Thanks for your reply. I would like to know how the register allocation decision is made and the part of the code which does it . can you please help me find that? Thanks On 18 Sep 2014 20:20, "Richard Hipp" <d...@sqlite.org> wrote:
> On Thu, Sep 18, 2014 at 10:10 AM, Prakash Premkumar < > prakash.p...@gmail.com> > wrote: > > > Which function in the sqlite generates the Vdbe program for the given > > query? > > > > Let's take an example of the join of two tables. Table A has n columns > and > > Table B has m columns, and the result has n+m columns. > > > > During the execution of the Vdbe program the values from these columns > get > > copied to the Mem struct randomly (when OP_Column opcode is formed) and > > finally when the OP_ResultRow is executed, the Mem's are rearranged so > that > > the columns of each table are contiguous. > > > > How does sqlite know in which Mem the value of a column is stored and how > > does it finally rearrange the Mems contiguously? > > Can you point me to the portion of the source code which makes this > > decision? > > > > Can you kindly explain me the concept? > > > > SQLite is a compiler. It transforms a high-level language (SQL) into > machine code (or in this case VDBE code, which is very similar to machine > code). In this sense, SQLite is similar to GCC. GCC translates C code > into x86 assembly language. SQLite translates SQL into VDBE assembly > language. The source and target languages are different, but the > fundamental techniques are the same. > > When you ask "how does sqlite know which Mem the value of a column is > stored?" that is the same as asking "how does gcc know which processor > registers the value of a variable is stored?". > > I recommend that you first study up on compiler construction. After you > understand how compilers work, SQLite will likely make a lot more sense to > you. > > -- > D. Richard Hipp > d...@sqlite.org > _______________________________________________ > sqlite-users mailing list > sqlite-users@sqlite.org > http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users > _______________________________________________ sqlite-users mailing list sqlite-users@sqlite.org http://sqlite.org:8080/cgi-bin/mailman/listinfo/sqlite-users
