Cancel Button Bug: Query Won't Stop After Immediate Click

by Felix Dubois 58 views

Hey guys! We've got a bug report here about a tricky issue with the cancel button in the WebUI. It seems like when you click "Run" and then frantically click "Cancel" right after, the query just keeps on chugging along. Let's dive into the details and figure out what's going on.

Problem Description

So, the main issue we're tackling is that the cancel button isn't doing its job when you click it super quickly after hitting the "Run" button. This is happening in the WebUI, and it's definitely not the behavior we're expecting. Imagine you accidentally hit "Run" on a massive query and then immediately try to stop it – only to find out it's too late! This can lead to wasted resources and a frustrating user experience. We need to ensure that users can reliably stop queries, especially when they realize they've made a mistake or need to adjust their search.

Expected vs. Actual Behavior

Ideally, clicking the "Cancel" button should immediately halt the query execution. That's what users expect, and that's the standard behavior for most applications. However, in this case, the query continues to run even after the "Cancel" button is clicked. This discrepancy between expected behavior and actual behavior is a clear indication of a bug that needs fixing. It's important to address this because it directly impacts the usability and responsiveness of the WebUI. Users need to have confidence that the controls they interact with are working as intended. The cancel button is a critical control for managing queries, and its failure can lead to a negative user experience. Let's not forget that a responsive and intuitive interface is key to user satisfaction, so ironing out these kinks is essential for maintaining a positive perception of the system. We need to dig deep into the code and figure out why this seemingly simple action isn't working as expected. Is it a timing issue? A problem with the event handling? Or something more fundamental in the query processing logic? Whatever the cause, we need to get to the bottom of it to ensure a smooth and predictable user experience.

Suspected Cause and Potential Resolution

The suspected culprit behind this issue is the way Presto handles cancel requests. It appears that Presto's cancel route might be returning a success message even if the queries haven't actually been submitted yet. This means that our WebUI receives a confirmation that the query has been cancelled, but in reality, the query is still running in the background. This is a classic case of asynchronous behavior causing confusion. The client (WebUI) thinks the operation is complete, while the server (Presto) is still processing. A potential resolution lies in correctly handling the query status within the client. A future pull request (PR) might address this by ensuring that the client accurately reflects the query's state. However, we also need to consider the RESTful API design. If users are directly interacting with the API, they might encounter the same issue. Therefore, a thorough review of the API's behavior and response codes is necessary to prevent this problem from recurring in different contexts. We need to make sure that the API provides clear and accurate feedback about the query status, allowing clients to reliably determine whether a query has been successfully cancelled. This might involve updating the API to provide more granular status updates or implementing a mechanism for clients to poll the query status until it reaches a terminal state. Ultimately, the goal is to create a robust and predictable system where users can confidently manage their queries without encountering unexpected behavior.

Additional Context and References

This bug was reported by @hoophalab, so a big shoutout to them for bringing this to our attention! It's also important to note that this issue is not related to PR #1191, which focuses on logging format in the cancel route. So, we can rule that out as a potential cause. This particular bug seems to be specific to the WebUI search functionality, which means we need to focus our debugging efforts in that area. It's crucial to understand the scope of the problem to avoid wasting time investigating unrelated code. Knowing that it's tied to the WebUI search narrows down the potential areas of concern and allows us to be more efficient in our troubleshooting. We can examine the code responsible for handling search queries and the interaction with the cancel button to identify the root cause. Maybe there's a race condition, a missed event, or a misunderstanding in the way the client and server communicate. By focusing on the specific area affected, we can increase our chances of finding a solution quickly and effectively. Remember, clear communication and accurate reporting are key to successful bug fixing. Thanks to @hoophalab's detailed report, we have a solid starting point for our investigation.

