Patent Publication Number: US-9848047-B2

Title: High density hosting for messaging service

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 13/419,435, filed on Mar. 14, 2012, now U.S. Pat. No. 9,344,391, issued on May 17, 2016, the disclosure of which is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     The past several decades has seen a phenomenal growth in capabilities of computers. A typical computer of today often has many times the processing capabilities and storage capabilities as a typical computer of a decade ago. Even with the phenomenal increase in processing and storage capabilities, an inefficient algorithm compounded by many parallel requests may cause performance issues. While obtaining a faster computer or more computers may address the performance issues, such solutions may be expensive to purchase, power, and maintain. 
     The subject matter claimed herein is not limited to embodiments that solve any disadvantages or that operate only in environments such as those described above. Rather, this background is only provided to illustrate one exemplary technology area where some embodiments described herein may be practiced. 
     SUMMARY 
     Briefly, aspects of the subject matter described herein relate migrating message for a messaging service. In aspects, a determination is made that messages need to be migrated based on a threshold being crossed. In response, an agent is instructed to migrate data associated with the messages to another location. The agent uses various factors to determine one or more queues to migrate. While a queue is being migrated, during a first portion of the migration, messages may be added to and removed from the queue as senders send new messages and receivers consume messages. During a second portion of the migration, the queue is frozen to disallow the queue to be used for receiving new messages and delivering queued messages. The migration may be orchestrated to attempt to achieve certain goals. 
     This Summary is provided to briefly identify some aspects of the subject matter that is further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     The phrase “subject matter described herein” refers to subject matter described in the Detailed Description unless the context clearly indicates otherwise. The term “aspects” should be read as “at least one aspect.” Identifying aspects of the subject matter described in the Detailed Description is not intended to identify key or essential features of the claimed subject matter. 
     The aspects described above and other aspects of the subject matter described herein are illustrated by way of example and not limited in the accompanying figures in which like reference numerals indicate similar elements and in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram representing an exemplary general-purpose computing environment into which aspects of the subject matter described herein may be incorporated; 
         FIG. 2  is a block diagram that represents an exemplary environment in which aspects of the subject matter described herein may operate; 
         FIG. 3  is a block diagram representing an exemplary messaging service and associated data stores in accordance with aspects of the subject matter described herein; 
         FIG. 4  is a block diagram that generally represents exemplary actions that may occur at a messaging service in accordance with aspects of the subject matter described herein; and 
         FIG. 5  is a block diagram that generally represents exemplary actions that may occur from a sender perspective in accordance with aspects of the subject matter described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Definitions 
     As used herein, the term “includes” and its variants are to be read as open-ended terms that mean “includes, but is not limited to.” The term “or” is to be read as “and/or” unless the context clearly dictates otherwise. The term “based on” is to be read as “based at least in part on.” The terms “one embodiment” and “an embodiment” are to be read as “at least one embodiment.” The term “another embodiment” is to be read as “at least one other embodiment.” 
     As used herein, terms such as “a,” “an,” and “the” are inclusive of one or more of the indicated item or action. In particular, in the claims a reference to an item generally means at least one such item is present and a reference to an action means at least one instance of the action is performed. 
     Sometimes herein the terms “first”, “second”, “third” and so forth may be used. Without additional context, the use of these terms in the claims is not intended to imply an ordering but is rather used for identification purposes. For example, the phrases “first version” and “second version” do not necessarily mean that the first version is the very first version or was created before the second version or even that the first version is requested or operated on before the second version. Rather, these phrases are used to identify different versions. 
     Headings are for convenience only; information on a given topic may be found outside the section whose heading indicates that topic. 
     Other definitions, explicit and implicit, may be included below. 
     Exemplary Operating Environment 
       FIG. 1  illustrates an example of a suitable computing system environment  100  on which aspects of the subject matter described herein may be implemented. The computing system environment  100  is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of aspects of the subject matter described herein. Neither should the computing environment  100  be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment  100 . 
