Session memory for static variables and across call memory needsĬall memory for variables that exist within a call Garbage collection for the client that created the session The Oracle JVM manages the following within the session:Īll the objects referenced by static Java variables, all the objects referred to by these objects, and so on, till their transitive closure The entire state of your Java program is private and exists for your entire session. During a call, you can store objects in static fields of different classes, which will be available in the next session. Because each client runs the Java application calls within its own session, activities of each client are separate from any other client. ![]() ![]() No client can access the static variables of other clients, because the memory is not available across session boundaries. Variables defined as static are local to the client. The underlying server environment hides the details associated with session, network, state, and other shared resource management issues from the Java code. The Oracle JVM maximizes sharing read-only data between clients and emphasizes a minimum amount of per-session incremental footprint, to maximize performance for multiple clients. Every call from a single client is managed within its own session, and calls from each client is handled separately. Within a session, the Oracle JVM manages the scalability of applications. It appears to the client as if a separate, individual JVM was started for each session, although the implementation is more efficient than this seems to imply. Within a session, the client has its own Java environment. This is referred to as a call.Ĭontinues to work within the session, performing as many calls as required. Within the context of a session, the client performs the following:Ĭonnects to the database and opens a session. Queue.Figure 2-1 Java Environment Within Each Database Sessionĭescription of "Figure 2-1 Java Environment Within Each Database Session" Under these conditions, we don't recommend setting the number of maximum Because no additional attempts to deliver messages are made In this case,Īmazon SQS records the message as delivered at least once, although the consumer has Successfully from a ReceiveMessage API method call. Receive a message even when Amazon SQS marks the message as delivered while returning Avoiding inconsistent message processingīecause Amazon SQS is a distributed system, it is possible for a consumer to not In the same example above, the message is deleted from the dead-letter queue after 4 days and the ApproximateAgeOfOldestMessage is 4 days. The ApproximateAgeOfOldestMessage metric indicates when the message moved to the dead-letter queue. To always set the retention period of a dead-letter queue to be longer than theįor FIFO queues, the enqueue timestamp resets when the message is moved to a dead-letter queue. If the dead-letter queue's retention period is 4 days, the message is deleted from the dead-letter queue after 3 daysĪnd the ApproximateAgeOfOldestMessage is 3 days. The dead-letter queue, not when the message was originally sent.įor example, assume that a message spends 1 day in the original queue before it's moved to a dead-letter queue. TheĪpproximateAgeOfOldestMessage metric indicates when the message moved to When a message is moved to a dead-letter queue, the enqueue timestamp is unchanged. Metric by giving an incorrect age of the poison pill message.Ĭonfiguring a dead-letter queue helps avoid false alarms whenįor standard queues, the expiration of a message is always based on its original enqueue timestamp. Including a poison pill message in a queue can distort the Pill messages (messages that are received but Reduces the possibility of exposing you to poison Using a dead-letter queue decreases the number of messages and The redrive policy redirects messages to a dead-letter queueĪfter the source queue fails to process a message a specified For more information, see Amazon SQS short and long polling.įor optimal message processing, use the following strategies: (when there are no messages available for a ReceiveMessage request) and falseĮmpty responses (when messages are available but aren't included in a response). Long polling helps reduce the cost of using Amazon SQS by eliminating the number of empty responses The maximum long polling wait time is 20 seconds. ![]() When the wait time for the ReceiveMessage API action is greater than 0, long polling Same results, allow a longer pause (for example, 400 ms). For subsequent use of ReceiveMessage that gives the ![]() If you don't use the AWS SDK features for retry and backoff, allow a pause (for example,Ģ00 ms) before retrying the ReceiveMessageĪction after receiving no messages, a timeout, or an error message fromĪmazon SQS. For more information, see Error Retries and If you use an AWS SDK, you already have automaticĭisposal.
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