DEV Community: yuyabu

gnu time(usr/bin/time) can check process memory usage,without vmstat or sar

yuyabu — Mon, 08 Apr 2019 05:46:30 +0000

There are two types of time commands.

bash built-in time command
gnu time

The gnu time command can measure cpu usage, average memory usage, maximum memory usage, etc.
Although the default output format is hard to see, users can define their own format and select only the necessary information.

Environmental information

$ cat /etc/lsb-release
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=18.04
DISTRIB_CODENAME=bionic
DISTRIB_DESCRIPTION="Ubuntu 18.04.2 LTS"

FORMATTING THE OUTPUT  

| %  | A literal `%'.                                                                                                                                                                                                                                 | 
|----|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| 
| C  | Name and command line arguments of the command being timed.                                                                                                                                                                                    | 
| D  | Average size of the process's unshared data area, in Kilobytes.                                                                                                                                                                                | 
| E  | Elapsed real (wall clock) time used by the process, in [hours:]minutes:seconds.                                                                                                                                                                | 
| F  | Number of major, or I/O-requiring, page faults that occurred while the process was running.  These are faults where the page has actually migrated out of primary memory.                                                                      | 
| I  | Number of file system inputs by the process.                                                                                                                                                                                                   | 
| K  | Average total (data+stack+text) memory use of the process, in Kilobytes.                                                                                                                                                                       | 
| M  | Maximum resident set size of the process during its lifetime, in Kilobytes.                                                                                                                                                                    | 
| O  | Number of file system outputs by the process.                                                                                                                                                                                                  | 
| P  | Percentage of the CPU that this job got.  This is just user + system times divided by the total running time.  It also prints a percentage sign.                                                                                               | 
| R  | Number of minor, or recoverable, page faults.  These are pages that are not valid (so they fault) but which have not yet been claimed by other virtual pages.  Thus the data in the page is still valid but the system tables must be updated. | 
| S  | Total number of CPU-seconds used by the system on behalf of the process (in kernel mode), in seconds.                                                                                                                                          | 
| U  | Total number of CPU-seconds that the process used directly (in user mode), in seconds.                                                                                                                                                         | 
| W  | Number of times the process was swapped out of main memory.                                                                                                                                                                                    | 
| X  | Average amount of shared text in the process, in Kilobytes.                                                                                                                                                                                    | 
| Z  | System's page size, in bytes.  This is a per-system constant, but varies between systems.                                                                                                                                                      | 
| c  | Number of times the process was context-switched involuntarily (because the time slice expired).                                                                                                                                               | 
| e  | Elapsed real (wall clock) time used by the process, in seconds.                                                                                                                                                                                | 
| k  | Number of signals delivered to the process.                                                                                                                                                                                                    | 
| p  | Average unshared stack size of the process, in Kilobytes.                                                                                                                                                                                      | 
| r  | Number of socket messages received by the process.                                                                                                                                                                                             | 
| s  | Number of socket messages sent by the process.                                                                                                                                                                                                 | 
| t  | Average resident set size of the process, in Kilobytes.                                                                                                                                                                                        | 
| w  | Number of times that the program was context-switched voluntarily, for instance while waiting for an I/O operation to complete.                                                                                                                | 
| x  | Exit status of the command.                                                                                                                                                                                                                    
(this table from manpage of  time)

You can register the format in the environment variable $ TIME or specify the format with -f option.

export TIME="time result\ncmd:%C\nreal %es\nuser %Us \nsys  %Ss \nmemory:%MKB \ncpu %P"

or

time -f "time result\ncmd:%C\nreal %es\nuser %Us \nsys  %Ss \nmemory:%MKB \ncpu %P" <command>

Execution result (running and check sleep command)

$ /usr/bin/time sleep 1
time result
cmd:sleep 1
real 1.00s
user 0.00s 
sys  0.00s 
memory:2128KB 
cpu 0%

Decompiling Kotlin's program: Data class

yuyabu — Fri, 05 Apr 2019 09:26:39 +0000

If you are a Java programmer you may be tired of having troublesome implementation of setter, getter, hashcode, toString once.

Does not the IDE implement it automatically, or use a tool like lombok not to think deeply about this problem?

