  190  such as a keyboard, a pointing device, a display  180 , a disk drive, etc.; one or more devices that enable a user to interact with computer system/server  110 ; and/or any devices (e.g., network card, modem, etc.) that enable computer system/server  110  to communicate with one or more other computing devices. Such communication can occur via Input/Output (I/O) interfaces  170 . Still yet, computer system/server  110  can communicate with one or more networks such as a local area network (LAN), a general wide area network (WAN), and/or a public network (e.g., the Internet) via network adapter  160 . As depicted, network adapter  160  communicates with the other components of computer system/server  110  via bus  122 . It should be understood that although not shown, other hardware and/or software components could be used in conjunction with computer system/server  110 . Examples, include, but are not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, Redundant Array of Independent Disk (RAID) systems, tape drives, data archival storage systems, etc. 
     Referring now to  FIG. 2 , illustrative cloud computing environment  200  is depicted. As shown, cloud computing environment  200  comprises one or more cloud computing nodes  100  with which local computing devices used by cloud consumers, such as, for example, personal digital assistant (PDA) or cellular telephone  210 A, desktop computer  210 B, laptop computer  210 C, and/or automobile computer system  210 N may communicate. Nodes  100  may communicate with one another. They may be grouped (not shown) physically or virtually, in one or more networks, such as Private, Community, Public, or Hybrid clouds as described hereinabove, or a combination thereof. This allows cloud computing environment  200  to offer infrastructure, platforms and/or software as services for which a cloud consumer does not need to maintain resources on a local computing device. It is understood that the types of computing devices  210 A-N shown in  FIG. 2  are intended to be illustrative only and that computing nodes  100  and cloud computing environment  200  can communicate with any type of computerized device over any type of network and/or network addressable connection (e.g., using a web browser). 
     Referring now to  FIG. 3 , a set of functional abstraction layers provided by cloud computing environment  200  in  FIG. 2  is shown. It should be understood in advance that the components, layers, and functions shown in  FIG. 3  are intended to be illustrative only and the disclosure and claims are not limited thereto. As depicted, the following layers and corresponding functions are provided. 
     Hardware and software layer  310  includes hardware and software components. Examples of hardware components include mainframes, in one example IBM System z systems; RISC (Reduced Instruction Set Computer) architecture based servers, in one example IBM System p systems; IBM System x systems; IBM BladeCenter systems; storage devices; networks and networking components. Examples of software components include network application server software, in one example IBM WebSphere® application server software; and database software, in one example IBM DB2® database software. IBM, System z, System p, System x, BladeCenter, WebSphere, and DB2 are trademarks of International Business Machines Corporation registered in many jurisdictions worldwide. 
     Virtualization layer  320  provides an abstraction layer from which the following examples of virtual entities may be provided: virtual servers; virtual storage; virtual networks, including virtual private networks; virtual applications and operating systems; and virtual clients. 
     In one example, management layer  330  may provide the functions described below. Resource provisioning provides dynamic procurement of computing resources and other resources that are utilized to perform tasks within the cloud computing environment. Metering and Pricing provide cost tracking as resources are utilized within the cloud computing environment, and billing or invoicing for consumption of these resources. In one example, these resources may comprise application software licenses. Security provides identity verification for cloud consumers and tasks, as well as protection for data and other resources. User portal provides access to the cloud computing environment for consumers and system administrators. Service level management provides cloud computing resource allocation and management such that required service levels are met. Service Level Agreement (SLA) planning and fulfillment provide pre-arrangement for, and procurement of, cloud computing resources for which a future requirement is anticipated in accordance with an SLA. A cloud manager  350  is representative of a cloud manager as described in more detail below. While the cloud manager  350  is shown in  FIG. 3  to reside in the management layer  330 , cloud manager  350  can span all of the levels shown in  FIG. 3 , as discussed below. 
