getAllKeys returns an empty array on server 1.5+

[scara]

Here is a run of the same code against server 1.4 and 1.5:

# docker-compose up
Starting mdl60037_memcached15_1
Starting mdl60037_memcached14_1
Recreating mdl60037_runner_1
Attaching to mdl60037_memcached15_1, mdl60037_memcached14_1, mdl60037_runner_1
runner_1       | Running memcached extension 3.0.2 against memcached server 1.4.39 (memcached14)...
runner_1       | Expecting 'int' key on memcached14 to be: (int)99...
runner_1       | int(99)
runner_1       | Expecting all keys on memcached14 to be: 'int' => (int)99...
runner_1       | array(1) {
runner_1       |   [0]=>
runner_1       |   string(3) "int"
runner_1       | }
runner_1       | Running memcached extension 3.0.2 against memcached server 1.5.1 (memcached15)...
runner_1       | Expecting 'int' key on memcached15 to be: (int)99...
runner_1       | int(99)
runner_1       | Expecting all keys on memcached15 to be: 'int' => (int)99...
runner_1       | array(0) {
runner_1       | }
mdl60037_runner_1 exited with code 0

Find attached the code: MDL-60037.zip.

Matteo

[scara]

Not sure if related to #315.

[sodabrew]

Yeah, this looks exactly like the circumstances for #315 - the underlying libmemcached library will stop iterating the 2nd..nth servers once it hits the error from trying to fetch keys from the 64th slab.

[scara]

Hi @sodabrew,
the difference here is running the same code using only one server, first on 1.4x then on 1.5.x, to compare the results:

<?php

function run_test_suite($host)
{
    $extVersion = phpversion('memcached');

    $cache = new Memcached($host);
    $cache->addServer($host, 11211);
    $serverVersion = reset($cache->getVersion());
    echo "Running memcached extension $extVersion against memcached server $serverVersion ($host)...\n";

    $cache->set('int', 99);
    $key = $cache->get('int');
    echo "Expecting 'int' key on $host to be: (int)99...\n";
    var_dump($key);

    $keys = $cache->getAllKeys();
    echo "Expecting all keys on $host to be: 'int' => (int)99...\n";
    var_dump($keys);
}

// Wait 3s to be sure that memcached daemons are up&running.
sleep(3);

run_test_suite('memcached14');
run_test_suite('memcached15');

Should 1.5.x be supported the same as 1.4.x?

TIA,
Matteo

[scara]

Bumping...
@sodabrew, any advice?

[scara]

Bumping...
Pinging @sodabrew and @trondn to ask for thoughts about where this issue should be addressed.

TIA,
Matteo

[ZuZuD]

I was wondering what is the interest of such a method as it returns the keys in an inconsistent manner because based on "stats cachedump" ?

[sodabrew]

#315 implements a workaround for the underlying libmemcached library that made a hard-coded assumption of the number of buckets in the memcached server that changed from 1.4.x to 1.5.x.

There's no active maintainer for libmemcached at this time. I do wonder if it should get adopted by https://github.com/memcached /cc @memcached ?