     Aspects of the subject matter described herein are operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well-known computing systems, environments, or configurations that may be suitable for use with aspects of the subject matter described herein comprise personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microcontroller-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, personal digital assistants (PDAs), gaming devices, printers, appliances including set-top, media center, or other appliances, automobile-embedded or attached computing devices, other mobile devices, distributed computing environments that include any of the above systems or devices, and the like. 
     Aspects of the subject matter described herein may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, and so forth, which perform particular tasks or implement particular abstract data types. Aspects of the subject matter described herein may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices. 
     With reference to  FIG. 1 , an exemplary system for implementing aspects of the subject matter described herein includes a general-purpose computing device in the form of a computer  110 . A computer may include any electronic device that is capable of executing an instruction. Components of the computer  110  may include a processing unit  120 , a system memory  130 , and a system bus  121  that couples various system components including the system memory to the processing unit  120 . The system bus  121  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a 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, Peripheral Component Interconnect (PCI) bus also known as Mezzanine bus, Peripheral Component Interconnect Extended (PCI-X) bus, Advanced Graphics Port (AGP), and PCI express (PCIe). 
     The processing unit  120  may be connected to a hardware security device  122 . The security device  122  may store and be able to generate cryptographic keys that may be used to secure various aspects of the computer  110 . In one embodiment, the security device  122  may comprise a Trusted Platform Module (TPM) chip, TPM Security Device, or the like. 
     The computer  110  typically includes a variety of computer-readable media. Computer-readable media can be any available media that can be accessed by the computer  110  and includes both volatile and nonvolatile media, and removable and non-removable media. By way of example, and not limitation, computer-readable media may comprise computer storage media and communication media. 
     Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer-readable instructions, data structures, program modules, or other data. Computer storage media includes RAM, ROM, EEPROM, solid state storage, flash memory or other memory technology, CD-ROM, digital versatile discs (DVDs) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the computer  110 . 
     Communication media typically embodies computer-readable instructions, data structures, program modules, or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer-readable media. 
     The system memory  130  includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM)  131  and random access memory (RAM)  132 . A basic input/output system  133  (BIOS), containing the basic routines that help to transfer information between elements within computer  110 , such as during start-up, is typically stored in ROM  131 . RAM  132  typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit  120 . By way of example, and not limitation,  FIG. 1  illustrates operating system  134 , application programs  135 , other program modules  136 , and program data  137 . 
     The computer  110  may also include other removable/non-removable, volatile/nonvolatile computer storage media. By way of example only,  FIG. 1  illustrates a hard disk drive  141  that reads from or writes to non-removable, nonvolatile magnetic media, a magnetic disk drive  151  that reads from or writes to a removable, nonvolatile magnetic disk  152 , and an optical disc drive  155  that reads from or writes to a removable, nonvolatile optical disc  156  such as a CD ROM or other optical media. Other removable/non-removable, volatile/nonvolatile computer storage media that can be used in the exemplary operating environment include magnetic tape cassettes, flash memory cards and other solid state storage devices, digital versatile discs, other optical discs, digital video tape, solid state RAM, solid state ROM, and the like. The hard disk drive  141  may be connected to the system bus  121  through the interface  140 , and magnetic disk drive  151  and optical disc drive  155  may be connected to the system bus  121  by an interface for removable nonvolatile memory such as the interface  150 . 
     The drives and their associated computer storage media, discussed above and illustrated in  FIG. 1 , provide storage of computer-readable instructions, data structures, program modules, and other data for the computer  110 . In  FIG. 1 , for example, hard disk drive  141  is illustrated as storing operating system  144 , application programs  145 , other program modules  146 , and program data  147 . Note that these components can either be the same as or different from operating system  134 , application programs  135 , other program modules  136 , and program data  137 . Operating system  144 , application programs  145 , other program modules  146 , and program data  147  are given different numbers herein to illustrate that, at a minimum, they are different copies. 
     A user may enter commands and information into the computer  110  through input devices such as a keyboard  162  and pointing device  161 , commonly referred to as a mouse, trackball, or touch pad. Other input devices (not shown) may include a microphone for inputting voice or other audio, joystick, game pad, satellite dish, scanner, a touch-sensitive screen, a writing tablet, a camera for inputting gestures or other visual input, or the like. These and other input devices are often connected to the processing unit  120  through a user input interface  160  that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). 
