AndreKR

Elasticsearch notes

Things named "explain"

Three things can be explained in elasticsearch:

Explain for each hit how its score was computed (Docs: Explain)

GET //_search?explain

AndreKR

@echo off

set PLINK_PATH=C:\Program Files (x86)\PuTTY\plink.exe
set WIRESHARK_PATH=C:\Program Files\Wireshark\Wireshark.exe

if "%1" == "" goto :usage

"%PLINK_PATH%" -ssh %1 "tcpdump -ni %2 -s 0 -w - not port 22" | "%WIRESHARK_PATH%" -k -i -
goto :end

AndreKR

To help you with the process of converting a MySQL app to PostgreSQL, I collected a list of differences between MySQL and PostgreSQL (PG).

Important changes:

* Strings are quoted with '...' or with $token$...$token$. Single-quotes are escaped with single-quotes.
* Identifiers are folded to lowercase, unless they are quoted with "..." which makes them case-sensitive
* The max identifier length is 63
* There are some system columns that cannot be used as an identifier (probably not a problem)
* Expressions are evaluated in arbitrary order, so WHERE x > 0 AND y/x > 1.5 can lead to a division by zero and has to be replaced with WHERE CASE WHEN y > 0 THEN y/x > 1.5 ELSE FALSE END
* SELECT CASE WHEN x > 0 THEN x ELSE 1/0 END would still lead to a division by zero because the constant 1/0 is evaluated even before the query starts

AndreKR

DROP TABLE IF EXISTS public.with_enum;
DROP TABLE IF EXISTS public.with_text;
DROP TYPE IF EXISTS my_enum;

CREATE TYPE public.my_enum AS ENUM ('axyzxyz', 'bxyzxyz', 'cxyzxyz', 'dxyzxyz');

CREATE TABLE public.with_enum (
  id serial NOT NULL PRIMARY KEY,
  blah integer,
  thecolumn my_enum

AndreKR

// Initialize an empty image
dest := image.NewRGBA(image.Rect(0, 0, 800, 300))

// Draw a white background
draw.Draw(dest, dest.Bounds(), &image.Uniform{color.White}, image.ZP, draw.Src)

// Read the font

fontBytes, err := ioutil.ReadFile(exeDir + "/DejaVuSans.ttf")
if err != nil {

AndreKR

func handleRequest(w http.ResponseWriter, r *http.Request) {

	cn := w.(http.CloseNotifier)
	cc := cn.CloseNotify()

	go func() {
		<-cc
		log.Println("Closed!")
	}()

AndreKR

package main

import (
	agwd "github.com/sclevine/agouti"
	tbwd "github.com/tebeka/selenium"
	"log"
	sgwd "sourcegraph.com/sourcegraph/go-selenium"
)

// Helper for sourcegraph/go-selenium

AndreKR

// (I prefer "Two channels wrapped" and "Anonymous struct" over the other two)

// Two channels
resultCh := make(chan Result)
errorCh := make(chan Result)

go func(resultCh chan Result, errorCh chan errpr) {
  errorCh <- errors.New("Does not compute")}
  resultCh <- result
}(resultCh, errorCh)

AndreKR

package main

// Trigger ensures a worker runs once after it has been triggered, no matter how many trigger events happened during
// its last run.
//
// Usage:
//   trigger := NewTrigger()
//   go func() {
//     for _ = range trigger {
//       do_work()

AndreKR

// While the Go documentation promotes the context package for keeping track of request context and cancelation, to
// actually use it for canceling work in http requests some plumbing is necessary:

// getCancelableContextFromResponseWriter gets a context.Context that is canceled when the client (browser) closes the connection
func getCancelableContextFromResponseWriter(w http.ResponseWriter) context.Context {

	// Create a context that can be handed down to the workers to relay cancellation
	ctx, cancelContext := context.WithCancel(context.Background())

	// Get a channel that receives a value when the request is canceled