Valkey Basics

A key-value store keeps a value under a name, and gives it back when you ask for the name. Websites use one to remember a visitor's session or to count page views, because it answers in a fraction of a millisecond. Valkey is a free one that speaks the same commands as Redis. You will store and fetch a value, make a value expire, and meet a list, a hash and a counter.

This terminal has no Valkey client, so the first command makes a tiny one: a function called v that sends its words to the store on port 6379 with nc and prints what comes back. It prints nothing itself. Then SET stores a value under a key and the store answers +OK. GET asks for it: the reply is $5, the length of the answer, and on the next line hello.

EX 5 says this key lives for five seconds, and v TTL code in your own terminal prints how many seconds are left, if you are quick. Run the second command after about six seconds: the reply is $-1, the store's way of saying there is nothing there. That is how a login session is made to time out.

RPUSH adds to the end of a list and answers how long the list is now, :3. HSET stores named fields in one key, a hash, and answers how many it added, :2. INCR adds one to a number and answers the new value, :1: press it again for :2, and a thousand visitors at once would still be counted exactly. In your own terminal v LRANGE tasks 0 -1 reads the list back and v HGETALL user:1 the hash. A reply starting : is a number and $ a piece of text.

Press Stop the lab on the lab bar and then Start the lab again. The new terminal has forgotten v, so press step 1's first Run to make it again, then its v GET greeting Run: it is still hello, and code has long expired. Valkey keeps everything in memory, which is why it is fast, and logs each write to a file in a named volume, which the platform saves, so it can rebuild the memory when it starts. A store with no such file would start empty every time.