In Kotlin, there is a mechanism to automatically generate these troublesome declarations by attaching the qualifier "data" at the position of Class declaration

This is sample of Data Class (Person class).

data class Person (val name: String, val age: Int)

This is how to use person class.

    var bob = Person ("Bob", 33)
    var bob 2 = Person ("Bob", 33)
    println (bob === bob2) // false
    println (bob == bob2) // true
    println (bob.equals (bob2)) // true
    println (bob.hashCode ()) // 2075948
    println (bob.toString ()) // Person (name = Bob, age = 33)

Decompile with JAD

Decompile the person class and convert the automatically implemented code to Java

$ jad Person.class
Parsing Person.class ... Generating Person.jad
Could not fully decompile method hashCode

The method of hashcode could not be decompiled.
I'll check hashcode() at next post.

Decompiling result of java: Person class

import kotlin.jvm.internal.Intrinsics;

public final class Person
{

    public final String getName ()
    {
        return name;
    }

    public final int getAge ()
    {
        return age;
    }

    public Person (String name, int age)
    {
        Intrinsics.checkParameterIsNotNull (name, "name");
        super ();
        this.name = name;
        this.age = age;
    }

    public final String component 1 ()
    {
        return name;
    }

    public final int component 2 ()
    {
        return age;
    }

    public final Person copy (String name, int age)
    {
        Intrinsics.checkParameterIsNotNull (name, "name");
        return new Person (name, age);
    }

    public static volatile Person copy $ default (Person person, String s, int i, int j, Object obj)
    {
        if ((j & 1)! = 0)
            s = person.name;
        if ((j & 2)! = 0)
            i = person.age;
        return person.copy (s, i);
    }

    public String toString ()
    {
        append ("age ="). append (age). append (")"). toString (); return (new StringBuilder ()). append ("Person (name =
    }

    public int hashCode ()
    {
        name;
        if (name == null) goto _ L 2; else goto _ L 1
_L1:
        hashCode ();
          goto _ L 3
_L2:
        JVM INSTR pop;
        false;
_L3:
        31;
        JVM INSTR imul;
        age;
        JVM INSTR iadd;
        return;
    }

    public boolean equals (Object obj)
    {
label0:
        {
            if (this! = obj)
            {
                if (! (obj instance of Person))
                    break label 0;
                Person person = (Person) obj;
                if (! Intrinsics.areEqual (name, person.name) || (age! = person.age))
                    break label 0;
            }
            return true;
        }
        return false;
    }

    private final String name;
    private final int age;
}

Now, we checked automatic generation of hashCode, equals, toString, copy, # copy methods.
Next time,I check hashcode's bytecode.

thank you for your reading.

How to use Caps Lock key as ESC on ubuntu 18

yuyabu — Wed, 27 Feb 2019 17:00:50 +0000

You should replace Caps Lock key for the following reasons.

1.Caps Lock key easy to push from home position.
2.Nowadays, We need few time to use Caps Lock.
3.if Push ESC key from home position, you will use vim more usefull.

Lets try.

1.get gnome-tweak-tool

sudo apt install gnome-tweak-tool

2.start gnome-tweak-tool.

Select "Caps Lock behavior" with "Make Caps Lock an additional ESC"

3.Restart ubuntu.

The setup procedure is over.
Now, your Caps Lock key is ESC.

thanks reading my post.

Decompile and dissasemble JVM bytecode compiled from Kotlin source code

yuyabu — Fri, 08 Feb 2019 04:19:32 +0000

This is an experiment to try using javap (disassembler) and jad (decompiler) for this Kotlin code.

fun main (args: Array <String>) {
    println ("Hello, World!")
}

Code source
https://kotlinlang.org/docs/tutorials/command-line.html

Like other JVM languages, Kotlin is compiled into a class file executable as Java.
We can verify it because javap can display the mnemonic of JVM and decompile as java source code with jad.

