qlog is a microservice that functions as an implementation of tail for ASCII files accessible to the service.

qlog is a Java application using the Micronaut framework; Accordingly, we'll need to set up a few dependencies to get started.

1. Install SDKMAN!

   curl -s "https://get.sdkman.io" | bash
   source "$HOME/.sdkman/bin/sdkman-init.sh" # setup your shell for SDKMAN!

2. In the root directory of the project:

   sdk env install

   This will install the dependencies required to build and run the service. (Namely, the correct version of JDK.)

After the dependencies are installed build the project:

./gradlew build

This will initialize a new Gradle daemon and fetch the required dependencies from Maven Central repository and then build the project, including running the unit tests.

Run the service directly with Gradle:

./gradlew run

Gradle will use the compiled JAR (from the build step) and run it. You can confirm the service is up when your shell prints:

Startup completed in 294ms. Server Running: http://localhost:8080

You may also run the service using Docker.

First, build the Docker image:

./gradlew docker && docker build ./build/docker/main -t qlog

Then run the container:

docker run -d -p 8080:8080 -v /var/log:/var/log --name qlog qlog

The source of the volume can be any directory on your system. The service will read from files relative to /var/log within the container.

python3 ./scripts/genlog.py && sudo mv ./access.log /var/log/access.log

Generates a simulated Apache access log file that is ~2GB in size. You can use this file to query against the API or you can use any file you may already have or want to place in /var/log on your system.

The service serves a single endpoint: queryLog that returns a JSON object containing data field with an array of strings corresponding to the lines in the file. The endpoint will tail that service and return the last n lines of the file. Lines are returned as if tail -r was used, so the last line of the file is the first item in the array.

Query for lines from a file using curl:

curl -Ss "localhost:8080/queryLog?relativePath=access.log" | jq .

The service supports a trio of query params:

1. relativePath - Required, the file path relative to /var/log accessible to the service. This is the file that will be tailed by the service.
2. lineCount - Optional, default 42, the number of lines to return.
3. filter - Optional, default no op, the service will filter lines in the result set based on substring matching of the text in this filter against the line in the file.

Query parameter values must be URL encoded.

curl -Ss "localhost:8080/queryLog?relativePath=access.log&count=10&filter=DELETE%20%2Fscript.js" | jq .

If you're feeling spunky you can benchmark the service with ab: ApacheBench.

Hardware Used for below benchmark:

MacBook Pro M1 Max, 10-Core (8 performance + 2 efficiency), 64GB RAM, 4TB SSD.

ab -c 8 -n 10000 "http://localhost:8080/queryLog?relativePath=access.log&count=100&filter=%20200%20"
This is ApacheBench, Version 2.3 <$Revision: 1903618 $>
Copyright 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Licensed to The Apache Software Foundation, http://www.apache.org/

Benchmarking localhost (be patient)
Completed 1000 requests
Completed 2000 requests
Completed 3000 requests
Completed 4000 requests
Completed 5000 requests
Completed 6000 requests
Completed 7000 requests
Completed 8000 requests
Completed 9000 requests
Completed 10000 requests
Finished 10000 requests


Server Software:
Server Hostname:        localhost
Server Port:            8080

Document Path:          /queryLog?relativePath=access.log&count=100&filter=%20200%20
Document Length:        20674 bytes

Concurrency Level:      8
Time taken for tests:   3.667 seconds
Complete requests:      10000
Failed requests:        0
Total transferred:      207850000 bytes
HTML transferred:       206740000 bytes
Requests per second:    2727.22 [#/sec] (mean)
Time per request:       2.933 [ms] (mean)
Time per request:       0.367 [ms] (mean, across all concurrent requests)
Transfer rate:          55356.72 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.3      0       7
Processing:     2    3  15.3      2     539
Waiting:        1    2  15.3      2     539
Total:          2    3  15.3      2     539

Percentage of the requests served within a certain time (ms)
  50%      2
  66%      2
  75%      3
  80%      3
  90%      3
  95%      4
  98%      5
  99%      6
 100%    539 (longest request)

Tune the concurrency (-c), the total number of requests (-n), and the target URL to get a clear understanding of the performance characteristics of the service.