A (highly opinionated) distributed job-queue built specifically for defering and executing heavy SQL read jobs asynchronously
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README.md

SQL Jobber

CircleCI (all branches)

This is a highly experimental alpha version. Use with care.

A highly opinionated, distributed job-queue built specifically for defering and executing SQL read query jobs.

  • Standalone server that exposes HTTP APIs for managing jobs and groups of jobs (list, post, status check, cancel jobs)
  • Reads SQL queries from .sql files and registers them as jobs ready to be queued
  • Supports MySQL and PostgreSQL as data sources for tasks
  • Supports MySQL and PostgreSQL as result stores for task responses
  • Written in Go and built on top of Machinery. Supports multi-process, multi-threaded, asynchronous distributed job queueing via a common broker backend (Redis, AMQP etc.)

Why?

Usecase 1

Consider an application that has a very large SQL database. When there are several thousand concurrent users requesting reports from the database simultaneously, every second of IO delay in query execution locks up the application's threads, snowballing and overloading the application. Instead, we defer every single report request into a job queue, there by immediately freeing up the front end application. The reports are presented to users as they're executed (frontend polls the job's status and prevents the user from sending any more queries). Fixed SQL Jobber servers and worker threads also act as traffic control and prevent the primary database from being indundated with requests.

Usecase 2

Once the reports are generated, it's only natural for users to further transform the results by slicing, sorting and filtering, generating additional queries to the primary database. To offset this load, these subsequent queries can be sent to a smaller, much faster database where the results of the original read query jobs are stored. These results are of course ephemeral and can be thrown away or expired.

sql-job-server png

Concepts

Task

A task is a named SQL job is loaded into the server on startup. Tasks are defined in .sql files in the simple goyesql format. Such queries are self-contained and produce the desired final output with neatly named columns. They can take arbitrary positional arguments for execution. A task can be attached to one or more specific databases defined in the configuration using the -- db: tag. In case of multiple databases, the query will be executed against a random one from the list. A -- queue: tag to always route the task to a particular queue, unless it's overriden by the queue param when making a job request. A -- results: tag specifies the results backend to which the results of a task will be written. If there are multiple result backends specified, the results are written a random one.

Example:

-- queries.sql

-- name: get_profit_summary
SELECT SUM(amount) AS total, entry_date FROM entries GROUP BY entry_date WHERE user_id = ?;

-- name: get_profit_entries
-- db: db0, other_db
-- queue: myqueue
-- results: my_res_db
SELECT * FROM entries WHERE user_id = ?;

-- name: get_profit_entries_by_date
SELECT * FROM entries WHERE user_id = ? AND timestamp > ? and timestamp < ?;

-- name: get_profit_entries_by_date
-- raw: 1
-- This query will not be prepared (raw=1)
SELECT * FROM entries WHERE user_id = ? AND timestamp > ? and timestamp < ?;

Here, when the server starts, the queries get_profit_summary and get_profit_entries are registered automatically as tasks. Internally, the server validates and prepares these SQL statements (unless raw: 1). ? are MySQL value placholders. For Postgres, the placeholders are $1, $2 ...

Job

A job is an instance of a named task that has been queued to run. Each job has an ID that can be used to track its status. If an ID is not passed explicitly, it is generated internally and returned. These IDs need not be unique, but only a single job with a certain ID can run at any given point. For the next job with the same ID to be scheduled, the previous job has to finish execution. Using non-unique IDs like this is useful in cases where users can be prevented from sending multiple requests for the same reports, like in our usecases.

Results

The results from an SQL query job are written to a result backend (MySQL or Postgres) from where they can be further read or queried. This is configured in the configuration file. The results from a job are written to a new table named after that job, where schema of the results table is automatically generated from the results of the original SQL query. All fields are transformed into one of these types BIGINT, DECIMAL, TIMESTAMP, DATE, BOOLEAN, TEXT.

Installation

1) Install

A pre-compiled binary can be downloaded from the releases page.

or:

go get github.com/knadh/sql-jobber to install the binary sql-jobber in $GOPATH/bin.

2) Configure

Copy the config.toml.sample file as config.toml somewhere and edit the configuration values.

3) Setup tasks

Write your SQL query tasks in .sql files in the goyesql format (as shown in the examples earlier) and put them in a directory somewhere.

4) Start the server

sql-jobber --config /path/to/config.toml --sql-directory /path/to/your/sql/queries

# Run 'sql-jobber --help' to see all supported arguments

Starting the server runs a set of workers listening on a default job queue. It also starts an HTTP service on http://127.0.0.1:6060 which is the control interface. It's possible to run the server without the HTTP interface by passing the --worker-only flag.