     A monitor  191  or other type of display device is also connected to the system bus  121  via an interface, such as a video interface  190 . In addition to the monitor, computers may also include other peripheral output devices such as speakers  197  and printer  196 , which may be connected through an output peripheral interface  195 . 
     The computer  110  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  180 . The remote computer  180  may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  110 , although only a memory storage device  181  has been illustrated in  FIG. 1 . The logical connections depicted in  FIG. 1  include a local area network (LAN)  171  and a wide area network (WAN)  173 , but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets, and the Internet. 
     When used in a LAN networking environment, the computer  110  is connected to the LAN  171  through a network interface or adapter  170 . When used in a WAN networking environment, the computer  110  may include a modem  172  or other means for establishing communications over the WAN  173 , such as the Internet. The modem  172 , which may be internal or external, may be connected to the system bus  121  via the user input interface  160  or other appropriate mechanism. In a networked environment, program modules depicted relative to the computer  110 , or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation,  FIG. 1  illustrates remote application programs  185  as residing on memory device  181 . It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. 
     Migration 
     As mentioned previously, addressing issues of performance by purchasing, powering, and maintaining computer resources may be costly.  FIGS. 2-3  are block diagrams representing an exemplary arrangement of components in which aspects of the subject matter described herein may operate. The components illustrated in  FIGS. 2-3  are exemplary and are not meant to be all-inclusive of components that may be needed or included. In other embodiments, the components and/or functions described in conjunction with  FIG. 2-3  may be included in other components (shown or not shown) or placed in subcomponents without departing from the spirit or scope of aspects of the subject matter described herein. In some embodiments, the components and/or functions described in conjunction with  FIG. 2-3  may be distributed across multiple devices. 
       FIG. 2  is a block diagram that represents an exemplary environment in which aspects of the subject matter described herein may operate. Turning to  FIG. 2 , the system  205  may include various components that may be one or more computing devices. Such devices may include, for example, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microcontroller-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, cell phones, personal digital assistants (PDAs), gaming devices, printers, appliances including set-top, media center, or other appliances, automobile-embedded or attached computing devices, other mobile devices, distributed computing environments that include any of the above systems or devices, and the like. 
     Where the system  205  comprises a single device, an exemplary device that may be configured to act as the system  205  comprises the computer  110  of  FIG. 1 . Where the system  205  comprises multiple devices, each of the multiple devices may comprise one or more similarly or differently configured computers such as the computer  110  of  FIG. 1 . 
     The components of the system  205  may include a sender  210 , a messaging service  211 , a receiver  212 , a store  213 , and other components (not shown). As used herein, the term component is to be read to include all or a portion of one or more devices, a collection of one or more software modules or portions thereof, some combination of one or more software modules or portions thereof and one or more devices or portions thereof, and the like. 
     The various components of the system  205  may be located close to each other or even on the same machine or may be distributed across the world. The various components may communicate with each other via one or more local area networks, wide area networks, direct connections, virtual connections, private networks, virtual private networks, the Internet, some combination of the above, and the like. 
     The store  213  is any storage media capable of providing access to data. Access as used herein may include reading data, writing data, deleting data, updating data, a combination including two or more of the above, and the like. The store  213  may comprise hard disk storage, other non-volatile storage, volatile memory such as RAM, other storage, some combination of the above, and the like and may be distributed across multiple devices. The store  213  may be external, internal, or include components that are both internal and external to the system  205 . 
     The term data is to be read broadly to include anything that may be represented by one or more computer storage elements. Logically, data may be represented as a series of 1&#39;s and 0&#39;s in volatile or non-volatile memory. In computers that have a non-binary storage medium, data may be represented according to the capabilities of the storage medium. Data may be organized into different types of data structures including simple data types such as numbers, letters, and the like, hierarchical, linked, or other related data types, data structures that include multiple other data structures or simple data types, and the like. Some examples of data include information, program code, program state, program data, other data, and the like. 
