Hi @Marvin What is the source of this query?

SELECT work_pool.id AS work_pool_id, work_pool.name AS work_pool_name, work_pool.description AS work_pool_description, work_pool.type AS work_pool_type, work_pool.base_job_template AS work_pool_base_job_template, work_pool.is_paused AS work_pool_is_paused, work_pool.default_queue_id AS work_pool_default_queue_id, work_pool.concurrency_limit AS work_pool_concurrency_limit, work_pool.created AS work_pool_created, work_pool.updated AS work_pool_updated 
FROM work_pool 
WHERE work_pool.id IN ($1::UU

It seems that the query you provided does not have a corresponding issue or discussion in the GitHub repository for Prefect. This could mean that the query is either from an internal source code, a private repository, documentation, or from another context not publically discussed in Prefect's GitHub issues. If you are looking for the source of that SQL query within the context of Prefect, it might be part of the Prefect database models or internals dealing with work pools, which are typically used for managing execution resources. However, without further context, it's difficult to precisely pinpoint the origin. If you can provide more information about where you encountered this query or additional context, I might be able to assist you better.

@Marvin Is it possible that these are queries done by agents, querying for job to do?

Yes, it is possible that the SQL query you've shared could be part of the internal logic used by Prefect agents. Agents in Prefect are responsible for querying the orchestration layer to find jobs (flows and tasks) to execute. They need to check for available work that matches certain criteria, such as work that is scheduled for execution and within their assigned work pools or queues. The

work_pool

table mentioned in your query would likely be used to manage different pools of work that can be assigned to agents. Each agent could be configured to pull work from a specific pool, which could be represented by rows in this table. The SQL query looks like it's designed to select information about one or more work pools identified by their IDs (

work_pool.id IN ($1::UU

). This might be a part of the process where an agent checks which work pools it is associated with and retrieves their details to determine if there are any jobs available for execution. Since I can't find a specific GitHub issue related to this query using Prefect 2.x's GitHub search, this suggests that the query might be part of the proprietary codebase or specifics of implementation not discussed in open-source issues. It could also be part of automated database operations within the Prefect core services or a custom extension implemented in a private deployment.

@Marvin what happens after a work was found by the agent, how does it know what specific flow to run?

After an agent has found work in a work queue, the next steps in the workflow for executing a flow run are managed by the orchestration and execution layers of Prefect. Here's what typically happens: 1. When an agent queries and finds a flow run in the work queue, it's generally based on the flow's deployment specification, which tells the agent what to execute and how. This spec includes information about the specific flow to run, any flow parameters, and configuration like environment variables, secrets, or infrastructure requirements. 2. The agent will then take the necessary steps to spin up the execution environment, which could involve starting a container, a virtual machine, or submitting a job to a cloud service. 3. Once the execution environment is ready, the agent instructs it to start the flow run. The flow's code and configuration are used to ensure the correct version and flow are executed. In terms of how Prefect ensures that multiple agents do not pick up the same flow run, there is a mechanism in place to manage this kind of race condition. Generally, when an agent claims a flow run from the work queue, the orchestration layer will mark that flow run as being in progress or locked so that other agents know not to pick it up. This is usually managed through database transactions where the status of the flow run is updated atomically to prevent duplication of work. The locking mechanism ensures that even if multiple agents are polling the same queue, only one will successfully claim a particular flow run, and others will move on to look for other available work. This coordination is critical to ensure that each flow run is executed exactly once and maintains the integrity of the workflow. The documentation and discussions provided above give general guidance on migrating from agents to workers and on how Prefect handles race conditions when multiple agents could potentially execute the same flow run. Prefect's concurrency controls at the orchestration level are designed to prevent such scenarios, using internal locking mechanisms or transactional database operations.

@Marvin When agent queries for a job, does it do more than 1 select query?

According to the information sourced from the Prefect documentation and discussions, agents are lightweight polling services that retrieve scheduled work from a work pool and deploy the corresponding flow runs. The documentation does not explicitly mention the number of SQL select queries an agent performs when looking for a job. However, the agent's typical behavior is to poll for work at a regular interval, which is set to every 15 seconds by default. This interval is configurable with the

PREFECT_AGENT_QUERY_INTERVAL

setting. When an agent polls the work queue, it might procure all necessary information regarding available flow runs in a single SQL select query or multiple queries, depending on how the system is optimized for performance and concurrency controls. The agent's workflow might involve complex logic that includes not just query for available flow runs, but also for checking the status of the work pools, and updates to the status of flow runs after they are picked up, which could result in several interactions with the database. However, the specifics of how many SQL queries are executed during this process are not detailed in the publicly available excerpts. Given this information, it is possible that the agent may perform more than one select query for various reasons such as checking different conditions regarding flow run status, resource allocation, and other operational details, but this would be an implementation detail within the Prefect Core or the specific version of the Prefect agent you are using. If you need to know the exact number and nature of the queries, you would likely need access to the Prefect Core codebase or detailed logs from an actively running agent.

agents / workers talk to the API, where individual endpoints invoke the server side functions that use SQLAlchemy to perform the queries