the wonders of redis key value store series - day 2 - distributed... · the wonders of redis key...

The Wonders of Redis key-value store

Shashank Tiwariblog: shanky.org | twitter: @tshanky

st@treasuryofideas.com

Tuesday, January 25, 2011

List cmd: LINDEX

redis> lindex myList 1

"fourth_element"

redis> lrange myList 0 4

1) "seventh_element"

2) "fourth_element"

Tuesday, January 25, 2011

List cmd: LINSERT(BEFORE or AFTER)

redis> linsert myList before "fourth_element" eighth_element

(integer) 3

redis> lrange myList 0 4

1) "seventh_element"

2) "eighth_element"

3) "fourth_element"

Tuesday, January 25, 2011

List cmd: LSET(set element at index to value)

redis> lset myList 2 ninth_element

OK

redis> lrange myList 0 4

1) "seventh_element"

2) "eighth_element"

3) "ninth_element

Tuesday, January 25, 2011

List cmd: BLPOP, BRPOP

• Blocking counterparts of LPOP and RPOP

• BLPOP list1 list2 list2 <timeout>

• Blocked until lpush, rpush or timeout.

Tuesday, January 25, 2011

List cmd: BRPOPLPUSH

• Blocking version of RPOPLPUSH

• Blocked until lpush, rpush or timeout

Tuesday, January 25, 2011

Set Commands

Tuesday, January 25, 2011

Set cmd: SADD(element added only once)

• redis> sadd mySet first_element

• (integer) 1

• redis> sadd mySet first_element

• (integer) 0

Tuesday, January 25, 2011

Set cmd: SCARD(set cardinality)

redis> scard mySet

(integer) 1

Tuesday, January 25, 2011

Set cmd: SDIFF

redis> sadd set_1 a

(integer) 1

redis> sadd set_1 b

(integer) 1

redis> sadd set_2 a

(integer) 1

Tuesday, January 25, 2011

Set cmd: SDIFFSTORE

• SDIFF and store result to destination

Tuesday, January 25, 2011

Set cmd: SINTER

redis> sinter set_1 set_2

1) "a"

Tuesday, January 25, 2011

Set cmd: SINTERSTORE

• SINTER and store result to destination

Tuesday, January 25, 2011

Set cmd: SMEMBERS(list all)

redis> smembers set_3

1) "a"

Tuesday, January 25, 2011

Set cmd: SISMEMBER

redis> sismember set_3 "a"

(integer) 1

Tuesday, January 25, 2011

Set cmd: SPOP, SRANDMEMBER

redis> spop set_1

"a"

pops a random member

Tuesday, January 25, 2011

Set cmd: SREM

redis> srem set_1 "a"

(integer) 1

Tuesday, January 25, 2011

Set cmd: SMOVE(from source to destination)

redis> smembers set_1

1) "a"

2) "b"

redis> smove set_1 set_2 "a"

(integer) 1

Tuesday, January 25, 2011

Set cmd: SUNION

redis> smembers set_1

1) "b"

redis> smembers set_2

1) "a"

redis> sunion set_1 set_2

1) "a"

Tuesday, January 25, 2011

Set cmd: SUNIONSTORE

• SUNION and store result to destination

Tuesday, January 25, 2011

Sorted Set Commands

Tuesday, January 25, 2011

Sorted Set cmd:

• A set similar to that of the Set commands

• ZADD, ZCARD, ZRANGE, ZUNIONSTORE and more

• (not covered in this presentation)

Tuesday, January 25, 2011

Authentication

• Password protection

• redis.conf -- requirepass <password>

• AUTH <password>

• then commands

Tuesday, January 25, 2011

SELECT a db

redis> select 0

OK

redis> select 1

OK

new connection uses db 0

Tuesday, January 25, 2011

Redis Internal Storage

• Everything is stored as strings

• Even lists, sets, sorted sets and maps are composed of strings

Tuesday, January 25, 2011

Simple dynamic string (SDS)

• Special structure

• buff – a character array that stores the string

• len – a long type that stores the length of the buff array

• free – number of additional bytes available for use

Tuesday, January 25, 2011

Write to disk

• Everything resides in primary memory till its written to disk

• does not use mmap files

Tuesday, January 25, 2011

Why not memory mapped files?

• http://code.google.com/p/redis/wiki/VirtualMemorySpecification

• http://antirez.com/post/redis-virtual-memory-story.html

• swap pages and redis object don’t map one to one

• format in memory and disk are not same. Disk formats are compressed.

Tuesday, January 25, 2011

Master-slave

• Slave connects and sends SYNC command

• All database and commands relayed from master to slave

• For replication slave config -- slaveof <master ip> 6379

Tuesday, January 25, 2011