     Workloads layer  340  provides examples of functionality for which the cloud computing environment may be utilized. Examples of workloads and functions which may be provided from this layer include: mapping and navigation; software development and lifecycle management; virtual classroom education delivery; data analytics processing; transaction processing; and a streams manager  360 , as discussed in more detail below. 
     As will be appreciated by one skilled in the art, aspects of this disclosure may be embodied as a system, method or computer program product. Accordingly, aspects 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” 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 non-transitory 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. 
     A computer readable signal medium may include a propagated data signal with computer readable program code embodied therein, for example, in baseband or as part of a carrier wave. Such a propagated signal may take any of a variety of forms, including, but not limited to, electro-magnetic, optical, or any suitable combination thereof. A computer readable signal medium may be any computer readable medium that is not a computer readable storage medium and that can communicate, propagate, or transport 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, wireline, 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&#39;s computer, partly on the user&#39;s computer, as a stand-alone software package, partly on the user&#39;s computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer may be connected to the user&#39;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. 
       FIG. 4  shows one suitable example of the cloud manager  350  shown in  FIG. 3 . The cloud manager  350  includes a cloud provisioning mechanism  410  that includes a resource request interface  420 . The resource request interface  420  allows a software entity, such as the streams manager  360 , to request virtual machines from the cloud manager  350  without human intervention. The cloud manager  350  also includes a user interface  430  that allows a user to interact with the cloud manager to perform any suitable function, including provisioning of VMs, destruction of VMs, performance analysis of the cloud, etc. The difference between the resource request interface  420  and the user interface  430  is a user must manually use the user interface  430  to perform functions specified by the user, while the resource request interface  420  may be used by a software entity to request provisioning of cloud resources by the cloud mechanism  350  without input from a human user. Of course, cloud manager  350  could include many other features and functions known in the art that are not shown in  FIG. 4 . 
       FIG. 5  shows one suitable example of the streams manager  360  shown in  FIG. 3 . The streams manager  360  is software that manages one or more streaming applications, including creating operators and data flow connections between operators in a flow graph that represents a streaming application. The streams manager  360  includes a performance monitor  510  with one or more performance thresholds  520 . Performance thresholds  520  can include static thresholds, such as percentage used of current capacity, and can also include any suitable heuristic for measuring performance of a streaming application as a whole or for measuring performance of one or more operators in a streaming application. Performance thresholds  520  may include different thresholds and metrics at the operator level, at the level of a group of operators, and/or at the level of the overall performance of the streaming application. The stream performance monitor  510  monitors performance of a streaming application, and when current performance compared to the one or more performance thresholds  520  indicates current performance needs to be improved, the stream performance monitor  510  communicates the need for resources to the cloud resource request mechanism  530 . The cloud resource request mechanism  530 , in response to the communication from the stream performance monitor, assembles a cloud resource request  540 , which can include information such as a number of VMs to provision  550 , stream infrastructure needed in each VM  560 , and a stream application portion  570  for each VM. Once the cloud resource request  530  is formulated, the streams manager  360  submits the cloud resource request  540  to a cloud manager, such as cloud manager  350  shown in  FIGS. 3 and 4 . 
     The cloud resource request can be formatted in any suitable way. A simple example will illustrate two suitable ways for formatting a cloud resource request. Let&#39;s assume the streams manager determines it needs two VMs, where both have common stream infrastructure, with a first of the VMs hosting operator A and the second of the VMs hosting operator B. The cloud resource request  540  in  FIG. 5  could specify two VMs at  550 , could specify the common stream infrastructure, such as an operating system and middleware, at  560 , and could specify operator A and operator B at  570 . In response, the cloud manager would provision two VMs with the common stream infrastructure, with the first of the VMs hosting operator A and the second of the VMs hosting operator B. In the alternative, the cloud resource request  540  could be formulated such that each VM is specified with its corresponding stream infrastructure and stream application portion. In this configuration, the cloud resource request would specify a first VM with the common stream infrastructure and operator A, and a second VM with the common stream infrastructure and operator B. 