References and Further Reading

For those who want to dive deeper into this issue, here are some relevant links:

These links provide valuable context and background information about the bug and its potential solutions. The original discussion thread contains the initial report and subsequent discussions, offering insights into the problem from different perspectives. The related PR, while not directly addressing this bug, touches upon the cancel route and might provide some clues or related information. By reviewing these resources, developers can gain a more comprehensive understanding of the issue and its place within the larger codebase. This can help them to make more informed decisions about how to approach the fix and ensure that the solution is consistent with the overall design and architecture of the system. Remember, thorough research is a crucial step in the bug fixing process, and these references provide a valuable starting point for anyone working on this issue.

Bug Details

Description

Let's break down the bug description in more detail. The core of the problem is that the cancel button in the WebUI fails to stop a query if it's clicked immediately after the "Run" button. This might sound like a minor issue, but it can have significant implications for user experience and system performance. Imagine a scenario where a user accidentally triggers a long-running query or realizes that their search criteria are incorrect. They would naturally expect to be able to stop the query by clicking the "Cancel" button. However, if the button doesn't work as expected, the query will continue to run, consuming resources and potentially delaying other operations. This can lead to frustration and a perception of unreliability. Furthermore, if multiple users encounter this issue, it could strain system resources and impact overall performance. Therefore, it's crucial to address this bug promptly to prevent potential negative consequences. The description highlights a specific timing issue, which suggests that the problem might be related to the asynchronous nature of the query execution process. There could be a race condition or a delay in the communication between the WebUI and the backend system. To diagnose the issue effectively, we need to examine the code that handles the "Cancel" button click and the mechanisms for stopping queries. This might involve debugging the JavaScript code in the WebUI, as well as the backend API endpoints responsible for query management. A thorough understanding of the system's architecture and the interactions between different components is essential for identifying the root cause and implementing a robust solution. Remember, a clear and concise bug description is a valuable asset in the debugging process. It helps developers understand the problem quickly and efficiently, allowing them to focus their efforts on the most relevant areas of the codebase.

Expected Behavior

The expected behavior is straightforward: when a user clicks the "Cancel" button, the query should be immediately stopped. This is a fundamental principle of user interface design – controls should behave predictably and reliably. Users should have confidence that their actions will have the intended effect. In this case, the "Cancel" button is a crucial control for managing queries, and its failure can lead to a negative user experience. Imagine a user who has submitted a complex query that is taking a long time to execute. If they realize that the query is not producing the desired results or if they need to make changes, they should be able to stop the query without delay. This is not only a matter of convenience but also of resource management. Unnecessary queries can consume valuable processing power and memory, potentially impacting the performance of other applications and services. Therefore, a functional "Cancel" button is essential for maintaining system efficiency. The expected behavior also aligns with the principle of providing users with control over their interactions with the system. Users should feel empowered to manage their queries and stop them when necessary. This fosters a sense of trust and confidence in the system. If the "Cancel" button fails to work, it can undermine this trust and lead to frustration. To ensure that the "Cancel" button behaves as expected, we need to carefully examine the underlying mechanisms for stopping queries. This might involve looking at the communication between the WebUI and the backend system, as well as the query execution engine itself. A thorough understanding of these components is essential for implementing a reliable solution.

Actual Behavior

Unfortunately, the actual behavior deviates from the expected behavior. The query continues running even after the "Cancel" button is clicked immediately after "Run". This is a critical issue because it undermines the user's ability to control query execution. Users rely on the "Cancel" button to stop queries when needed, whether it's due to a mistake in the query, a change in requirements, or simply a desire to free up resources. When the button fails to function as expected, it creates a frustrating and potentially disruptive experience. Imagine a scenario where a user accidentally submits a massive query that could take hours to complete. If the "Cancel" button doesn't work, they are stuck with a running query that consumes resources and prevents them from performing other tasks. This can have a significant impact on their productivity and the overall performance of the system. The discrepancy between the expected and actual behavior also indicates a potential flaw in the system's design or implementation. There might be a timing issue, a race condition, or a misunderstanding in the way the WebUI and the backend system communicate. To diagnose the problem effectively, we need to investigate the sequence of events that occur when the "Run" and "Cancel" buttons are clicked. This might involve analyzing network traffic, examining logs, and stepping through the code in a debugger. A thorough understanding of the system's architecture and the interactions between different components is essential for identifying the root cause and implementing a robust solution. Remember, the goal is to ensure that the "Cancel" button works reliably in all situations, providing users with the control they expect and need.

