Hello,
A MySQL developer would be able to answer to these questions more
accurately, but I'll try to answer _logically_. So don't bet a million
dollars on the correctness of my answer.
> >>NOTE: The query cache does not return stale data. When data is modified,
> any relevant entries in the query cache are flushed. <<
>
> If I have a select statement like:
>
> select col1, col2 from table1 where col1='A'
>
> 1) will the cache be flushed if someone changes a non-referenced column for
> one of the retrieved rows:
>
> Update table1 set col3 = 'x' where col1='A'
>
> this update changes col3 that falls within the Where of the query but it
> affects a column that is not returned by the query.
I think this flushes the cache. Think about a situation where col1 is a
computed column that derives its values from the data in col3. When col3
is updated, the value of col1 in the query cache would become invalid.
> 2) or will the cache be flushed if someone changes a row that falls outside
> of the query's Where clause:
This shouldn't explicitly flush the cache, but I don't know the details of
the implementation. This insert shouldn't have any effect on the
aforementioned SELECT query, because col1 here is 'D'.
> insert into table1 (col1, col2, col3) values('D', 'x', 'y');
>
> This last query updates the same table as the select query, but the row
> that is added is outside the range of the query's where clause.
>
>
> So how smart is the cache?
> a) Is it smart enough to allow table updates and if the update doesn't
> affect the query, will it continue to use the cache? (This requires a lot
> of intelligence.)
> b) Or will any update to the rows that fall within the range of the query
> (regardless of whether the column is in the query) will flush the cache?
> c) Or will any update to the table automatically flush the cache?
>
> MONTY:
> I would like to see the Explain command to say if it is using the cache or
> not (CACHE:Yes/No). This would help developers make better use of the cache
> if they know how what affects it.
>
> Mike
>
>
******************************************
* Iikka Meriläinen *
* E-mail: [EMAIL PROTECTED] *
* Vaala, Finland *
******************************************
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