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chore: note it is safe to auto-reconnect #126

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chore: note it is safe to auto-reconnect #126

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3 changes: 3 additions & 0 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,9 @@ Redlock works with Redis versions 6.0 or later.

Redlock >= 2.0 only works with `RedisClient` instance.

If you'd like to enable auto-reconnect attempts like in Redis 5,
be sure to instantiate a RedisClient with `reconnect_attempts: 1`.
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@bf4 bf4 Feb 17, 2023 •
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aside, interesting logic inside sidekiq where it defines redis(&block) https://github.com/sidekiq/sidekiq/blob/v7.0.5/lib/sidekiq/config.rb#L118-L133

    def redis
      raise ArgumentError, "requires a block" unless block_given?
      redis_pool.with do |conn|
        retryable = true
        begin
          yield conn
        rescue RedisClientAdapter::BaseError => ex
          # 2550 Failover can cause the server to become a replica, need
          # to disconnect and reopen the socket to get back to the primary.
          # 4495 Use the same logic if we have a "Not enough replicas" error from the primary
          # 4985 Use the same logic when a blocking command is force-unblocked
          # The same retry logic is also used in client.rb
          if retryable && ex.message =~ /READONLY|NOREPLICAS|UNBLOCKED/
            conn.close
            retryable = false
            retry
          end
          raise
        end
      end
    end

I'm doing some more comparisons since we got a flood of OpenSSL errors for about 10 minutes today which Heroku https://help.heroku.com/70UD7VSR/why-am-i-seeing-syscall-returned-5-errno-0-state-sslv3-tls-write-client-hello-when-trying-to-connect-to-heroku-redis reports as "because the maximum number of clients to Redis has been reached" which appears to be what happened
image

Nothing this PR would address, I don't think, but worth sharing in the upgrade changes discussion, I think.


## Installation

Add this line to your application's Gemfile:
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8 changes: 6 additions & 2 deletions lib/redlock/client.rb
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Expand Up @@ -169,15 +169,17 @@ def initialize(connection)
def lock(resource, val, ttl, allow_new_lock)
recover_from_script_flush do
@redis.with { |conn|
conn.call('EVALSHA', Scripts::LOCK_SCRIPT_SHA, 1, resource, val, ttl, allow_new_lock)
# NOTE: is not idempotent and unsafe to retry
conn.call_once('EVALSHA', Scripts::LOCK_SCRIPT_SHA, 1, resource, val, ttl, allow_new_lock)
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I assume you mean unsafe if you're using call_once?

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ah, comment got out of date with my code. I changed my mind that locking probably isn't idempotent and change the code from call to call_once didn't update the comment.

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@bf4 bf4 Feb 17, 2023 •
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now the logic and comments are in sync

unlock/lock

# NOTE: is not idempotent and unsafe to retry
conn.call_once(...)

load_scripts/get remaining ttl

# NOTE: is idempotent and safe to retry
conn.call(...)

}
end
end

def unlock(resource, val)
recover_from_script_flush do
@redis.with { |conn|
conn.call('EVALSHA', Scripts::UNLOCK_SCRIPT_SHA, 1, resource, val)
# NOTE: is not idempotent and unsafe to retry
conn.call_once('EVALSHA', Scripts::UNLOCK_SCRIPT_SHA, 1, resource, val)
}
end
rescue
Expand All @@ -187,6 +189,7 @@ def unlock(resource, val)
def get_remaining_ttl(resource)
recover_from_script_flush do
@redis.with { |conn|
# NOTE: is idempotent and safe to retry
conn.call('EVALSHA', Scripts::PTTL_SCRIPT_SHA, 1, resource)
}
end
Expand All @@ -205,6 +208,7 @@ def load_scripts

@redis.with do |connnection|
scripts.each do |script|
# NOTE: is idempotent and safe to retry
connnection.call('SCRIPT', 'LOAD', script)
end
end
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