Compile this.

kotlinc hello.kt -include-runtime -d hello.jar

Extract jar and use javap, jad for hello.class

jar xf hello.jar

Environment

macOS High Sierra 10

javap (Disassembler)

Preparation

It is unnecessary since it is in the JDK from the beginning

Execution

javap - c HelloKt.class

Result

Compiled from "hello.kt"
public final class HelloKt {
  public static final void main (java.lang.String []);
    Code:
       0: aload_ 0
       1: ldc # 9 // String args
       3: invokestatic # 15 // Method kotlin / jvm / internal / Intrinsics.checkParameterIsNotNull: (Ljava / lang / Object; Ljava / lang / String;) V
       6: ldc # 17 // String Hello, World!
       8: astore_1
       9: getstatic # 23 // Field java / lang / System.out: Ljava / io / PrintStream;
      12: aload_1
      13: invokevirtual # 29 // Method java / io / PrintStream.println: (Ljava / lang / Object;) V
      16: return
}

jad (decompiler)

Preparation

How to introduce jad

brew tap caskroom / cask
brew install caskroom / cask / jad

Execution

You can display the mnemonic as a comment with the -a option.

Command

$ jad -a HelloKt.class
$ cat HelloKt.jad

import java.io.PrintStream;
import kotlin.jvm.internal.Intrinsics;

public final class HelloKt
{

    public static final void main (String args [])
    {
        Intrinsics.checkParameterIsNotNull (args, "args");
    // 0 0: aload_ 0
    // 1 1: ldc 1 # 9 <String "args">
    // 2 3: invokestatic # 15 <Method void Intrinsics.checkParameterIsNotNull (Object, String)>
        String s = "Hello, World!";
    // 3 6: ldc 1 # 17 <String "Hello, World!">
    // 4 8: astore_ 1
        System.out.println (s);
    // 5 9: getstatic # 23 <Field PrintStream System.out>
    // 6 12: aload - 1
    // 7 13: invokevirtual # 29 <Method void PrintStream.println (Object)>
    // 8 16: return
    }
}

It was easy to introduce and analyze.
I will check how Kotlin specific functions are represented and converted as Java in the future.

How to simplest Turing Machine works on postgreSQL

yuyabu — Thu, 07 Feb 2019 11:28:03 +0000

version

postgres:10.6

postgres=# SELECT version();
 PostgreSQL 10.6 (Ubuntu 10.6-0ubuntu0.18.04.1) on x86_64-pc-linux-gnu, compiled by gcc (Ubuntu 7.3.0-16ubuntu3) 7.3.0, 64-bit

Preface

I found interesting post about SQL is Turing complete.

http://blog.coelho.net/database/2013/08/17/turing-sql-1.html

This site try to emulate Turing machine on SQL.

This is table definition.

CREATE TABLE State(    -- TM states
  sid INTEGER PRIMARY KEY,    -- 0 is always the initial state
  isFinal BOOLEAN NOT NULL,
  sname TEXT UNIQUE NOT NULL -- just for show
);

CREATE TABLE Symbol( -- TM symbols
  cid INTEGER PRIMARY KEY,  -- 0 is always the blank symbol
  cname TEXT UNIQUE NOT NULL
);

CREATE TABLE Transition( -- TM transition function
  sid INTEGER NOT NULL REFERENCES State,     -- initial state
  symbol INTEGER NOT NULL REFERENCES Symbol, -- & symbol
  UNIQUE(sid, symbol),
  new_state INTEGER NOT NULL REFERENCES State,
  new_symbol INTEGER NOT NULL REFERENCES Symbol,
  move INTEGER NOT NULL CHECK(move=-1 OR move=1)
);

CREATE TABLE Tape( -- TM initial tape contents
  tid INTEGER PRIMARY KEY,
  symbol INTEGER REFERENCES Symbol
);

This is execution query.

WITH RECURSIVE running(rid, sid, tape, pos) AS (
  -- first store initial tape contents
  SELECT 0, 0, ARRAY(SELECT symbol FROM Tape ORDER BY tid), 1
  UNION
  -- then proceed to compute iterations
  SELECT p.rid+1, t.new_state,
         -- build updated tape as an array
         p.tape[1:p.pos-1] ||                      -- prefix
           t.new_symbol ||                         -- updated cell
           p.tape[p.pos+1:array_length(p.tape,1)], -- suffix
         -- move cursor position
         p.pos+t.move
  FROM running AS p
  -- get state details, to know whether to stop
  JOIN State AS s ON (p.sid=s.sid)
  -- get corresponding state transition
  JOIN Transition AS t ON (t.sid=p.sid AND
                           -- coalesce defaults to blank
                           t.symbol=COALESCE(p.tape[p.pos],0))
  WHERE -- stop on a final state
        NOT s.isFinal
)
-- just store the computed table
INSERT INTO Run
  SELECT * FROM running;

But It didn't work with queries in that site only.

