Unknown return code

[tmm1]

I'm seeing occasional Memcached::Error with strange return code values:

Unknown return code: 10234
Unknown return code: 51194
Unknown return code: 63482
Unknown return code: 34810
Unknown return code: 55290
Unknown return code: 26640
Unknown return code: 41872

AFAIK, these are all invalid values since Memcached::Lib::MEMCACHED_MAXIMUM_RETURN is 40

[tmm1]

All the exceptions are from https://github.com/evan/memcached/blob/master/lib/memcached/memcached.rb#L504

ruby/1.8/gems/memcached-1.4.2/lib/memcached/memcached.rb:621:in `reraise'
ruby/1.8/gems/memcached-1.4.2/lib/memcached/memcached.rb:598:in `check_return_code'
ruby/1.8/gems/memcached-1.4.2/lib/memcached/memcached.rb:504:in `get_orig'
ruby/1.8/gems/memcached-1.4.2/lib/memcached/rails.rb:81:in `get_multi'

[evan]

Very curious, but I need a reproducible test case to do anything about it.

[tmm1]

Found another reference at http://stackoverflow.com/questions/13212516/what-does-the-memcached-return-code-44120-mean

It appears this occurs when poll() times out, since memcached_fetch_result never sets a value for memcached_return *error.

This was fixed upstream by detecting the timeout and setting MEMCACHED_NOTFOUND or MEMCACHED_END accordingly.

[evan]

Nice find. Can you backport the fix?

[tmm1]

I think this should work, but hard to be sure since so much has changed upstream.

diff --git a/ext/libmemcached-0.32/libmemcached/memcached_fetch.c b/ext/libmemcached-0.32/libmemcached/memcached_fetch.c
index d3f0121..f088ff9 100644
--- a/ext/libmemcached-0.32/libmemcached/memcached_fetch.c
+++ b/ext/libmemcached-0.32/libmemcached/memcached_fetch.c
@@ -52,27 +52,54 @@ memcached_result_st *memcached_fetch_result(memcached_st *ptr,
   }

   if (result == NULL)
-    if ((result= memcached_result_create(ptr, NULL)) == NULL)
+    if ((result= memcached_result_create(ptr, NULL)) == NULL) {
+      *error= MEMCACHED_MEMORY_ALLOCATION_FAILURE;
       return NULL;
+    }

+  *error= MEMCACHED_MAXIMUM_RETURN; // We use this to see if we ever go into the loop
   while ((server = memcached_io_get_readable_server(ptr)) != NULL) 
   {
     char buffer[MEMCACHED_DEFAULT_COMMAND_SIZE];
     *error= memcached_response(server, buffer, sizeof(buffer), result);

-    if (*error == MEMCACHED_SUCCESS)
+    if (*error == MEMCACHED_SUCCESS) {
+      result->count++;
       return result;
-    else if (*error == MEMCACHED_END)
+    } else if (*error == MEMCACHED_END)
       memcached_server_response_reset(server);
     else
       break;
   }

+  if (*error == MEMCACHED_NOTFOUND && result->count)
+  {
+    *error= MEMCACHED_END;
+  }
+  else if (*error == MEMCACHED_MAXIMUM_RETURN && result->count)
+  {
+    *error= MEMCACHED_END;
+  }
+  else if (*error == MEMCACHED_MAXIMUM_RETURN) // while() loop was never entered
+  {
+    *error= MEMCACHED_NOTFOUND;
+  }
+  else if (*error == MEMCACHED_SUCCESS)
+  {
+    *error= MEMCACHED_END;
+  }
+  else if (result->count == 0)
+  {
+    *error= MEMCACHED_NOTFOUND;
+  }
+
   /* We have completed reading data */
   if (result->is_allocated)
     memcached_result_free(result);
-  else
+  else {
+    result->count = 0;
     memcached_string_reset(&result->value);
+  }

   return NULL;
 }
diff --git a/ext/libmemcached-0.32/libmemcached/memcached_result.c b/ext/libmemcached-0.32/libmemcached/memcached_result.c
index 0d77130..49545b7 100644
--- a/ext/libmemcached-0.32/libmemcached/memcached_result.c
+++ b/ext/libmemcached-0.32/libmemcached/memcached_result.c
@@ -22,6 +22,7 @@ memcached_result_st *memcached_result_create(memcached_st *memc,
   }

   ptr->root= memc;
+  ptr->count= 0;
   memcached_string_create(memc, &ptr->value, 0);
   WATCHPOINT_ASSERT(ptr->value.string == NULL);

@@ -31,6 +32,7 @@ memcached_result_st *memcached_result_create(memcached_st *memc,
 void memcached_result_reset(memcached_result_st *ptr)
 {
   ptr->key_length= 0;
+  ptr->count= 0;
   memcached_string_reset(&ptr->value);
   ptr->flags= 0;
   ptr->cas= 0;
diff --git a/ext/libmemcached-0.32/libmemcached/memcached_result.h b/ext/libmemcached-0.32/libmemcached/memcached_result.h
index e7ce012..e9b61eb 100644
--- a/ext/libmemcached-0.32/libmemcached/memcached_result.h
+++ b/ext/libmemcached-0.32/libmemcached/memcached_result.h
@@ -21,6 +21,7 @@ struct memcached_result_st {
   size_t key_length;
   uint64_t cas;
   memcached_string_st value;
+  uint64_t count;
   char key[MEMCACHED_MAX_KEY];
   /* Add result callback function */
 };

[evan]

These changes don't consistently pass tests for me. Can you put together a regular pull request with both and make sure the tests all pass?

[tmm1]

I'm seeing failures as well, stuff like:

<Memcached::ABadKeyWasProvidedOrCharactersOutOfRange> exception expected but was
Class: <Memcached::ATimeoutOccurred>
Message: <"Key {\"i have a space\"=>nil}">

I tried to dig in but can't figure out what's going on.

[evan]

Do you see them on master? Master is clean for me.

[tmm1]

Master is clean.

My patch is introducing a number of failures. I was able to fix some of them, but I can't figure out why bad keys are causing timeout errors with the patch.

At this point, I think time would be better spent upgrading the libmemcached dependency inside the gem. I took at stab at this, but ran into some issues with the CC settings in extconf since upstream is now C++.

[evan]

If you want to fork and do the upgrade, ok, but I can't upgrade this gem because libmemcached > 0.4 had a bunch of performance regressions that are unlikely to be fixed. See #80, #27.

[evan]

This guy seems to have a fork with an upgraded lib: https://github.com/chetan/memcached/tree/1.0.14

I tried to run it but got segfaults. Maybe you can get it working and do a benchmark comparison.