Usage

Method URI
GET /tasks Returns the list of registered SQL tasks
POST /tasks/{taskName}/jobs Schedules a job for a given task
GET /jobs/{jobID} Returns the status of a given job
GET /jobs/queue/{queue} Returns the list of all pending jobs in a queue
POST /groups Schedule a group of jobs
GET /groups/{groupID} Get the status of a job group and its jobs
DELETE /jobs/{jobID} Deletes a pending job from the queue and immediately cancels its execution and frees the thread. Only the Go PostgreSQL driver cancels queries mid execution. MySQL server will keep continuing to execute the query. For MySQL, it's important to set max_execution_time

POST requests accept raw JSON bodies. The JSON params are listed below.

Job param
job_id string (Optional) Alphanumeric ID for the job. Can be non-unique. If this is not passed, the server generates and returns one
queue string (Optional) Queue to send the job to. Only workers listening on this queue will receive the jobs.
eta string (Optional) Timestamp (yyyy-mm-dd hh:mm:ss) at which the job should start. If this is not provided, the job is queued immediately.
retries int (Optional) The number of times a failed job should be retried. Default is 0
ttl int (Optional) TTL for the results in the results backend for this particular job. This is NOT supported by the default SQL DB result backend
args[] []string (Optional) The positional argument to pass to the SQL query in the task being executed. This can be passed multiple times, one for each argument
Group param
group_id string (Optional) Alphanumeric ID for the group of jobs. Can be non-unique. If this is not passed, the server generates and returns one
concurrency int (Optional) Number of jobs to run concurrently in the group
Schedule a job
$ curl localhost:6060/tasks/get_profit_entries_by_date/jobs -H "Content-Type: application/json" -X POST --data '{"job_id": "myjob", "args": ["USER1", "2017-12-01", "2017-01-01"]}'

{"status":"success","data":{"job_id":"myjob","task_name":"get_profit_entries_by_date","queue":"sqljob_queue","eta":null,"retries":0}}
Schedule a group of jobs

Sometimes, it's necessary to schedule a group of jobs and perform an action once they're all complete. Group jobs here run concurrently and independent of each other. The group state can be polled to figure out if all the jobs in it have finished executing.

$ curl localhost:6060/groups -H "Content-Type: application/json" -X POST --data '{"group_id": "mygroup", "concurrency": 3, "jobs": [{"job_id": "myjob", "task": "get_profit_entries_by_date", "args": ["USER1", "2017-12-01", "2017-01-01"]}, {"job_id": "myjob2", "task": "get_profit_entries_by_date", "args": ["USER1", "2017-12-01", "2017-01-01"]}]'

{"status":"success","data":{"group_id":"mygroup","jobs":[{"job_id":"myjob","task":"test1","queue":"sqljob_queue","eta":null,"retries":0},{"job_id":"myjob2","task":"test2","queue":"sqljob_queue","eta":null,"retries":0}]}}
Check a job's status
$ curl localhost:6060/jobs/myjob
{"status":"success","data":{"job_id":"myjob","status":"SUCCESS","results":[{"Type":"int64","Value":2}],"error":""}}~                                                                               

# `Results` indicates the number of rows generated by the query.

Advanced usage

Multiple queues, workers, and job distribution

It's possible to run multiple workers on one or more machines that run different jobs with different concurrency levels independently of each other using different queues. Not all of these instances need to expose the HTTP service and can run as --worker-only. This doesn't really make a difference as long as all instances connect to the same broker backend. A job posted to any instance will be routed correctly to the right instances based on the queue parameter.

Often times, different queries have different priorities of execution. Some may need to return results faster than others. The below example shows two SQL Jobber servers being run, one with 30 workers and one with just 5 to process jobs of different priorities.

# Run the primary worker + HTTP control interface
sql-jobber --config /path/to/config.toml --sql-directory /path/to/sql/dir \
	--queue "high_priority" \
    --worker-name "high_priority_worker" \
    --worker-concurrency 30

# Run another worker on a different queue to handle low priority jobs
sql-jobber --config /path/to/config.toml --sql-directory /path/to/sql/dir \
	--queue "low_priority" \
    --worker-name "low_priority_worker" \
    --worker-concurrency 5 \
    --worker-only

# Send a job to the high priority queue.
$ curl localhost:6060/tasks/get_profit_entries_by_date/jobs -H "Content-Type: application/json" --data '{"job_id": "myjob", "queue": "high_priority", "args": ["USER1", "2017-12-01", "2017-01-01"]}'

# Send another job to the low priority queue.
$ curl localhost:6060/tasks/get_profit_entries_by_date/jobs -H "Content-Type: application/json" --data '{"job_id": "myjob", "queue": "low_priority"}'

Running tests locally

Copy test config.

cp ./.circleci/config.toml ./config_test.toml

Modify config file so that database dsn(s), redis addresses matches local setup.

go test -v ./... --config ./config_test.toml

License

Licensed under the MIT License.