Suspected Cause

The suspected cause of this bug is related to how Presto, the underlying query engine, handles cancel requests. It seems that Presto's cancel route might be returning a success message even if the query hasn't been fully submitted yet. This creates a disconnect between what the WebUI perceives and what's actually happening in the backend. The WebUI receives a confirmation that the query has been cancelled, leading it to believe that the operation has been stopped. However, in reality, the query might still be running in Presto's internal processing queue. This can occur if the "Cancel" button is clicked very soon after the "Run" button, before the query has had a chance to fully register with Presto. The timing of these events is crucial, and the asynchronous nature of the query submission and cancellation processes can lead to this type of race condition. To understand this further, we need to examine the communication flow between the WebUI and Presto's API. When the "Run" button is clicked, the WebUI sends a request to Presto to execute the query. Simultaneously, when the "Cancel" button is clicked, the WebUI sends a separate request to cancel the query. However, if the cancel request arrives at Presto before the query has been fully submitted, Presto might return a success message without actually cancelling the query. This is because Presto might not yet have a record of the query in its active query list. To verify this hypothesis, we need to analyze the logs from both the WebUI and Presto. We can look for the timestamps of the "Run" and "Cancel" requests and correlate them with the query execution status in Presto. This will help us determine if there is a timing discrepancy that could explain the observed behavior. Additionally, we should review the code that handles the cancel request in Presto to ensure that it correctly identifies and terminates running queries. A potential solution might involve adding a mechanism to check if the query has been fully submitted before attempting to cancel it. This could involve tracking the query submission status and delaying the cancel request until the query is active in Presto's processing queue. Remember, a thorough understanding of the underlying systems and their interactions is crucial for diagnosing and resolving this type of complex issue.

Potential Resolution

The potential resolution for this bug lies in correctly handling the query status within the client (WebUI). As mentioned earlier, the issue seems to stem from the WebUI receiving a success message from Presto's cancel route even if the query hasn't actually been submitted yet. Therefore, the client needs to be more intelligent about tracking the query's state and not rely solely on the initial response from the cancel route. A future pull request (PR) is expected to address this by implementing a more robust query status tracking mechanism in the client. This might involve introducing a state machine or a similar construct to manage the query's lifecycle. The client would then track the query's progress through different stages, such as "Submitting," "Running," "Cancelling," and "Cancelled." By maintaining a clear understanding of the query's state, the client can avoid misinterpreting responses from the backend and provide a more accurate representation of the query's status to the user. However, while fixing the client-side logic is crucial, we also need to consider the RESTful API design. If users are interacting with the API directly, they might encounter the same issue. Therefore, we should review the API's behavior and response codes to ensure that they provide clear and accurate feedback about the query status. This might involve updating the API to provide more granular status updates or implementing a mechanism for clients to poll the query status until it reaches a terminal state. Another potential solution could be to modify Presto's cancel route to delay the success response until the query has been fully cancelled. This would ensure that the client only receives a success message when the query has actually been terminated. However, this approach might introduce performance overhead and could impact the responsiveness of the system. Therefore, it's important to carefully evaluate the trade-offs before implementing this type of change. Ultimately, the goal is to create a robust and predictable system where users can confidently manage their queries without encountering unexpected behavior. This requires a holistic approach that addresses both the client-side and server-side aspects of the issue.

