MySQL Bugs: #22821: Adding "SHOW HOST_CACHE" patch from Jeremy Cole

Bug #22821	Adding "SHOW HOST_CACHE" patch from Jeremy Cole
Submitted:	29 Sep 2006 13:51	Modified:	20 Aug 16:18
Reporter:	Jacques
Status:	Verified
Category:	Server	Severity:	S4 (Feature request)
Version:	5.0-community	OS:	Any
Assigned to:	Sergey Gluhov	Target Version:
Tags:	Contribution
Triage:	Needs Triage: D5 (Feature request) / R2 (Low) / E3 (Medium)

Description:
Please seriously consider adding the http://jcole.us/patches/mysql/5.0/host_cache/ patch
from Jeremy Cole to MySQL 5.0 and 5.1.  More information about what these patches do is
available over at
http://jcole.us/blog/archives/2006/09/26/followup-on-ips-hostnames-and-mysql/

There is currently no way of figuring out which hosts are in the host cache or tuning the
number of hosts that can be cached via SET GLOBAL variables.

How to repeat:
Apply the patches :)

Suggested fix:
Add the patches over @ http://jcole.us/patches/mysql/5.0/host_cache/ namely:

 * http://jcole.us/patches/mysql/5.0/host_cache/00_hash_filo.patch
 * http://jcole.us/patches/mysql/5.0/host_cache/01_my_gethostbyaddr_r.patch
 * http://jcole.us/patches/mysql/5.0/host_cache/02_hostname_cache.patch
 * http://jcole.us/patches/mysql/5.0/host_cache/03_host_cache_size.patch
 * http://jcole.us/patches/mysql/5.0/host_cache/04_show_host_cache.patch
 * http://jcole.us/patches/mysql/5.0/host_cache/05_host_cache_metrics.patch

Thank you for a reasonable feature request.

This bug has duplicate Bug #17171.

I refused the new SHOW command, and instead added a new table to the information schema.

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/17680

ChangeSet@1.2359, 2007-01-05 13:31:05-05:00, cmiller@zippy.cornsilk.net +17 -0
  Bug#22821: Adding "SHOW HOST_CACHE" patch from Jeremy Cole
  
  This doesn't implement "SHOW HOST_CACHE" as a command, but it
  does add the same functionality as a table in the system infor-
  mation schema.

A couple of comments for this patch:

- FLUSH GLOBAL STATUS should reset the hostname cache statistics.
  To do this there is two possible solutions:
  - Move the metrics into STATUS_VAR
  - Add the hostname metrics structure into STATUS_VAR. In this case one must   however
ensure that all variables are of type 'ulong'.

- Ensure that we follow the same coding standard in the new code as in the old.
  Some examples:
  - Space after 'if'
  - Only one statement per row (ie, break 'if () statement' into two lines

Can we add an additional feature to this patch? The feature would allow us to FLUSH HOSTS
just for a particular hostname. For example:

mysql> FLUSH HOSTS LIKE "%.example.org";

shell>  mysqladmin hosts-flush "%.example.org" (not sure what syntax to use here, perhaps
regexps)

Suggest to use the patch but make an information schema table instead.