ERROR:  insert or update on table "run" violates foreign key constraint "run_sid_fkey"
DETAIL:  Key (sid)=(0) is not present in table "state".

Because this post has only the table definition(create statement) and no machine data(insert statement)

So I need data of Turing Machine.

note:I found out later that CTS(Cyclic Tag System) data is written here.
https://wiki.postgresql.org/wiki/Turing_Machine_(with_recursive)

(2,3) Turing machine

This time,I choose most simplest Turing machine called "Wolfram's 2-state 3-symbol Turing machine"

https://www.wolframscience.com/prizes/tm23/technicaldetails.html

This Turing machine has 2 satate({1,2}) and 3 Symbol({2,1,0}).

{state, color} -> {next_state, next_color, offset(header position)}

{1, 2} -> {1, 1, -1},
{1, 1} -> {1, 2, -1},
{1, 0} -> {2, 1, 1 },
{2, 2} -> {1, 0, 1 },
{2, 1} -> {2, 2, 1 },
{2, 0} -> {1, 2, -1}

I check this on paper, and make DB record.

INSERT INTO State VALUES(0,FALSE,1),(1,FALSE,2); 
INSERT INTO Symbol VALUES(0,'0'),(1,'1'),(2,'2');
INSERT INTO Transition VALUES
(0,2,0,1,-1),
(0,1,0,2,-1),
(0,0,1,1, 1),
(1,2,0,0, 1),
(1,1,1,2, 1),
(1,0,0,2,-1)

INSERT INTO Tape VALUES(0,0);

(2,3)Turing machine don't have halt state.

Note that there is no halt state for this Turing machine.

Execution query assumes the existence of a halt state,I need change execution query.

WITH RECURSIVE running(rid, sid, tape, pos) AS (
  -- first store initial tape contents
  SELECT 0, 0, ARRAY(SELECT symbol FROM Tape ORDER BY tid), 1
  UNION
  -- then proceed to compute iterations
  SELECT p.rid+1, t.new_state,
         -- build updated tape as an array
         p.tape[1:p.pos-1] ||                      -- prefix
           t.new_symbol ||                         -- updated cell
           p.tape[p.pos+1:array_length(p.tape,1)], -- suffix
         -- move cursor position
         p.pos+t.move
  FROM running AS p
  -- get state details, to know whether to stop
  JOIN State AS s ON (p.sid=s.sid)
  -- get corresponding state transition
  JOIN Transition AS t ON (t.sid=p.sid AND
                           -- coalesce defaults to blank
                           t.symbol=COALESCE(p.tape[p.pos],0))
  WHERE -- stop on a final state
        --NOT s.isFinal -- There is no halt state.
        NOT p.rid = 100 -- By changing this number 
                        -- you can set the number of generations of cellular automata on tape.
)
-- just store the computed table
INSERT INTO Run
  SELECT * FROM running;

Result

Execution result is here.

rid	sid	tape	pos
0	0	{0}	1
1	1	{1}	2
2	0	{1,2}	1
3	0	{2,2}	0
4	1	{1,2,2}	1
5	1	{2,2,2}	2
6	0	{2,0,2}	3
7	0	{2,0,1}	2
8	1	{2,1,1}	3
9	1	{2,1,2}	4
10	0	{2,1,2,2}	3
...	...	...	...
89	0	{2,2,1,1,2,2,2,1,2,2,1,2}	2
90	0	{2,1,1,1,2,2,2,1,2,2,1,2}	1
91	0	{1,1,1,1,2,2,2,1,2,2,1,2}	0
92	1	{1,1,1,1,1,2,2,2,1,2,2,1,2}	1
93	1	{2,1,1,1,1,2,2,2,1,2,2,1,2}	2
94	1	{2,2,1,1,1,2,2,2,1,2,2,1,2}	3
95	1	{2,2,2,1,1,2,2,2,1,2,2,1,2}	4
96	1	{2,2,2,2,1,2,2,2,1,2,2,1,2}	5
97	1	{2,2,2,2,2,2,2,2,1,2,2,1,2}	6
98	0	{2,2,2,2,2,0,2,2,1,2,2,1,2}	7
99	0	{2,2,2,2,2,0,1,2,1,2,2,1,2}	6
100	1	{2,2,2,2,2,1,1,2,1,2,2,1,2}	7

