Beware to say "Treat warning as an error" in new GCC

Are you building your something using Gcc(>=4.6) ?
If yes, then you used be more careful to use "treat warning as an error".
Recently I tried to build zbase over Ubuntu 12.04 2 which uses Gcc (4.6.2) and I faced lots of problem.
And then I moved to Gcc(4.2), everything was too smooth. No error or warnings.

Then I looked into Gcc release details and came across with few important points:

• -Wunused-but-set-variable and -Wunused-but-set-parameter warnings were added. Also the -Wunused-but-set-variable warning is enabled by default by -Wall flag and -Wunused-but-set-parameter by -Wall -Wextra flags.
• Also you may face few linkers problem. I faced a one with jemalloc.

For more about changes have a look here :)

In drizzle , I have to include "config.h" in each file to get rid of this type of error.

Setting Up a Drizzle Development Ubuntu Box

Sometimes we just get bored to figure out dependencies for drizzle development.

Ubuntu have a drizzle-dev package for development purpose. But for me it's not sufficient.

I follow this particular steps for box setup:

• Get Ubuntu 12.04 or whatever you like, install it on virtual box.
• Now after setting up Ubuntu VM-Box. Open terminal and type:
  
  sudo apt-get install bzr drizzle-dev autopoint libboost1.48-all-dev libprotobuf-dev protobuf-compiler uuid-dev libcloog-ppl
• Also you can try apt-get build-dep drizzle
• Now compile source as mention here.

What's new in Json Server ??

As a part of Drizzle , I just started changing the internals of JSON Server with the help of Stewart.
So, what's new ? . That is a big question for this plugin. Last time I did some re-factoring and implemented some new functionalities. Right now I am not focusing on functionality part too much. But yeah, plugin will come up with some new functionalities soon.

Previous version is capable of basic functionality like Insertion, deletion , selection etc. For more details look here. In previous versions , we generate a sql query by parsing json request and then execute that query with the help of Execute API. But Execute API restricts some functionality.

So I just tried to perform sql execution without Execute API. Now we just parse json query and uses parameter with Storage Engine API.

Right now we have two functionalities with such implementation:

• Create Schema
• Drop Schema

If you like to play with this, try out this branch (lp:~mohyt/drizzle/drizzle-json_server) .

How to play with it? , its too simple :

• Start your drizzle server with json plugin enabled (./drizzled/drizzled --plugin-add=json_server)
• Now send a curl request to create schema. For example,

 --exec curl -H "Content-Type: application/json" -H "Accept: application/json" -X POST -d '{"query":{"name":"json"}}' 'http://localhost:8086/json/ddl/schema/create'

• And , to drop a schema , try this ,  

--exec curl -H "Content-Type: application/json" -H "Accept: application/json" -X POST -d '{"query":{"name":"json"}}' 'http://localhost:8086/json/ddl/schema/drop'

Comments are most welcome :)

Design of AlsoSQL: Drizzle JSON HTTP Server

This particular project was proposed by Henrik at Drizzle Day 2011. A week later, Stewart published version 0.1 of AlsoSQL. Later I and Henrik worked on version 0.2 and he talked about it at Drizzle Day 2012 .

AlsoSQL:Drizzle JSON HTTP Server, is capable of SQL-over-HTTP with key-value operation in pure json. Henrik explained about its working and functionality in this particular post. 

Here,I am going to talk about design of AlsoSQL and the various problems I faced.

Up-to version 0.2 , the API wasn't properly object oriented, so we planned to do re-factoring first.

After going through the code-base of AlsoSQL, I realized the need of design pattern. So we looked through various of them and chose Fascade design pattern for future development.

Here is the rough design of AlsoSQL (I called it rough because it might change in future).

Description:

HttpHandler is used to handle the http request ,parsing and validating json from that request and sending back response.

SQLGenerator simply generates the sql string corresponding to request type using input json.

SQLExecutor executes the sql and returns resultset.

SQLToJsonGenerator generates the output json corresponding to request type.

DBAccess is an interface to access generators and executor.

The main reason to design it in such a way is that it can be used over storage engine in future directly.

Problems Faced:

<config.h> , I always forgot to include this header file and it floods error on my terminal.

Another one , I need to get LAST_INSERT_ID() and I want to get it in a single query with REPLACE query. Still working on it.

Debug Drizzle Code with GDB

From last few days , I have been working on a bug in JSON Server of Drizzle. And the bug is of Segmentation fault , which is not easy to recognize by just reading the code-base. So , the best way to get rid of this problem is  to debug the code. But How ?
I used Visual Studio once during my internships to debug a project. So ,I tried to find out some IDEs that can be use with drizzle . But I figured it out as we can debug a C++ code-base easily and efficiently with GDB .

