ourdelta-developers team mailing list archive

[MARK CALLAGHAN <mdcallag@xxxxxxxxx>]

On Thu, Mar 5, 2009 at 1:06 PM, Arjen Lentz <arjen@xxxxxxxxxxxxxxxx> wrote:
> Hi Mark,
>
> On 06/03/2009, at 1:15 AM, MARK CALLAGHAN wrote:
>> Well, I fixed this and then I removed all code for SHOW
>> CLIENT_STATISTICS from the next patch. We were not using it enough
>> to justify the cost of having that code there. SHOW INDEX_STATISTICS
>> has been removed as well. SHOW TABLE_STATS and SHOW USER_STATS
>> remain with changes to fix the mutex contention that they used to
>> create. I don't know what Percona will do with that. They may be
>> bigger fans of SHOW INDEX_STATS than I was.
>
>
> INDEX_STATISTICS allows us to find unused indexes, and that's very
> valuable.
> Don't care for the SHOW commands as such, in INFORMATION_SCHEMA
> they're much more useful as they can be joined onto other tables to do
> the unused-index detection.
>
> Don't think OurDelta will be removing that, it's specifically why we
> included it.
>

Then you have inherited a mutex contention performance bug. I fixed it
by removing the feature. There are other ways to fix it that require
more code changes. But it needs to be fixed.

>
> Cheers,
> Arjen.
> --
> Arjen Lentz, Director @ Open Query (http://openquery.com)
> Affordable Training and Pro-Active Support for MySQL & related
> technologies
>
> My blog is at http://arjen-lentz.livejournal.com
> OurDelta: free enhanced builds for MySQL @ http://ourdelta.org
>
> --
> CLIENT_STATISTICS are broken if hostname is > 16 chars
> https://bugs.launchpad.net/bugs/338012
> You received this bug notification because you are a member of OurDelta-
> developers, which is the registrant for OurDelta.
>
> Status in OurDelta - Builds for MySQL: New
>
> Bug description:
>
> I noticed today that the CLIENT_STATISTICS tables were not working properly if the hostnames are longer
> than 16 characters.  I am running these packages from the ourdelta repository (centos5.2):
>
> MySQL-OurDelta-client.x86_64             5.0.67.d7-44.el5_2     installed
> MySQL-OurDelta-server.x86_64             5.0.67.d7-44.el5_2     installed
> MySQL-OurDelta-shared.x86_64             5.0.67.d7-44.el5_2     installed
>
> mysql> select count(*) from client_statistics;
> +----------+
> | count(*) |
> +----------+
> |  1485697 |
> +----------+
> 1 row in set (1.62 sec)
>
> mysql> select client from client_statistics limit 20;
> +------------------+
> | client           |
> +------------------+
> | gonzo17i.bunchba |
> |                  |
> | gonzo23i.bunchba |
> | gonzo20i.bunchba |
> | gonzo20i.bunchba |
> | gonzo23i.bunchba |
> | gonzo20i.bunchba |
> | gonzo20i.bunchba |
> | gonzo17i.bunchba |
> | gonzo17i.bunchba |
> | gonzo20i.bunchba |
> | gonzo23i.bunchba |
> | gonzo20i.bunchba |
> | gonzo17i.bunchba |
> | gonzo23i.bunchba |
> | gonzo20i.bunchba |
> | gonzo17i.bunchba |
> | gonzo20i.bunchba |
> | gonzo15i.bunchba |
> | gonzo17i.bunchba |
> +------------------+
> 20 rows in set (1.36 sec)
>
>
> As you can see, there are lots of duplicate rows.  The heart of the problem seems to be this
> code from the google patch:
>
> ourdelta-mybranch/mysql/5.0/google/userstatsv2/userstatsv2-main.patch.
>
> Client name lengths are set to LIST_PROCESS_HOST_LEN (64), but the CLIENT column is set to 16 characters.
> This means that there will be rows in client stats table that will be distinct, but indistinguishable in the show client_statistics output.  The CLIENT column should probably have the same length (its set in this line:
>
> +  {"CLIENT", 16, MYSQL_TYPE_STRING, 0, 0, "Client"},
>
> But the underlying problem seems to be in a different place.
>
> There is a routine to initialize the statistics:
>
> +void init_global_client_stats(void)
> +{
> +  if (hash_init(&global_client_stats, system_charset_info, max_connections,
> +                0, 0, (hash_get_key)get_key_user_stats,
> +                (hash_free_key)free_user_stats, 0)) {
> +    sql_print_error("Initializing global_client_stats failed.");
> +    exit(1);
> +  }
> +}
>
> The get_key_user_stats is shared between the global_user_stats and global_client_stats hash tables.
> Here is the definition of that function:
>
> +byte *get_key_user_stats(USER_STATS *user_stats, uint *length,
> +                         my_bool not_used __attribute__((unused)))
> +{
> +  *length = strlen(user_stats->user);
> +  return (byte*)user_stats->user;
> +}
>
> The "user_name" field is being shared between user and client statistics.  This field is limited to 16 characters.  But when a hash match is being looked for, we are comparing against a 64 char host name, and we are always inserting a new row.
>
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-- 
Mark Callaghan
mdcallag@xxxxxxxxx