     Referring to  FIG. 6 , a method  600  shows one suitable example for enhancing performance of a streaming application, and is preferably performed by the streams manager  360  interacting with the cloud manager  350 . The streams manager requests resources, such as VMs, from the cloud manager (step  610 ). The cloud manager provisions the VMs (step  620 ). The streams manager then deploys a portion of the flow graph to the VMs (step  630 ). When the streaming application is not initially hosted in the cloud, the result will be a hybrid implementation of the streams application, with some portions hosted on a dedicated computer system and other portions hosted by one or more VMs in the cloud. 
       FIG. 7  shows one suitable example of a method  700  for enhancing performance of a streaming application. The streams manager monitors performance of the flow graph (step  710 ). This can be done, for example, by comparing current performance to one or more performance thresholds. When performance does not need to be increased (step  720 =NO), method  700  loops back to step  710  and continues. When performance needs to be increased (step  720 =YES), a permutation of the flow graph is defined to increase performance (step  730 ). As used herein, a permutation of the flow graph can include any suitable implementation of any suitable portion of the flow graph that provides logical equivalence of tuples. A permutation can include, for example, reordering operators, coalescing operators, and/or splitting operators. The streams manager requests the cloud manager provision VMs for the permutation of the flow graph (step  740 ). The streams manager generates and runs the permutation in the VMs in parallel with the existing flow graph and compares the performance of the permutation with the performance of the corresponding existing portion of the flow graph (step  750 ). When the performance of the permutation is greater than the performance of the original (step  760 =YES), the streams manager modifies the flow graph to use the permutation (step  770 ). When the performance of the permutation is not greater than the original (step  760 =NO), method  700  loops back to step  710  and continues. 
     The determination of whether the permutation performance is greater than performance of the corresponding original portion of the flow graph in step  760  can include any suitable threshold for making the decision. A simple example will illustrate. If the performance of the permutation is only 1% greater than the performance of the original portion of the flow graph, the expense of implementing the permutation may exceed its benefits. For example, due to the cost of implementing a portion of the flow graph in a cloud, one might specify the performance of the permutation implemented in the cloud must exceed the performance of the original portion of the flow graph by 20%. Of course, any suitable threshold, criteria or heuristic could be used in determining whether the performance of the permutation exceeds the performance of the original portion of the flow graph enough to justify making the change. Step  760  herein includes using any suitable threshold, criteria or heuristic for determining whether the performance of the permutation is sufficiently greater than the original to justify making the change. 
     As shown in  FIG. 7 , the streams manager may try different permutations when the streams manager determines performance of a streaming application represented by a flow graph needs to be increased. The streams manager may thus experiment with different permutations on an ongoing basis in an effort to dynamically increase the performance of the streaming application. This allows the streaming application to dynamically evolve over time. 
     Examples are now discussed to illustrate different permutations that could be generated for a flow graph. A sample flow graph  800  is shown, which represents a sample streaming application.  FIG. 9  shows examples of permutation types, and includes permutations that reorder operators, coalesce operators, and split operators. Other permutation types not listed are within the scope of the disclosure and claims herein. 
     Referring to  FIG. 10 , we assume the streams manager determines from some threshold, criteria or heuristic that the performance of operators A, B, C and D in  FIG. 8  needs to be increased. The streams manager determines that a permutation that reorders operators B and C might improve performance. The streams manager requests the cloud manager to provision four VMs, one for each operator. The streams manager then constructs a parallel path shown at A′, C′, B′ and D′, all of which are implemented in VMs, as shown in  FIG. 10 . The newly-deployed permutation is then run in parallel with the existing corresponding portion of the flow graph. The streams manager can then compare the performance of the original portion of the flow graph A, B, C and D to the performance of the permutation A′, C′, B′ and D′. We assume for this example that reordering operators B and C as shown in the permutation results in sufficient increase in performance that the streams manager modifies the flow graph so the original operators A, B, C and D are replaced with the permutation A′, C′, B′ and D′, as shown in  FIG. 11 . 
