Because of I want to test some funtions of the SQLite.
According to Clemens said, the testing result may be influenced by cache.
How could avoid the influence of cache? Is there funtion can eliminate the
influence?
best regards.
WQG
At 2015-12-11 15:40:56, "Clemens Ladisch" <clemens at ladisch.de> wrote:
>??? wrote:
>> For example, tableA contains two columns: implicit rowid, A_id.
>> we create index on A_id.
>> firstly, we used rowid to select the row, cost about 400 seconds;
>> secondly, we used A_id to select the row, cost about 200 seconds;
>> thirdly, we also used rowid to select the row, cost about 200 seconds.
>
>This can be explained by the data being cached.
>
>> if firstly,we used A_id to select the row, cost about 200 seconds;
>> the create index on A_id may have some influence to do with the rowid.
>> and from this example, I also think the rowid is not implicit index.
>
>If all columns of the table are contained in the index, then the "select *"
>can read all values from the index itself, without having to look up the
>row in the original table. This is called a covering index.
>
>If your table has more columns, lookups on A_id will become slower.
>
>
>Regards,
>Clemens
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