Re: [sqlite] Amount of memory for caching one page with x byte page size?

2008-07-20 Thread Dan

On Jul 21, 2008, at 2:10 AM, [EMAIL PROTECTED] wrote:

>
> Hello,
>
> to answer the following question:
>
> Amount of memory for caching one page with x byte page size?
>
> I found in the Draft 3.6.0 Doc the following information:
>
>
> PRAGMA page_size = bytes;
>
> Query or set the page size of the database.
> The page size may only be set if the database has not yet been  
> created.
> The page size must be a power of two greater than or equal to 512 and
> less than or equal to SQLITE_MAX_PAGE_SIZE.
> The maximum value for SQLITE_MAX_PAGE_SIZE is 32768.
>
>
>
> PRAGMA default_cache_size = Number-of-pages;
>
> Query or change the maximum number of database disk pages that SQLite
> will hold in memory at once.
> Each page uses 1K on disk and about 1.5K in memory. ...
>
>
> Obviously you have an overhand per page-size to calculate the memory
> requirement for caching on page.
>
> Do I understand this right?

Right. When a page is loaded into the cache, SQLite allocates memory
for the page data (1024 bytes, or whatever size you are using) and also
memory for a structure full of other variables required by each cached
page (page number, dirty flag, is-journalled flag, various pointers
for linked lists, lots of stuff). The overhead probably isn't quite
512 bytes, but as a rule of thumb this formula works Ok.

Dan.

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[sqlite] Amount of memory for caching one page with x byte page size?

2008-07-20 Thread [EMAIL PROTECTED]

Hello,

to answer the following question: 

Amount of memory for caching one page with x byte page size? 

I found in the Draft 3.6.0 Doc the following information:


PRAGMA page_size = bytes;

Query or set the page size of the database.
The page size may only be set if the database has not yet been created.
The page size must be a power of two greater than or equal to 512 and 
less than or equal to SQLITE_MAX_PAGE_SIZE.
The maximum value for SQLITE_MAX_PAGE_SIZE is 32768. 



PRAGMA default_cache_size = Number-of-pages;

Query or change the maximum number of database disk pages that SQLite
will hold in memory at once.
Each page uses 1K on disk and about 1.5K in memory. ...


Obviously you have an overhand per page-size to calculate the memory
requirement for caching on page.

Do I understand this right?

kind regards

Rainer






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