Re: High ID (unique, auto increment) causes slow responses on PHP (MySQL)

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On Sat, Jun 13, 2009 at 3:34 PM, Stuart<stuttle@xxxxxxxxx> wrote:
> 2009/6/13 דניאל דנון <danondaniel@xxxxxxxxx>:
>>  I've built a certain system where every time new user enters it creates a
>> "guest row" on "guests" table. he also gets an identifying cookie.
>>
>> The table contains several fields, one of them is ID which is auto increment
>> and unique
>>
>> When he does a certain action it gets recorded in the "done_action" table
>> with several fields on it, one of them is "guest_id" and his ID on it.
>>
>>
>> Problem is the guests table has about 30,000 rows (which means ID is high).
>>
>>  I was wondering whether I should somehow change how the system works.
>>
>> I've thought about couple of options
>>
>> A weekly "cleanup" job. opens a table called "guests_tmp", *copies* all data
>> from guests to guests_tmp.
>>
>> every row it copies it also changes the ID on the table done_action.
>>
>> What do you  think?
>
> I think your problem has nothing to do with high IDs. I have tables in
> MySQL with primary key IDs that have recently passed 2 billion and
> they're still as responsive as they were with 1 row!!
>
> What specific operations are slow, and are you sure it's the MySQL
> query that's being slow and not something in the surrounding code? If
> it is the MySQL query what is it and what engine are your tables
> using?
>
> -Stuart
>
> --
> http://stut.net/
>

Right. 30k rows in most databases is nothing. Neither the number of
rows nor the size of the number should cause problems at that size. Is
there a chance that the table is incorrectly indexed? Every index has
to be updated when a new row is added, so a table with a lot of
unnecessary indexes (for example, every column has its own index) can
get dreadfully slow as it fills up.

Andrew

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