Kleppmann, Martin

Simple Log Analysis

Suppose you have a web server that appends a line to a log file every time it serves a request, e.g., using the nginx defaults (line breaks added for readability):

216.58.210.78 - - [27/Feb/2015:17:55:11 +0000] "GET /css/main.css HTTP/1.1"
200 3377 "http://foo.com/" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7)
AppleWebKit/537.36 (KHTML, like Gecko) Chrome/153.0.0.0 Safari/537.36"

To find the 5 most popular pages on your website, you can do:

Link to notes

Part I. Foundations of Data Systems

✅ Ch 01. Reliable, Scalable and Maintainable Applications:

• ✅ Thinking About Data Systems
• ✅ Reliability: hardware faults; software errors; human errors; importance of reliability.
• ✅ Scalability: describing load; describing performance; approaches for coping with load.
• ✅ Maintainability: operability - making life easy for operations; simplicity - managing complexity; evolvability - making change easy.

Ch 02. Data Models and Query Languages:

Query Languages for Data

If you have a list of animal species and you want to return only the sharks in the list, a relational algebra expression would be \( \text{sharks} = \sigma_{\text{family = “Sharks”}}(\text{animals}) \). SQL queries follow the structure of relational algebra closely:

SELECT * FROM animals WHERE family = 'Sharks';

… while an imperative query would be:

function getSharks() {
  let sharks = [];
  for (let i = 0; i < animals.length; i++) {
    if (animals[i].family === "Sharks") {
      sharks.push(animals[i]);
    }
  }
  return sharks;
}