full version is "result.txt" on my github repository

https://github.com/yuyabu/2state-3color-turing-machine-on-sql

I convert "tape" column to image on this rule.

2 -> orange
1 -> yellowfins
0 -> white

and after all, I made this cell automaton image.

Although the method of complementing the white cell is different, it is misaligned, but it is almost the same image as wolfram's page's.

next time

I'll try to make rule 60. Transition function of rule 60 is on NKS book.

{{1, 2} -> {2, 2, 1}, {1, 1} -> {1, 1, 1}, {1, 0} -> {3, 1, -1}, {2, 2} -> {2,1, 1}, {2, 1} -> {1, 2, 1}, {3, 2} -> {3, 2, -1}, {3, 1} -> {3, 1, -1}, {3, 0} -> {1, 0, 1}}

https://www.wolframscience.com/nks/notes-11-12--rule-60-turing-machines/

This article is translated from my blog post(original is japanese).
http://yuyubu.hatenablog.com/entry/2019/01/15/SQL%E4%B8%8A%E3%81%A72%E7%8A%B6%E6%85%8B3%E8%A8%98%E5%8F%B7%E3%83%81%E3%83%A5%E3%83%BC%E3%83%AA%E3%83%B3%E3%82%B0%E3%83%9E%E3%82%B7%E3%83%B3%E3%82%92%E3%82%A8%E3%83%9F%E3%83%A5%E3%83%AC%E3%83%BC%E3%82%B7

All DEFINITION list of "Transactional Information Systems"

yuyabu — Wed, 06 Feb 2019 04:01:37 +0000

"Transactional Information Systems: Theory, Algorithms, and the Practice of Concurrency Control and Recovery (The Morgan Kaufmann Series in Data Management Systems)" is a nice book to learning transaction theory.This book contain many definitions. So,I made list of that.