Here are few steps for debugging:

First of all build your server and enable debugging:

mohit@mohit-PC:~$ cd repos/drizzle/drizzle-json_server/

mohit@mohit-PC:~/repos/drizzle/drizzle-json_server$ ./config/autorun.sh && ./configure --with-debug && make install -j2

Default installation path is /usr/local/ but you can change it with --prefix = /installation_path/
Start server and debug the code:

mohit@mohit-PC:~/repos/drizzle/drizzle-json_server$ gdb /usr/local/sbin/drizzled >

Now set arguments needed to start server with specific plugin (In my case , plugin is json_server)

(gdb) set args --plugin-add=json_server

Set breakpoints,you can do that with this command:
 b <filename>:<line-number> or break <filename>:<line-number>

(gdb) break json_server.cc:1093

Since the json_server plugin is not loaded yet , hence it prompts with :

No source file named json_server.cc.
Make breakpoint pending on future shared library load? (y or [n])

Go with "y"
Run your server now :

(gdb) r

You will get something like this:

Starting program: /usr/local/sbin/drizzled --plugin-add=json_server
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".

Now you can use various commands of GDB to debug your code.
List of these commands are mentioned here.

Problem Faced :

Once I started drizzle server with plugin. I got a message:

Using host libthread_db library "/lib/i386-linux-gnu/libthread_db.so.1".
/usr/local/sbin/drizzled: relocation error: /usr/local/sbin/drizzled: symbol _ZN8drizzled7message6AccessC1Ev, version DRIZZLE7 not defined in file libdrizzledmessage.so.0 with link time reference
[Inferior 1 (process 23532) exited with code 0177]

I was unable to get a single line of this problem, Thank to Henrik for solution.

Solution:

mohit@mohit-PC:~$ sudo rm /etc/ld.so.cache
mohit@mohit-PC:~$ ldconfig

Toru and Padraig previously posted on this topic which may also be helpful.
Also You can find documentation on this at Drizzle wiki.

Calculating Value During Compile Time In C++

"If you think it's simple, then you have misunderstood the problem" - Bjarne Stroustrup

Recently one of my colleague asked me a question:

Print the value of (1 + 100 * 10 - 5 / 2 + 30) expression during compile time. And he allowed me to use any programming language.

For a while , I was not able to get the answer of this question. But after spending few minutes , I found out it's a good conceptual question.
The answer of this problem is simple, if you know about Templates in C++ a bit.

What are Templates?
Templates are a feature of the C++ programming language that allow functions and classes to operate with generic types. This allows a function or class to work on many different data types without being rewritten for each one.


The solution is based on Template Meta-Programming.
Template meta-programming is a technique in which templates are used by a compiler to generate temporary source code, which is merged by the compiler with the rest of the source code and then compiled. More on wiki.

#include <iostream>

using namespace std;
template<unsigned int n>
struct Expression {
   static const float result = n;
};

template<unsigned int exp>
struct _{ operator char() { return exp;} };

int main() {
        char(_<Expression<1 + 100 * 10 - 5 / 2 + 30>::result>());
        return 0;
}

If you want to explore more , try to print Factorial<n> ;)

"Undefined Reference" While Using Templates In C++

Did you get "collect2: ld returned 1 exit status" ??

If yes , then there is some linker's problem. Lets solve it.

I designed a template for one of my assignment , But I was unaware of "Declaring & Defining" fundamentals of templates in C++.

Here is some code :

//Add.h

#include "Basic.h"
using namespace std;
template <class T>
class Add{

        int x;
        int y;
        
public:
      Add(int x,int y);
      Dump();
};

Add.cpp

#include "Add.h"

template <class T>
Add<T>::Add(int x,int y):x(1),y(2){};


template <class T>
Add<T>::Dump(){
 cout<<x<<"  "<<y;
}

Output:
collect2: ld returned 1 exit status

Reason:
Templates are just a recipe , they are not code. In order to compile this code, it must be generated first, which needs to know templates definition & definition parameters which are passed to it. And compiler does not know about separate compilation (compiler doesn't know about anything about code outside of a file).

Solution:
Put the definitions in the header files itself :)

//Add.h

#include "Basic.h"
using namespace std;
template <class T>
class Add{

        int x;
        int y;
        
public:
      Add(int x,int y);
      Dump();
};

template <class T>
Add<T>::Add(int x,int y):x(1),y(2){};

template <class T>
Add<T>::Dump(){
 cout<<x<<"  "<<y;
}