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@dvirsky
dvirsky / gist:f9ebf6f66f763a356d4a
Created November 19, 2014 11:58
Long running Python Parent/Child communication via pipes
View gist:f9ebf6f66f763a356d4a
import subprocess
import time
import sys
def parent():
p = subprocess.Popen(['python', './testp.py', '--child'], stdin=subprocess.PIPE, stdout=subprocess.PIPE)
@dvirsky
dvirsky / gist:dfdfd4066c70e8391dc5
Created December 24, 2014 13:45
Checking is a function was deferred or not
View gist:dfdfd4066c70e8391dc5
package main
import(
"fmt"
"runtime"
"io/ioutil"
"bytes"
"strings"
)
View gist:16411e335531aef6c5bf
package redis
import (
"fmt"
"github.com/garyburd/redigo/redis"
)
// Batch represents a set of batched results, either a transaction or just send/receive.
//
@dvirsky
dvirsky / README.md
Last active August 29, 2015 14:20 — forked from jonhoo/README.md
View README.md

Distributed Read-Write Mutex in Go

The default Go implementation of sync.RWMutex does not scale well to multiple cores, as all readers contend on the same memory location when they all try to atomically increment it. This gist explores an n-way RWMutex, also known as a "big reader" lock, which gives each CPU core its own RWMutex. Readers take only a read lock local to their core, whereas writers must take all locks in order.

@dvirsky
dvirsky / disque_example.go
Created May 3, 2015 13:32
Disque Usage example
View disque_example.go
package main
import(
"fmt"
"time"
"github.com/EverythingMe/go-disque/disque"
"github.com/garyburd/redigo/redis"
)
View filter.go
package main
import (
"fmt"
"github.com/EverythingMe/inbloom/go/inbloom"
"net/http"
)
var vocabulary = []string{"foo", "bar", "baz", "hey", "yo", "go"}
View foo_test.go
package foo
import (
"testing"
)
type Foo struct {
a string
b int
c float32
View module.md

Creating a redis Module in 15 lines of code!

A quick guide to write a very very simple "ECHO" style module to redis and load it. It's not really useful of course, but the idea is to illustrate how little boilerplate it takes.

Step 1: open your favorite editor and write/paste the following code in a file called module.c

#include "redismodule.h"
/* ECHO <string> - Echo back a string sent from the client */
int EchoCommand(RedisModuleCtx *ctx, RedisModuleString **argv, int argc) {
View serialization.c
// A serializer prototype - you serialize by calling Write N times.
// the key type is determined on registration so not needed here
// the list size will be determined by redis when you exit, based on the number of times you called write()
int (*Serialize)(RedisModuleCtx *ctx, RedisModuleObjectWriter *out, RedisModuleKey *k)
// you deserialize by calling Read and reading one object at a time.
// numElements is passed so the user can preallocate stuff in advance
int (*Deserialize)(RedisModuleCtx *ctx, RedisModuleObjectReader *in, RedisModuleString *keyName, size_t numElements)
@dvirsky
dvirsky / RQL.md
Last active December 20, 2017 13:00
Proposed Secondary Index API and Query Language
View RQL.md

Proposed Redis Secondary Index Module API

What's This?

Redis is a very sophisticated data structure server, that can be used as a powerful in-memory database. However, if you look at redis as database per-se, it only has primary keys. There is no native way to ask redis for something like "what are the names of users over 18 who have visited my website yesterday?".

If you're familiar with traditional relational databases, this is usually done by creating an index on the relevant columns in your table, allowing to efficiently add complex WHERE clauses to your query. Such an index is called a Secondary Index.

While it is possible (and done by many many people) to implement these indexes on top of redis manually, doing them right and in a performant way is hard.