DEFINITION	page
2.1 Partial Order	46
2.2 Page Model Transaction	46
2.3 Object Model Transaction	51
3.1 Schedules and Histories	66
3.2 Serial History	67
3.3 Herbrand Semantics of Steps	74
3.4 Herbrand Universe	75
3.5 Schedule Semantics	76
3.6 Final State Equivalence	77
3.7 Reads-From Relation	78
3.8 Final State Serializability	82
3.9 View Equivalence	83
3.10 View Serializability	85
3.11 Monotone Classes of Histories	92
3.12 Conflicts and Conflict Relations	93
3.13 Conflict Equivalence	93
3.14 Conflict Serializability	94
3.15 Conflict Graph (Serialization Graph)	96
3.16 Commutativity Based Equivalence	99
3.17 Commutativity Based Reducibility	100
3.18 Order Preservation	102
3.19 Commit Order Preservation	102
3.20 Closure Properties of Schedule Properties	106
3.21 Commit Serializability	107
3.22 Indivisible Units	111
3.23 Dependence of Steps	113
3.24 Relatively Serial Schedule	113
3.25 Relative Serializability	114
3.26 Push Forward and Pull Backward	116
3.27 Relative Serialization Graph	116
4.1 CSR Safety	130
4.2 Two-Phase Locking (2PL)	134
4.3 Conservative 2PL	142
4.4 Strict 2PL	143
4.5 Strong 2PL	144
5.1 Version Function	187
5.2 Multiversion Schedule	188
5.3 Monoversion Schedule	189
5.4 Reads-From Relation	190
5.5 View Equivalence	191
5.6 Multiversion View Serializability	192
5.7 Version Order	194
5.8 Multiversion Serialization Graph (MVSG)	195
5.9 Multiversion Conflict	197
5.10 Multiversion Reducibility	198
5.11 Multiversion Conflict Serializability	199
5.12 Multiversion Conflict Graph	199
6.1 Object Model History	218
6.2 Tree-Consistent Node Ordering	219
6.3 Object Model Schedule	219
6.4 Serial Object Model Schedule	221
6.5 Isolated Subtree	221
6.6 Layered History and Schedule	222
6.7 Flat Object Schedule	223
6.8 Commutative Operations	224
6.9 Commutativity Based Reducibility	226
6.10 Conflict Equivalence and Conflict Serializability	227
6.11 Tree-Reducible History	229
6.12 Level-to-Level Schedule	234
6.13 Conflict Faithfulness	238
6.14 State-Dependent Commutativity	241
6.15 Return Value Commutativity	242
8.1 IDM Transaction	286
8.2 Transaction Equivalence	287
8.3 Final State Serializability	289
8.4 Conflict Serializability	291
8.5 Conflict Graph	291
8.6 Extended Conflict Graph and Serializability	293
8.7 State Serializability	296
8.8 Transaction Chopping	302
8.9 Chopping Graph	302
8.10 Correct Chopping	304
10.1 Isolation Levels	361
10.2 Multiversion Read Committed and Snapshot Isolation Levels	362
10.3 Formal Definition of Snapshot Isolation	363
10.4 Snapshot Isolation Serialization Graph	363
11.1 Expansion of a Schedule	384
11.2 Expanded Conflict Serializability	385
11.3 Reducibility	387
11.4 Prefix Reducibility	389
11.5 Recoverability	391
11.6 Avoiding Cascading Aborts	392
11.7 Strictness	393
11.8 Rigorousness	394
11.9 Log Recoverability	398
11.10 Inverse Operation	408
11.11 Perfect Commutativity	411
11.12 Perfect Closure	413
11.13 Normal Commutativity Table	414
11.14 Strictness	415
11.15 Terminated Subtransactions	416
11.16 Expanded Object Model Schedule	417
11.17 Extended Tree Reducibility	418
12.1 Extended History	434
12.2 Stable Log	435
12.3 Log Buffer	435
12.4 Cached Database	436
12.5 Stable Database	437
12.6 Correct Crash Recovery	437
12.7 Logging Rules: Redo Rule, Undo Rule, Garbage Collection Rule	438
18.1 Global History	677
18.2 Conflict Serializability	678
18.3 Global History	692
18.4 Direct and Indirect Conflict	694
18.5 Global Conflict Graph	695
18.6 Commit-Deferred Transaction	699
18.7 Extended Commitment Ordering	701

https://www.amazon.com/dp/1558605088
https://www.elsevier.com/books/transactional-information-systems/weikum/978-1-55860-508-4

This article is translated from my blog post(original is japanese).
http://yuyubu.hatenablog.com/entry/2019/02/05/weikum%E6%9C%AC%E3%81%AB%E8%A8%98%E8%BC%89%E3%81%95%E3%82%8C%E3%81%A6%E3%81%84%E3%82%8B%E5%85%A8%E5%AE%9A%E7%BE%A9%E3%81%AE%E4%B8%80%E8%A6%A7%E3%83%AA%E3%82%B9%E3%83%88

I try to build and run new dev.to iOS App

yuyabu — Tue, 13 Nov 2018 17:34:36 +0000

DEV now has an iPhone app.

Very much still a work in progress, but they say if you’re not embarrassed by your first version, you waited too long. Right?

Let me know what you think:https://t.co/CgWzdSuWtp pic.twitter.com/RDG1z8WlYO
— Ben Halpern 🤗 (@bendhalpern) 2018年11月10日

https://github.com/thepracticaldev/DEV-ios/

I tried to build and run this app.

clone repository, and push run button on Xcode.

ops! build err. I need "PushNotifications"

I read READ.MD, there is information how to build app.

Fork and clone the project.
Install Carthage. If you use Homebrew then you can install Carthage by running brew install carthage.
Now run carthage update in the project's root directory.
Build and run the project in XCode.

