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I am using rub redis gem. Wondering if I do for example:
redis.pipelined do
REDIS.del("users:#{current_user_id}:i-unread")
REDIS.lpush("users:#{current_user_id}:i-read", items)
REDIS.ltrim("users:#{current_user_id}:i-read", 0, Interaction::MAX_INTERACTIONS)
end
is this order of execution guaranteed?
447
Redis pipelining is a technique for improving performance by issuing multiple commands at once without waiting for the response to each individual command. Pipelining is supported by most Redis clients. This document describes the problem that pipelining is designed to solve and how pipelining works in Redis.
Redis Transactions make two important guarantees: All the commands in a transaction are serialized and executed sequentially.
Unlike pipelines, pipelines use special commands to mark the beginning and the end of the transaction, and the server also can queue the commands from a transaction (so the client can send one at a time). So transactions are stateful on the server, it actually keeps track of an ongoing transaction.
The multi command tells Redis to begin a transaction block. Any subsequent commands will be queued up until you run an exec command, which will execute them.
of course the order is guaranteed, otherwise pipelining would be useless. you can always look at the code. for example, this test clearly assumes that the commands are executed sequentially: https://github.com/redis/redis-rb/blob/master/test/pipelining_commands_test.rb#L32
def test_bulk_and_multi_bulk_commands_mixed
r.pipelined do
r.lpush "foo", "s1"
r.lpush "foo", "s2"
r.mset("baz", "s3", "qux", "s4")
end
assert_equal 2, r.llen("foo")
assert_equal "s2", r.lpop("foo")
assert_equal "s1", r.lpop("foo")
assert_equal "s3", r.get("baz")
assert_equal "s4", r.get("qux")
end
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