     Referring to  FIG. 12 , we again assume the streams manager determines from some threshold, criteria or heuristic that the performance of operators A, B, C and D in  FIG. 8  needs to be increased. The streams manager determines that a permutation that splits operators B and C might improve performance. The streams manager requests the cloud manager to provision six VMs. The streams manager then constructs a parallel path shown at A′, B′, B″, C′, C″ and D′, all of which are implemented in VMs, as shown in  FIG. 12 . The newly-deployed permutation is then run in parallel with the existing corresponding portion of the flow graph. The streams manager can then compare the performance of the original portion of the flow graph A, B, C and D to the performance of the permutation that includes operators A′, B′, B″, C′, C″ and D′. We assume for this example that splitting operators B and C as shown in the permutation results in sufficient increase in performance that the streams manager modifies the flow graph so the original operators A, B, C and D are replaced with the permutation, as shown in  FIG. 13 . 
     Referring to  FIG. 14 , we again assume the streams manager determines from some threshold, criteria or heuristic that the performance of operators A, B, C and D in  FIG. 8  needs to be increased. The streams manager determines that a permutation that coalesces operators B and C might improve performance. The streams manager requests the cloud manager to provision three VMs. The streams manager then constructs a parallel path shown at A′, BC′ and D′, all of which are implemented in VMs, as shown in  FIG. 14 . The newly-deployed permutation is then run in parallel with the existing corresponding portion of the flow graph. The streams manager can then compare the performance of the original portion of the flow graph A, B, C and D to the performance of the permutation that includes operators A′, B C′ and D′. We assume for this example that coalescing operators B and C as shown in the permutation results in sufficient increase in performance that the streams manager modifies the flow graph so the original operators A, B, C and D are replaced with the permutation A′, BC′ and D′, as shown in  FIG. 15 . 
     In the examples given above, for the sake of illustration, a VM was provisioned for each operator in each permutation. Of course, multiple operators could be implemented in a single VM. The disclosure and claims herein expressly extend to any suitable number of operators implemented in any suitable number of VMs. 
     In one specific implementation, the original flow graph shown in  FIG. 8  could be implemented on a dedicated computer system, while the permutations are implemented in VMs in a cloud. With this implementation, the resulting flow graphs with permutations shown in  FIGS. 11, 13 and 15  will include a hybrid of operators implemented on a dedicated computer system with operators implemented in a cloud. In an alternative implementation, the original flow graph shown in  FIG. 8  could also be hosted on one or more VMs in a cloud, and the permutations could also be hosted in the same or a different cloud. With this implementation, the resulting flow graphs with permutations shown in  FIGS. 11, 13 and 15  will include operators that are all implemented in a cloud. Note also that multiple clouds could be used. Thus, the original flow graph shown in  FIG. 8  could be implemented in a private cloud, while the permutations could be implemented in a public cloud. 
     The disclosure and claims herein relate to a streams manager that monitors performance of a streaming application, and when the performance needs to be improved, the streams manager automatically requests virtual machines from a cloud manager. In response, the cloud manager provisions one or more virtual machines in a cloud. The streams manager builds a permutation of a flow graph for the streaming application using the virtual machine(s), runs the permutation in parallel with the corresponding portion of the flow graph, and compares the performance of the original portion of the flow graph to the performance of the permutation. When the performance of the permutation exceeds the performance of the original part of the flow graph, the streams manager modifies the flow graph so the permutation replaces the original part of the flow graph. In this manner a streaming application can dynamically evolve to increase its performance as needed. 
     One skilled in the art will appreciate that many variations are possible within the scope of the claims. Thus, while the disclosure is particularly shown and described above, it will be understood by those skilled in the art that these and other changes in form and details may be made therein without departing from the spirit and scope of the claims.