Re: [Cppcms-users] Avoid loading query results completely into cppdb::result

[Alexander M. <a....@ev...>]

Hello Artyom,

You are right. The problem has been the buffer-size in MySQL.
Thank you very much for the fast answer!

Alex



Am 01.04.2015 um 12:19 schrieb Artyom Beilis:
> CppDB (if the backed allows) fetches the data row by row and not the 
> entire collection:
>
> Unprepared statements: 
> http://sourceforge.net/p/cppcms/code/HEAD/tree/cppdb/trunk/drivers/mysql_backend.cpp#l75
> Prepared statement: 
> http://sourceforge.net/p/cppcms/code/HEAD/tree/cppdb/trunk/drivers/mysql_backend.cpp#l510
> cppdb::result is sort of cursor you iterate over the data set.
>
> The delay probably caused by initial query and not fetching itself.
>
> Artyom Beilis
> --------------
> CppCMS - C++ Web Framework:   http://cppcms.com/
> CppDB - C++ SQL Connectivity: http://cppcms.com/sql/cppdb/
>
>     ------------------------------------------------------------------------
>     *From:* Alexander Mack (EvalSys) <a....@ev...>
>     *To:* cpp...@li...
>     *Sent:* Wednesday, April 1, 2015 12:36 PM
>     *Subject:* [Cppcms-users] Avoid loading query results completely
>     into cppdb::result
>
>     Dear Artyom, Dear community,
>
>     I was wondering if it's possible, to avoid loading the complete
>     query result into cppdb::result but handle the query results "step
>     by step"?
>
>     If I'm running the following query on a bigger database
>
>     <code>
>
>     cppdb::result  <http://cppcms.com/sql/cppdb/classcppdb_1_1result.html>  r = sql <<"SELECT name,age FROM students";
>
>     </code>
>
>     it takes a lot of time to copy all the results into the
>     cppdb::result container. For testing I tried that for about 6 mio
>     entries..
>
>     I didn't work with the original MySQL-lib yet.. but if I send the
>     query using the standard MySQL lib e.g.
>
>     <code>
>
>     |
>        res=  mysql_perform_query(conn,  "SELECT * FROM students");
>
>        while  ((row=  mysql_fetch_row(res))  !=NULL)
>            ....|
>
>     </code>
>
>     it seems that the interface delivers single rows only, if I'm
>     fetching the result (row by row).
>
>     Now I was wondering, if there is some technique / flag to do the
>     same with cppdb?
>
>     In the end I'm trying to run through a big amount of data. If I'm
>     trying offset/limit combinations, it gets very slow as soon as
>     offset increases..
>
>     It'd be great, if someone would have a tipp for me.
>
>     Thank you very much,
>
>     Alex
>
>
>
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