     The sender  210  may send messages to the receiver  212  by sending the messages to the messaging service  211 . Although only one sender is shown in  FIG. 2 , it is to be understood that there may be a plurality of different senders that send messages to the messaging service  211  for delivery to the receiver  212 . 
     Likewise, although only one receiver  212  is shown in  FIG. 2 , in other embodiments, there may be a plurality of receivers receiving messages from the messaging service  211 . 
     The messaging service  211  may store messages in the store  213  until the messages are delivered to the receiver  212 . In one implementation, the messaging service  211  may notify the receiver  212  that there are messages for the receiver  212 . In another implementation, the messaging service  211  may not proactively inform the receiver  212  of queued messages but may instead wait for the receiver  212  to ask the messaging service  211  whether there are any messages queued for the receiver  212 . 
     In one implementation, the receiver  212  may receive notification that there are messages for the receiver  212 . In another implementation, the receiver  212  may periodically check with the messaging service  211  to determine whether there are any messages for the receiver  212 . 
     If there are messages queued for the receiver  212 , the receiver  212  may obtain the messages from the messaging service  211  and act on the messages as appropriate. 
       FIG. 3  is a block diagram representing an exemplary messaging service and associated data stores in accordance with aspects of the subject matter described herein. The messaging service may include a gateway  305 , a coordinator  307 , a throttler  309 , message containers  310 - 312 , and other components (not shown). Each message container may be associated with a store (e.g., the stores  315 - 317 ) that may include one or more queue objects. 
     A queue object may include a queue of messages to deliver to a single receiver, a queue of messages where there may be two or more receivers competing for and consuming the messages, a topic, another durable object stored on a store, a combination of two or more of the above, and the like. Where two or more receivers compete for messages of a queue, once one of the receivers has consumed a message from the queue, the message is no longer available for the other receivers to consume. 
     A topic may include a queue of messages that may, though the use of filters, be used to logically create multiple sub queues. A sub queue may be associated with one or more filters. Each filter may use various criteria to determine whether a message in the topic is to be logically placed within a sub queue associated with the filter. In one implementation, the sub queues may be implemented by storing pointers or other identifiers that reference the messages of the topic. 
     A sub queue may be subscribed to by one or more receivers. If a sub queue is subscribed to by a single receiver, that single receiver is allowed to consume the messages of the sub queue. If the sub queue is subscribed to by multiple receivers, the multiple receivers compete for and consume the messages of the sub queue. 
     As used herein, a queue object will sometimes be referred to simply as a queue. Unless the context indicates otherwise, it is to be understood that as used herein, a queue is a shortened name for a queue object. 
     When the space consumed in a store associated with a message container crosses a configurable threshold this may trigger migrating one or more of the queues in the message container to another message container with its associated store. For example, if the message container  310  exceeds 70% of the storage capacity of the store  315 , one or more of the queues of the message container  310  may be migrated to the message container  313  and its associated store  318 . 
     The coordinator  307  may monitor the use of storage on the stores of the messaging service. If the storage usage passes a threshold, and if an additional message container is needed, the coordinator  307  may instantiate a new message container (e.g., the message container  313 ) and associate the new message container with one or more stores (e.g., the store  318 ). A store may be associated with one or more message containers. The coordinator  307  may then cause queues to be migrated from messaging containers that have crossed a threshold. 
     Data that indicates that the coordinator  307  decided to migrate a queue may be persisted in a nonvolatile store for crash recovery, for example. Furthermore, data that indicates that a queue has been moved may be persisted for a configurable period of time to allow, for example, the restoring of messages from a backup that occurred prior to moving the queue. 
     Throughput may be another trigger for moving queues from one messaging container to another. For example, if a messaging container has one or more hot queues that receive messages at a high rate, the messaging container may be overwhelmed and perform sluggishly. The coordinator  307  may monitor throughput of the messaging containers and may instruct messaging containers that have throughput below a threshold to migrate data to other messaging containers. 
     The triggers described above are exemplary. There may be other criteria that the coordinator  307  may monitor to determine whether queues need be migrated without departing from the spirit or scope of aspects of the subject matter described herein. 
