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Posted to user@ignite.apache.org by John Wilson <sa...@gmail.com> on 2017/09/07 21:22:36 UTC

Why is PageSize limited to just 16kB?

Hi,

Ignite sets the maximum possible size for a page to 16KB. Why? What are the
drawbacks of having bigger page sizes?

https://github.com/apache/ignite/blob/bd7bd226d959fbc686f6104a048106b7b944347b/modules/core/src/main/java/org/apache/ignite/configuration/MemoryConfiguration.java#L179


Thanks,

Re: Why is PageSize limited to just 16kB?

Posted by John Wilson <sa...@gmail.com>.

Thanks Dmitry!

On Fri, Sep 8, 2017 at 4:57 AM, Dmitry Pavlov <dp...@gmail.com> wrote:

> Hi John,
>
>
>
> Quite long page will require Ignite to use much time during loading page
> from disk or write it back during checkpointing. Ignite is able to change
> field value pointwise within page in case of update. In that case and if
> too long page is selected, one field update, for example 1 byte will
> require ignite to checkpoint 16K+ of data at next checkpoint.
>
>
>
> Going deeply to techical details: 16 K limitation came from internal
> 2-byte addressing of data within page. There is internal offset named
> 'item' which is 2 bytes in length and has 2 bits flags in it. 2^14=16384
>
>
>
> Sincerely,
>
> Dmitriy Pavlov
>
>
> пт, 8 сент. 2017 г. в 0:22, John Wilson <sa...@gmail.com>:
>
>> Hi,
>>
>> Ignite sets the maximum possible size for a page to 16KB. Why? What are
>> the drawbacks of having bigger page sizes?
>>
>> https://github.com/apache/ignite/blob/bd7bd226d959fbc686f6104a048106
>> b7b944347b/modules/core/src/main/java/org/apache/ignite/configuration/
>> MemoryConfiguration.java#L179
>>
>> Thanks,
>>
>

Re: Why is PageSize limited to just 16kB?

Posted by Dmitry Pavlov <dp...@gmail.com>.

Hi John,



Quite long page will require Ignite to use much time during loading page
from disk or write it back during checkpointing. Ignite is able to change
field value pointwise within page in case of update. In that case and if
too long page is selected, one field update, for example 1 byte will
require ignite to checkpoint 16K+ of data at next checkpoint.



Going deeply to techical details: 16 K limitation came from internal 2-byte
addressing of data within page. There is internal offset named 'item' which
is 2 bytes in length and has 2 bits flags in it. 2^14=16384



Sincerely,

Dmitriy Pavlov


пт, 8 сент. 2017 г. в 0:22, John Wilson <sa...@gmail.com>:

> Hi,
>
> Ignite sets the maximum possible size for a page to 16KB. Why? What are
> the drawbacks of having bigger page sizes?
>
>
> https://github.com/apache/ignite/blob/bd7bd226d959fbc686f6104a048106b7b944347b/modules/core/src/main/java/org/apache/ignite/configuration/MemoryConfiguration.java#L179
>
>
> Thanks,
>