I Installed Carthage on homebrew, And execute carthage update

After that, "PushNotifications" err was gone.

I run it on iPhone emulator on my Mac.

SQL:How to compare with NULL without "IS NULL" operator

yuyabu — Sun, 11 Nov 2018 21:39:10 +0000

We use IS NULL instead of =for comparison with NULL. This is because there are many RDBMSs that become UNKNOWN if you compare null and value with =.

comparison of some value and null to false
comparison of null and null to true

Some times we want to compare it like that. In such a case we can use the comparison operator IS DISTINCT FROM orIS NOT DISTINCT FROM.

A	B	A = B	A IS NOT DISTINCT FROM B
0	0	true	true
0	1	false	false
0	null	unknown	false
null	null	unknown	true

environment and version

postgres=# SELECT version();
                                                             version                                                              
----------------------------------------------------------------------------------------------------------------------------------
 PostgreSQL 10.1 on x86_64-apple-darwin13.4.0, compiled by Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn), 64-bit
(1 row)

$ sqlite3 --version
3.22.0 2018-01-22 18:45:57 0c55d179733b46d8d0ba4d88e01a25e10677046ee3da1d5b1581e86726f2171d

Example on PostgreSQL

--compare null and value with '='( result is unknown)
postgres=# select null = 4;
 ?column? 
----------

(1 row)

--compare value and value (result is true/false)
postgres=# select 4 = 4;
 ?column? 
----------
 t
(1 row)

--compare null and value with 'IS DISTINCT FROM' operator (result is true/false)
postgres=# select null is distinct from  4;
 ?column? 
----------
 t
(1 row)

-- use 'IS NOT DISTINCT FROM' to check equal
postgres=# select null is not distinct from  4;
 ?column? 
----------
 f
(1 row)

-- You can also compare values and values using 'IS DISTINCT FROM'
postgres=# select 4 is distinct from  4;
 ?column? 
----------
 f
(1 row)

sqlite: Use `IS` instead of `IS DISTINCT FROM`

sqlite can't use IS DISTINCT FROM.

You can compare with IS instead

sqlite> select 4 = 4;
1
sqlite> select 4 is null;
0
sqlite> select 4 is 4;
1
sqlite> select 4 is 5;
0
sqlite> select null is null;
1

other

IS DISTINCT FROM operator in MySQL is <=>

reference

https://modern-sql.com/feature/is-distinct-from
Joe Celko's SQL for Smarties: Advanced SQL Programming(Japanese version) 16. 3 IS [NOT] DISTINCT FROM operator

IoT botnet construction tool "Mirai" was asked in Most famous Japanese information technology examinations

yuyabu — Sun, 21 Oct 2018 14:42:36 +0000

On October 21 2018, I received an information processing engineer exam administered by IPA.

May be that is most famous qualifying examination about software engineer in Japan.

I chose Information Security Specialist Examination(SC)

I found Mirai is asked in that exam.

here is the question

here is translation

Which of the following is malware Mirai's behavior?

A. It exploit vulnerabilities of Web servers that run on IoT devices etc. to spread infections, alter Web pages of Web servers, and perform DDos attacks on specific IP addresses at the date and time they were modified.

B. It exploiting Web server's vulnerability to insert illegal JavaScript into a company's Web page and direct the user who viewed the Web page to an unauthorized Web site

C. When the user erroneously and executes the malware execution file in the PC using the file sharing software, it uploads the information in the PC to the Web site on the Internet and makes it public to an unspecified number of people.

D. Try logging in to the telnet port by generating a random IP address, spreading infection to IoT devices using weak passwords at the time of factory shipment, etc. In accordance with the instructions from the C & C server, DDoS attack it dose.

Answer is D

DEV Community: yuyabu

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Decompile with JAD

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Decompile and dissasemble JVM bytecode compiled from Kotlin source code

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SQL:How to compare with NULL without "IS NULL" operator

environment and version

Example on PostgreSQL

sqlite: Use IS instead of IS DISTINCT FROM

other

reference

IoT botnet construction tool "Mirai" was asked in Most famous Japanese information technology examinations

sqlite: Use `IS` instead of `IS DISTINCT FROM`