     The term messaging container refers to a component that receives messages from one or more senders and provides these messages to one or more receivers. There may be intermediate components between a messaging container and its sender(s) and receiver(s). Based on the order in which messages are received, a messaging container may place the messages received into a queue and may use storage internal and/or external to the messaging container to store the queue. The storage may be volatile and/or nonvolatile and may be implemented by any type or combination of storage mediums mentioned herein. 
     To cause queues to be migrated, the coordinator  307  may instruct a messaging container that has crossed a threshold to move a portion of its queues to one or more other messaging containers identified by the coordinator  307 . The one or more other messaging containers may include one or more of: a newly instantiated messaging container (e.g, the messaging container  313 ), an existing messaging container (e.g., one that has capacity for more queues), a plurality of newly instantiated messaging containers, a plurality of existing messaging containers, a combination of two or more of the above, or the like. Furthermore, multiple queues from one or more messaging containers may be migrated in parallel. 
     In response, the messaging container may determine which of its queues to move. Each messaging container may include a migration agent that handles migrating data to one or more other messaging containers. For example, the messaging containers  310 - 313  may include the migrating agents  320 - 323 , respectively. In selecting queues to migrate, a migration agent may attempt to meet several goals including one or more of minimizing downtime of a queue, minimizing time to accomplish the migration, freeing up enough space to satisfy the coordinator  307 , and the like. The migration agent may determine which queues to move based one or more of the following exemplary factors: 
     1. When the queue was last used; 
     2. Queue size. This may be measured by space used to store the queue, number of messages in the queue, or the like; 
     3. How frequently a queue is used. This is sometimes referred to as “hotness.” In one example, hotness may be measured by average throughput over time where more recent usages are weighted more; and 
     4. Queue type. For example, whether the queue is a queue of messages, a topic, or another type of object may be used as a factor. 
     In one implementation, a migration agent will first determine the times that the queues were last used. If only one queue has the longest time since being last used, that queue may be selected for migration. If multiple queues have the same longest time since being last used, the migration agent may then look at queue size in terms of space used on the store. If one of the queues is larger than all the other queues, this queue may be chosen for migration. If two or more queues both share the largest size, the queue that is least hot may be selected for migration. 
     In one example, a migration agent may sort queues of a messaging container by the three criteria mentioned above and begin migrating queues based on the sorted order until enough space has been freed to satisfy the coordinator  307 . 
     In another implementation, a migration agent may use a formula that weights each of the factors above. For example, an exemplary formula may include: f(x)=w 1 *last used+w 2 *queue size+w 3 *hotness, where * represents multiplication and w 1 , w 2 , and w 3  represent weights. The migration agent may sort the queues based on this formula and may begin migrating queues based on the sorted order until enough space has been freed to satisfy the coordinator  307 . 
     In one implementation, the migrating agent may migrate data for one or more of its queues by performing a set of actions. The set of actions may include, for example: 
     1. Determining a queue to migrate based on one or more factors (e.g., the factors mentioned above). 
     2. Migrating data of the queue while allowing the queue to be used for receiving new messages and delivering queued messages. 
     3. Repeating step 2 until the remaining data in the queue is below a threshold. The threshold may be selected to cause the queue to be frozen for less than a configurable period of time. 
     4. Freezing the queue to disallow the queue to be used for receiving new messages and delivering queued messages. 
     5. Migrating remaining data, if any, of the queue while the queue is frozen. 
     6. Updating data structures of the gateway to indicate that the migrated to messaging container is to be used for the queue. 
     7. Thawing the queue. Thawing allows the queue to be used for receiving new messages and delivering queued messages. 
     8. Updating data structures that indicate that the queue has been migrated. 
     9. Repeating the steps above, if needed, to free additional space. 
     If an error occurs, the queue may be thawed without instruction of the migrating agent. Upon restart, the migrating agent may: 
     1. Detect that it had not completed migrating data of the queue. If the migrating agent detects this, the migrating agent may restart at step 2 above. 
