get/getMulti return RES_NOTFOUND after buffered increment with result RES_UNKNOWN_READ_FAILURE with OPT_BINARY_PROTOCOL

[degtyaryov]

Hello!

Code:

<?php

$key = 'KEY';
$value = 'VALUE';

$memcached = new Memcached();

$memcached->addServer('127.0.0.1', '11211', 1);

$memcached->setOption( Memcached::OPT_BINARY_PROTOCOL, true);

$memcached->setOption(Memcached::OPT_BUFFER_WRITES, true);
$memcached->setOption(Memcached::OPT_NOREPLY, true);

$memcached->set($key, $value);
echo 'increment ', $key, ' ', $memcached->increment($key, 1, 1, 600), ' ', $memcached->getResultMessage(), "\n";
echo 'get ', $key, ' ', $memcached->get($key), ' ', $memcached->getResultMessage(), "\n";

Expect:

increment KEY  SUCCESS
get KEY VALUE SUCCESS

Result:

increment KEY  SUCCESS
get KEY  NOT FOUND

libmemcached send request 1 TCP package for set, incr and get

server memcached return 1 TCP package with 2 results:

• for incr return "Non-numeric server-side value for incr or decr"
• for get return "VALUE"

But php-memcached for get return NOT FOUND

Text protocol:

<?php

$key = 'KEY';
$value = 'VALUE';

$memcached = new Memcached();

$memcached->addServer('127.0.0.1', '11211', 1);


$memcached->setOption(Memcached::OPT_BUFFER_WRITES, true);
$memcached->setOption(Memcached::OPT_NOREPLY, true);

$memcached->set($key, $value);
echo 'increment ', $key, ' ', $memcached->increment($key, 1), ' ', $memcached->getResultMessage(), "\n";
echo 'get ', $key, ' ', $memcached->get($key), ' ', $memcached->getResultMessage(), "\n";

Expect:

increment KEY  SUCCESS
get KEY VALUE SUCCESS

Result:

increment KEY  SUCCESS
get KEY VALUE SUCCESS

libmemcached send request 1 TCP package for incr and get

server memcached return 1 TCP package with 1 results:

• for get return "VALUE"

[sodabrew]

Thank you for the minimal repro!

This is most likely a library issue rather than the php plugin code.

What version of libmemcache are you using? Try libmemcache-awesome for more recent updates and bug fixes.

[degtyaryov]

I tested this example on:

• Fedora 37
• PHP 8.2.11
• php-memcached 3.2.0
• libmemcached-awesome 1.1.3
• memcached-1.4.39 on Fedora 25

I checked it in C language

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <libmemcached/memcached.h>

int main(int argc, char *argv[])
{
    char *key= "KEY";
    char *value= "VALUE";

    memcached_server_st *servers = NULL;
    memcached_st *memc;
    memcached_return rc;
    
    uint64_t incr = UINT64_MAX;
    size_t key_length = strlen(key);

    char return_key[MEMCACHED_MAX_KEY];
    size_t return_key_length;
    char *return_value;
    size_t return_value_length;
    uint32_t flags;
    
    
    const char* keys[] = {key};
    size_t keys_length[] = {key_length};
    
    memcached_server_st *memcached_servers_parse (const char *server_strings);

    memc= memcached_create(NULL);
    
    servers= memcached_server_list_append(servers, "127.0.0.1", 11211, &rc);
    rc= memcached_server_push(memc, servers);
    
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_BINARY_PROTOCOL, 1);
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_NO_BLOCK, 1);
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_BUFFER_REQUESTS, 1);
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_NOREPLY, 1);

   
    rc= memcached_set(memc, key, key_length, value, strlen(value), (time_t)0, (uint32_t)0);
    rc = memcached_increment_with_initial(memc, key, key_length, 1, 1, (time_t)600, &incr);

    rc = memcached_mget(memc, keys, keys_length, 1);
    
    return_value = memcached_fetch(memc, return_key, &return_key_length, &return_value_length, &flags, &rc);
    fprintf(stdout,"Value: %s\n",return_value);
    
    return_value = memcached_fetch(memc, return_key, &return_key_length, &return_value_length, &flags, &rc);
    fprintf(stdout,"Value: %s\n",return_value);

    memcached_quit(memc);
    
    return 0;
}

Expect:

Value: VALUE

Result:

Value: (null)

libmemcached send request 1 TCP package for set, incr and get

server memcached return 1 TCP package with 2 results:

• for incr return "Non-numeric server-side value for incr or decr"
• for get return "VALUE"

I checked it in C language on Fedora 39 with libmemcached-awesome 1.1.4 memcached-1.6.21
Result:

Value: (null)

libmemcached send request 2 TCP package:

• for set and incr
• for get

server memcached return 1 TCP package with 2 results:

• for incr return "Non-numeric server-side value for incr or decr"
• for get return "VALUE"

[degtyaryov]

Another example:

<?php

$key1 = 'KEY1';
$key2 = 'KEY2';

$value1 = 'VALUE1';
$value2 = 'VALUE2';

$memcached = new Memcached();

$memcached->addServer('127.0.0.1', '11212', 1);

$memcached->setOption( Memcached::OPT_BINARY_PROTOCOL, true);

$memcached->set($key1, $value1);

$memcached->setOption(Memcached::OPT_BUFFER_WRITES, true);
$memcached->setOption(Memcached::OPT_NOREPLY, true);

for ($i = 0; $i < 100; ++$i) {
        $memcached->delete($key2);
}
echo 'get ', $key1, ' ', $memcached->get($key1), ' ', $memcached->getResultMessage(), "\n";

Expect:

get KEY1 VALUE1 SUCCESS

Result:

get KEY1 VALUE1 SUCCESS

Next execute result random:

get KEY1  NOT FOUND

C Language:

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <libmemcached/memcached.h>

int main(int argc, char *argv[])
{
    char *key1= "KEY1";
    char *value1= "VALUE1";
    
    char *key2= "KEY2";
    char *value2= "VALUE2";

    memcached_server_st *servers = NULL;
    memcached_st *memc;
    memcached_return rc;
    
    size_t key1_length = strlen(key1);
    size_t key2_length = strlen(key2);

    char *return_value;
    size_t return_value_length;
    uint32_t flags;
    
    memcached_server_st *memcached_servers_parse (const char *server_strings);

    memc= memcached_create(NULL);
    
    servers= memcached_server_list_append(servers, "127.0.0.1", 11211, &rc);
    rc= memcached_server_push(memc, servers);
    
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_BINARY_PROTOCOL, 1);
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_NO_BLOCK, 1);
    
    rc= memcached_set(memc, key1, key1_length, value1, strlen(value1), (time_t)0, (uint32_t)0);
    
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_BUFFER_REQUESTS, 1);
    memcached_behavior_set(memc, MEMCACHED_BEHAVIOR_NOREPLY, 1);

    for (int i = 0; i < 100; ++i) {
        rc= memcached_delete(memc, key2, key2_length, (time_t)0);
    }

    return_value = memcached_get(memc, key1, key1_length, &return_value_length, &flags, &rc);
    fprintf(stdout,"Value: %s\n",return_value);

Expect:

Value: VALUE1

Result:

Value: (null)

Memcached to delete a non-existent key sometimes returns a response.

Memcache Protocol, Delete Quietly Response
    Magic: Response (129)
    Opcode: Delete Quietly (20)
    Key Length: 0
    Extras length: 0
    Data type: Raw bytes (0)
    Status: Key not found (1)
        [Expert Info (Note/Response): Delete Quietly: Key not found]
            [Delete Quietly: Key not found]
            [Severity level: Note]
            [Group: Response]
    [Value length: 9]
    Total body length: 9
    Opaque: 1835008
    CAS: 0
    Value: Not found

Sometimes there is no answer.

Questions:

1. Why does the memcached server send responses and generate unnecessary network traffic? After all, the absence of a key is not an error. Why out of 100 requests there are only 30 answers?
2. Why does the libmemcached discard everything received after such a response?