Additional Context

Adding some additional context helps to paint a clearer picture of the situation. As mentioned, this issue was reported by @hoophalab, highlighting the importance of user feedback in identifying and addressing bugs. It's crucial to have a system in place for users to report issues and for developers to respond promptly. This fosters a collaborative environment and helps to improve the overall quality of the software. It's also important to note that this bug is not related to PR #1191, which focuses on logging format in the cancel route. This helps to narrow down the scope of the investigation and avoid wasting time on unrelated code. Knowing that the issue is not connected to logging format allows developers to focus their attention on the core query cancellation logic. This can save time and effort in the debugging process. Furthermore, the fact that this bug affects the WebUI search functionality provides another clue about the potential cause. This suggests that the issue might be specific to the way search queries are handled in the WebUI and could be related to the interactions between the WebUI and the backend search service. By focusing on the WebUI search functionality, developers can narrow down the potential areas of concern and increase their chances of finding a solution quickly. In addition to these specific details, it's also helpful to consider the broader context of the system's architecture and the different components involved in query execution and cancellation. This can provide valuable insights into the potential interactions and dependencies that might be contributing to the issue. Remember, a comprehensive understanding of the system is essential for effective bug fixing.

References

Original Discussion

Referencing the original discussion (https://github.com/y-scope/clp/pull/1191#discussion_r123456789) is crucial for understanding the initial report and the subsequent discussions surrounding this bug. The discussion thread often contains valuable insights from different perspectives, including the reporter, developers, and other stakeholders. It might include details about the specific steps to reproduce the bug, the expected behavior, the actual behavior, and potential causes. By reviewing the original discussion, developers can gain a deeper understanding of the issue and its impact. The discussion might also reveal related issues or dependencies that need to be considered. For example, it might highlight similar bugs that have been reported in the past or identify areas of the code that are particularly prone to errors. In addition to technical details, the original discussion can also provide valuable context about the user's experience and the business impact of the bug. This can help developers prioritize the fix and ensure that the solution addresses the user's needs. Furthermore, the discussion thread can serve as a valuable resource for future reference. It provides a record of the bug's history, including the steps taken to diagnose and resolve it. This can be helpful for developers who encounter similar issues in the future. When reviewing the original discussion, it's important to pay attention to the different perspectives and opinions expressed. This can help to identify potential disagreements or misunderstandings that need to be addressed. It's also important to consider the tone and language used in the discussion, as this can provide clues about the urgency and severity of the bug. Remember, the original discussion is a valuable resource for understanding the bug and its context. It's essential to review it carefully before attempting to fix the issue.

Related PR

The related PR (https://github.com/y-scope/clp/pull/1191) , while not directly addressing the bug, might contain relevant information or changes that could impact the fix. It's important to review the PR to understand its scope and the modifications it introduces. The PR might include changes to the cancel route, the query execution logic, or other related components. By understanding these changes, developers can ensure that the bug fix is compatible with the existing codebase and doesn't introduce any new issues. The PR might also contain discussions about the cancel route and its behavior, which could provide valuable insights into the cause of the bug. For example, the discussion might reveal potential race conditions or timing issues that could be contributing to the problem. In addition to the code changes and discussions, the PR might also include tests that cover the cancel route. These tests can be helpful for verifying the bug fix and ensuring that it doesn't break existing functionality. By running the tests, developers can gain confidence that the solution is robust and reliable. When reviewing the PR, it's important to pay attention to the comments and feedback from other developers. This can help to identify potential issues or concerns that need to be addressed. It's also important to consider the overall design and architecture of the system and ensure that the bug fix aligns with these principles. Remember, the related PR can provide valuable context and information about the bug and its potential solutions. It's essential to review it carefully before attempting to implement the fix.

Conclusion

Alright, guys, that's the breakdown of this tricky bug with the cancel button. It's definitely something we need to tackle to ensure a smooth user experience. By understanding the suspected cause and potential resolutions, we're well on our way to squashing this bug and making our WebUI even better. Thanks for tuning in, and let's get this fixed!