[Labs-l] Empty Cat query

[Huji Lee]

See https://quarry.wmflabs.org/query/12718 and the error message returned.

EXPLAIN only works if you have access to the underlying tables. I only have
access to the VIEWs built on top of actual wiki tables (for good reason,
same applies to most of us) so I get an error when I try EXPLAIN.

On Fri, Sep 23, 2016 at 11:24 AM, Jaime Crespo <jcrespo at wikimedia.org>
wrote:

> Explain (you should be able to run SHOW EXPLAIN on your own queries:
> http://s.petrunia.net/blog/?p=89):
>
> EXPLAIN select page_title, count(ll_lang) from page join category on
> page_title = cat_title left join categorylinks on page_title = cl_to left
> join templatelinks on tl_from = page_id and tl_namespace = 10 and tl_title
> in (   'رده_خالی' , 'رده_بهتر', 'رده_ابهام‌زدایی', 'رده_ردیابی‌کردن' ) left
> join langlinks on page_id = ll_from where page_namespace = 14 and
> page_is_redirect = 0 and cl_to is null and tl_title is null group by
> page_title order by 2, 1 limit 5000\G
> *************************** 1. row ***************************
>            id: 1
>   select_type: SIMPLE
>         table: page
>          type: ref
> possible_keys: name_title,page_redirect_namespace_len
>           key: page_redirect_namespace_len
>       key_len: 5
>           ref: const,const
>          rows: 364273
>         Extra: Using where; Using temporary; Using filesort
> *************************** 2. row ***************************
>            id: 1
>   select_type: SIMPLE
>         table: category
>          type: eq_ref
> possible_keys: cat_title
>           key: cat_title
>       key_len: 257
>           ref: fawiki.page.page_title
>          rows: 1
>         Extra: Using index
> *************************** 3. row ***************************
>            id: 1
>   select_type: SIMPLE
>         table: categorylinks
>          type: ref
> possible_keys: cl_timestamp,cl_sortkey
>           key: cl_timestamp
>       key_len: 257
>           ref: fawiki.page.page_title
>          rows: 12
>         Extra: Using where; Using index
> *************************** 4. row ***************************
>            id: 1
>   select_type: SIMPLE
>         table: templatelinks
>          type: ref
> possible_keys: tl_from,tl_namespace
>           key: tl_namespace
>       key_len: 4
>           ref: const
>          rows: 390610
>         Extra: Using where; Using index
> *************************** 5. row ***************************
>            id: 1
>   select_type: SIMPLE
>         table: langlinks
>          type: ref
> possible_keys: ll_from
>           key: ll_from
>       key_len: 4
>           ref: fawiki.page.page_id
>          rows: 104910
>         Extra: Using index
>
> On Fri, Sep 23, 2016 at 5:16 PM, Huji Lee <huji.huji at gmail.com> wrote:
>
>> Hi all,
>>
>> I have a query [1] which I run weekly to identify empty categories; those
>> that don't have interwiki links and stay empty for a while are then deleted
>> by a sysop.
>>
>> The query ran just fine every week until Sep 2nd. [2] Since then, the
>> query times out and the page doesn't get updated.
>>
>> The query is no that complex (a SELECT with five JOINs) and used to
>> finish in about 3-5 minutes. I don't have EXPLAIN access on Labs so I
>> cannot tell what is slowing it down. Can someone kindly take a look and
>> advise why this suddenly stopped working?
>>
>> Thanks,
>>
>> Huji
>>
>> [1] https://quarry.wmflabs.org/query/3760
>> [2] https://fa.wikipedia.org/w/index.php?title=%D9%88%DB%8C%DA%
>> A9%DB%8C%E2%80%8C%D9%BE%D8%AF%DB%8C%D8%A7:%DA%AF%D8%B2%D8%
>> A7%D8%B1%D8%B4_%D8%AF%DB%8C%D8%AA%D8%A7%D8%A8%DB%8C%D8%B3/
>> %D8%B1%D8%AF%D9%87%E2%80%8C%D9%87%D8%A7%DB%8C_%D8%AE%D8%
>> A7%D9%84%DB%8C&action=history&uselang=en
>>
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>>
>>
>
>
> --
> Jaime Crespo
> <http://wikimedia.org>
>
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