     2. Detect that it had completed migrating data but that step 6 above had not been performed. If the migrating agent detects this, it is possible that more messages have been added to the old queue. Thus, the migrating agent may restart at step 2 above. 
     3. Detect that it had completed migrating data and that steps 2-7 had been completed but that step 8 had not been completed. If the migrating agent detects this, it may resume at step 8. 
     In migrating data, the migrating agent may detect that it is not copying data as fast as data is being inserted into the queue. In this case, the migrating agent may abort migrating the data of the queue, instruct the throttler  309  to reduce the rate at which messages are allowed to be delivered to the queue, or take other actions. 
     In one implementation, there may be a separate throttler for each messaging container. In another implementation, there may be a single throttler for the entire messaging service. The throttler  309  may control the rate at which messages are allowed to be added to a queue. By reducing the rate for a queue, the throttler  309  may assist a migrating agent that is attempting to migrate data of the queue to another messaging container. 
       FIGS. 4-5  are flow diagrams that generally represent exemplary actions that may occur in accordance with aspects of the subject matter described herein. For simplicity of explanation, the methodology described in conjunction with  FIGS. 4-5  is depicted and described as a series of acts. It is to be understood and appreciated that aspects of the subject matter described herein are not limited by the acts illustrated and/or by the order of acts. In one embodiment, the acts occur in an order as described below. In other embodiments, however, the acts may occur in parallel, in another order, and/or with other acts not presented and described herein. Furthermore, not all illustrated acts may be required to implement the methodology in accordance with aspects of the subject matter described herein. In addition, those skilled in the art will understand and appreciate that the methodology could alternatively be represented as a series of interrelated states via a state diagram or as events. 
     Although some indications and are made as to which components are performing what actions, these indications are exemplary only. In other embodiments, actions described as being performed by one component may be performed by another component. For example, in some implementations, a coordinator may perform some of the actions that have been described as being performed by a migrating agent or messaging container and vice versa. 
       FIG. 4  is a block diagram that generally represents exemplary actions that may occur at a messaging service in accordance with aspects of the subject matter described herein. Turning to  FIG. 4 , at block  405 , the actions begin. At block  410 , a determination is made that migration is needed. For example, referring to  FIG. 3 , the coordinator  307  may determine that storage consumed for the messaging container  310  has exceeded a threshold. As another example, the coordinator  307  may determine that the transaction rate of the messaging container  310  has dropped below a threshold. 
     At block  415 , a migrating agent may be instructed to move data to one or more other messaging containers. For example, referring to  FIG. 1 , the coordinator  307  may instantiate a new messaging container  313  and associate the messaging container  313  with the store  318 . The coordinator  307  may then instruct the migrating agent  320  to migrate a specified amount (e.g., 100 GB) of data to the messaging container  310 . In instructing the migrating agent  320  to migrate data to one or more other messaging containers, the coordinator  307  may instruct the migrating agent  320  as to an amount of data that is to be migrated to each messaging container. 
     At block  420 , the messaging container receives the instruction to migrate data to at least one messaging container. For example, referring to  FIG. 3 , the messaging container  310  (e.g., via the migrating agent  320 ) may receive an instruction to migrate a specified amount (e.g., 100 GB) of data to the messaging container  313 . 
     At block  425 , a queue to migrate to another messaging container is determined. This determination may be based on one or more factors including when the queue was last used, size of the queue, and hotness of the queue as mentioned previously. For example, referring to  FIG. 2 , the migrating agent may select Q 4  to migrate if Q 4  was the queue that has not been used the longest. 
     In one exemplary implementation, the migrating agent may determine a queue to migrate by: 
     1. Placing identifiers of the queues into a sorted list by sorting the queues based on first when each queue was last used, second size of each queue, and third hotness of each queue; and 
     2. Selecting the queue associated with the first element of the list. 
     In another exemplary implementation, the migrating agent may determine a queue to migrate by: 
     1. Placing identifiers of the queues into a sorted list by sorting the queues based on a formula:
 
 f ( x )= w   1 *last used+ w   2 *queue size+ w   3 *hotness,
 
where * represents multiplication and w 1 , w 2 , and w 3  represent weights; and
 
     2. Selecting the queue associated with the first element of the list. 
     Based on the teachings herein, those skilled in the art will recognize other mechanisms for determining a queue based on various factors. 
