[BUG] eval is 150% slower than multiple commands in phpredis but not in redis-cli

[kkmuffme]

Expected behaviour

eval should be faster than running multiple commands separately and processing in PHP in between.

Actual behaviour

in CLI:

redis-cli SET mykey "HELLO;WORLD"
redis-cli SET HELLO "FOO"
redis-cli SET WORLD "BAR"

time for i in {1..1000}; do redis-cli MGET $(redis-cli GET mykey | sed -E 's/^([^;]+);(.+)$/\1 \2/') > /dev/null; done
time for i in {1..1000}; do redis-cli EVAL 'local value = redis.call( "GET", KEYS[1] ); local a, b = value:match( "^([^;]+);(.+)$" ); return redis.call( "MGET", a, b )' 1 mykey > /dev/null; done

EVAL is about 100% faster than running multiple commands (I used the inefficient "sed" on purpose to ensure it's not the regex causing it, using a more efficient sed 's/;/ /' delivers the same results though)

In PHP the opposite is true though and eval is about 150% slower:
(same issue for evalSha/evalSha_ro and eval_ro, even though those are slightly faster than eval, still much slower)

$x = 0;
$start = microtime( true );
while ( $x < 1000 ) {
	$redis->eval( 'local value = redis.call( "GET", KEYS[1] ); local a, b = value:match( "^([^;]+);(.+)$" ); return redis.call( "MGET", a, b )', [ 'mykey' ], 1 );
	$x++;
}
var_dump( microtime( true ) - $start );

$x = 0;
$start = microtime( true );
while ( $x < 1000 ) {
	$r = $redis->get( 'mykey' );
	$redis->mGet( explode( ';', $r, 2 ) );
	$x++;
}
var_dump( microtime( true ) - $start );

I'm seeing this behaviour on

• OS: unix
• Redis: 7.2.5
• PHP: 8.3.x
• phpredis: 6.0.2

I've checked

• There is no similar issue from other users
• Issue isn't fixed in develop branch

[michael-grunder]

I'm guessing the overhead of invoking redis-cli over and over again is adding a huge amount of noise to the benchmark. Specifically, the non-lua invocation executes it twice per loop:

time for i in {1..1000}; do redis-cli MGET $(redis-cli GET mykey | sed -E 's/^([^;]+);(.+)$/\1 \2/') > /dev/null; done

Also I get the opposite result running your snippet (that I modified slightly).

<?php

function printTiming($what, $n, $tm) {
    printf("Executed %s '%s' calls in %2.6f sec (%s/sec)\n",
           number_format($n), $what, $tm,
           number_format($n / $tm));
}

$redis = new Redis;
$redis->connect('localhost', 6379);
$redis->set('mykey', 'HELLO;WORLD');
$redis->set('HELLO', 'FOO');
$redis->set('WORLD', 'BAR');

define('RUNS', 10000);

define('SCRIPT', 'local value = redis.call( "GET", KEYS[1] ); local a, b = value:match( "^([^;]+);(.+)$" ); return redis.call( "MGET", a, b )');

$sha = $redis->script('load', SCRIPT);

$start = microtime( true );
for ($i = 0; $i < RUNS; $i++) {
    $redis->evalSha($sha, [ 'mykey' ], 1 );
}
printTiming('EVALSHA', RUNS, microtime(true) - $start);

$start = microtime( true );
for ($i = 0; $i < RUNS; $i++) {
    $r = $redis->get( 'mykey' );
    $redis->mget(explode(';', $r, 2));
}

printTiming('GET/MGET', RUNS, microtime(true) - $start);

Lua is faster on my machine, by quite a bit:

On a Ryzen 1800X (x86-64):

$ php test.php
Executed 10,000 'EVALSHA' calls in 0.747971 sec (13,370/sec)
Executed 10,000 'GET/MGET' calls in 1.169543 sec (8,550/sec)

On an M1 (arm):

$ php test.php
Executed 10,000 'EVALSHA' calls in 0.234423 sec (42,658/sec)
Executed 10,000 'GET/MGET' calls in 0.365942 sec (27,327/sec)

[kkmuffme]

I tested it again now - on the same server, however with much less load than yesterday, and don't see the issue anymore either.

Will update if I'm able to figure out what exactly caused this