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Date: Fri, 27 Sep 2024 22:42:10 -0400
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Subject: Re: Apache + mod_php performance
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On 9/27/2024 10:19 PM, Lawrence D'Oliveiro wrote:
> On Fri, 27 Sep 2024 22:13:09 -0400, Arne Vajhøj wrote:
>> On 9/27/2024 10:01 PM, Lawrence D'Oliveiro wrote:
>>> On Fri, 27 Sep 2024 21:58:57 -0400, Arne Vajhøj wrote:
>>>> If volume requires sharding then ...
>>>
>>> “Sharding” means “split across multiple physical persistent storage”.
>>
>> It means that you have N active database servers each with 1/N of the
>> data (possible with replication to N or 2N passive database servers).
> 
> Quite unnecessary, given that the bottleneck is the usually the latency
> and bandwidth of the persistent storage, not the CPU.

I don't think Facebook could move their 1800 MySQL shards onto
a single server.

> Particularly since your network connections introduce latency and
> bandwidth limitations of their own.

That is not the problem with shards. Applications are usually OK
with network latency.

The problem with shards is that not all data usage models fit
nicely with sharding.

If you need to get/update a row by primary key then sharding
works perfect - you go to the right server and just do it.

If you need to get/update a number of rows and you don't
know which servers they are on, then it means querying all
servers, which both create performance and consistency
problems.

Arne