what is the correct syntax of BLPOP on Predis?

[geocine]

I do it like this:

$r = new Predis\Client($single_server, $options);
$retval = $r->blpop('queue:query');

But I get this error:

ERR wrong number of arguments for 'blpop' command

Whenever I do this

$r = new Predis\Client($single_server, $options);
$retval = $r->blpop('queue:query',0);

I get the error:

Error while reading line from the server

Doing it from redis-cli

redis 127.0.0.1:6379> BLPOP queue:query
(error) ERR wrong number of arguments for 'blpop' command
redis 127.0.0.1:6379> BLPOP queue:query 0
1) "queue:query"
2) "hello world"

[nrk]

The second one, that is $r->blpop('queue:query',0);, is correct, but 0 as a value for the timeout argument blocks indefinitely until a message is available in the queue. If you really want to wait forever for a message using BLPOP then you have to configure Redis to not close idle clients after 300 seconds (you can do this by editing your redis.conf and setting the timeout entry to 0) and add read_write_timeout => 0 to the server parameters array / string passed to the constructor of Predis\Client.

This is the common cause for such an error using BLPOP, but if it's something different than you should tell me:

• your version of Redis
• you version of PHP
• on which OS platform you are running

[geocine]

I was pushing to a different database which is the default 0 . I used predis example which uses database 15. After I pushed data to 15. This error vanished Error while reading line from the server.

Thank you for the very detailed explanation.