     At block  430 , at least a portion of the queue is migrated while allowing the queue to be used by the messaging container for receiving new messages and delivering queued messages. For example, referring to  FIG. 2 , the migrating agent  320  may begin copying data from the queue to the new messaging container  313 . The migrating agent  320  may copy data from the queue until the remaining data of the queue is below a threshold or until other conditions occur. 
     For example, the migrating agent may determine whether the queue is growing faster than the queue is being migrated. If the queue is growing faster than the queue is being migrated, the migrating agent may abort migrating the queue. 
     As another example, if the migrating agent determines that the queue is growing faster than the queue is being migrated, the migrating agent may throttle the queue by decreasing a rate at which messages are allowed to be added to the queue. 
     Migrating the portion of the queue while allowing queue usage may involve copying a portion of the queue to the destination messaging container, detecting whether the remaining portion of the queue is less than a threshold, and repeating the actions above if and until the remaining portion of the queue is less than the threshold. Because the queue is allowed to receive messages, the remaining portion of the queue may be added to during the migrating activities of the migrating agent. If the remaining portion of the queue is less than the threshold, the actions of block  435  may be performed. 
     In migrating messages from a source messaging container to a destination messaging container, a migrating agent may also delete from the destination messaging container any messages that have been consumed from the queue during the migrating. 
     If a migrating agent repeatedly copies messages from a queue to a destination messaging container to prepare for freezing the queue, the migrating agent need only copy messages that have not already been previously copied from the queue to the destination messaging container. 
     At block  435 , the queue may be frozen. For example, referring to  FIG. 3 , the migrating agent may freeze the queue Q 4 . Freezing the queue to disallow the queue to be used for receiving new messages and delivering queued messages. 
     At block  440 , the remaining data in the queue, if any, may be migrated while the queue is frozen. For example, referring to  FIG. 3 , while the queue Q 4  is frozen, the migrating agent  320  may migrate the remaining data, if any, of the queue Q 4 . 
     At block  445 , the queue is thawed. For example, referring to  FIG. 3 , the migrating agent  320  may thaw the queue Q 4  as all of the data has been migrated to the message container  313 . Thawing allows the queue to be used for receiving new messages and delivering queued messages. Prior to thawing the queue, a data structure (e.g., one used by the gateway  305 ) may be updated to indicate that messages for Q 4  are to be sent to the messaging container to which Q 4  was migrated (e.g., the messaging container  313 ). 
     At block  450 , other actions, if any, may be performed. 
       FIG. 5  is a block diagram that generally represents exemplary actions that may occur from a sender perspective in accordance with aspects of the subject matter described herein. At block  505 , the actions begin. 
     At block  510 , a message is sent to a messaging service. For example, referring to  FIG. 2 , the sender  210  sends a message to the messaging service  211  to be delivered to the receiver  212 . 
     At block  515 , messages may still be sent to the queue even while the queue is being migrated. For example, referring to  FIG. 2 , the sender  210  and other senders (not shown) may continue sending messages to a queue being migrated. 
     At block  520 , while a queue is frozen, messages may not be added to the queue. For example, referring to  FIG. 3 , while the queue Q 4  is frozen, no messages for the queue may be allowed to be added the queue. In one embodiment, a limited number of messages may be held outside the queue for a short time while the queue is frozen. After the queue is thawed, the held messages may be added to the queue. 
     At block  525 , after the queue is thawed, the queue may be ready to receive messages again. For example, referring to  FIG. 3 , after the queue Q 4  is migrated to the messaging container  313 , the queue Q 4  may receive and deliver messages as normal. 
     At block  530 , other actions, if any, may be performed. 
     As can be seen from the foregoing detailed description, aspects have been described related to migrating messages. While aspects of the subject matter described herein are susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit aspects of the claimed subject matter to the specific forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of various aspects of the subject matter described herein.