Alternative Way to Daemonize Java Applications on Systemd (CentOS7/RHEL7)

11/07/2014
Source: http://ae.koroglu.org/alternative-way-to-daemonize-java-applications-on-systemd-centos7rhel7/

I already explained how to daemonize java applications on SysV-style system in here. Since CentOS7/RHEL7 comes with Systemd which is a system and service manager for Linux we migrate old init script to the new system.
Again we’ll use our best budy Daemonize but this time we gonna compile it from source because although it’s signed as approved on fedora package db, Daemonize is not in EPEL7 repository for now. I’ll not going to details how to compile install etc. but I assume that you installed daemonize into /usr/local/sbin
So we need to create two files /etc/sysconfig/fixtures and /lib/systemd/system/fixtures.service
This 1st file is where we define java releated variables such as user, java path, arguments, log files etc..
/etc/sysconfig/fixtures
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# Configz for fixtures service
 
JAVA_USER="pronet"
JAVA_STDOUT="/var/log/pronet/fixtures.log"
JAVA_STDERR="/var/log/pronet/fixtures-error.log"
JAVA_BIN="/usr/java/jdk1.7.0_71/bin/java"
JAVA_APPDIR="/opt/pronet/fixtures"
ARG1="-Dfile.encoding=UTF-8 -Dproject.properties=/opt/pronet/fixtures/fixtures.properties"
ARG2="-Dlog4j.configuration=file:/opt/pronet/fixtures/fixtures-log.properties"
ARG3="-jar /opt/pronet/fixtures/fixtures.jar"
2nd file is service file for fixtures where we define systemd releted variables. There are plenty of documents in Freedesktop Systemd wiki, if you want to know more about I advice you to read them. But roughly unit: consist information about a service, a socket, a device etc, service: information about a process controlled and supervised by systemd and install: installation information for the unit
/lib/systemd/system/fixtures.service
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[Unit]
Description=Fixtures Service
After=syslog.target
After=network.target
 
[Service]
Type=forking
EnvironmentFile=-/etc/sysconfig/fixtures
ExecStart=/usr/local/sbin/daemonize -u $JAVA_USER -o $JAVA_STDOUT -e $JAVA_STDERR -c $JAVA_APPDIR $JAVA_BIN $ARG1 $ARG2 $ARG3
ExecStop=/bin/kill -TERM $MAINPID
TimeoutSec=300
 
[Install]
WantedBy=multi-user.target
Let’s start and stop the service
[root@Srv25 pronet]# systemctl start fixtures
[root@Srv25 pronet]# systemctl stop fixtures
if there is something wrong all service files and docker containers insert data into the systemd journal and we can read the journal :)
[root@Srv25 pronet]# journalctl -u fixtures.service
Checking the service status
[root@Srv25 pronet]# systemctl status fixtures
fixtures.service - Fixtures Service
   Loaded: loaded (/usr/lib/systemd/system/fixtures.service; disabled)
   Active: active (running) since Wed 2014-10-29 21:21:49 EET; 13min ago
 Main PID: 28859 (java)
   CGroup: /system.slice/fixtures.service
           └─28859 /usr/java/jdk1.7.0_71/bin/java -Dfile.encoding=UTF-8 -Dproject.properties=/opt/pronet/fixtures/fixtures.properties -Dlog4j.configuration=file:...
 
Oct 29 21:21:49 Srv25 systemd[1]: Started Fixtures Service.
Enable a service to be started on bootup
[root@Srv25 pronet]# systemctl enable fixtures.service
ln -s '/usr/lib/systemd/system/fixtures.service' '/etc/systemd/system/multi-user.target.wants/fixtures.service'
[root@Srv25 pronet]#
So that’s how it works..

How to select the first/least/max row per group in SQL

10/20/2014
Here are some common SQL problems, all of which have related solutions: how do I find the most recent log entry for each program? How do I find the most popular item from each category? How do I find the top score for each player? In general, these types of “select the extreme from each group” queries can be solved with the same techniques. I’ll explain how to do that in this article, including the harder problem of selecting the top N entries, not just the top 1.
This topic is related to numbering rows, which I just wrote about (see my articles about MySQL-specific and generic techniques to assign a number to each row in a group). Therefore I’ll use nearly the same table and data as I used in those articles, with the addition of a price column:
+--------+------------+-------+
| type   | variety    | price |
+--------+------------+-------+
| apple  | gala       |  2.79 | 
| apple  | fuji       |  0.24 | 
| apple  | limbertwig |  2.87 | 
| orange | valencia   |  3.59 | 
| orange | navel      |  9.36 | 
| pear   | bradford   |  6.05 | 
| pear   | bartlett   |  2.14 | 
| cherry | bing       |  2.55 | 
| cherry | chelan     |  6.33 | 
+--------+------------+-------+

Selecting the one maximum row from each group

Let’s say I want to select the most recent log entry for each program, or the most recent changes in an audit table, or something of the sort. This question comes up over and over on IRC channels and mailing lists. I’ll re-phrase the question in terms of fruits. I want to select the cheapest fruit from each type. Here’s the desired result:
+--------+----------+-------+
| type   | variety  | price |
+--------+----------+-------+
| apple  | fuji     |  0.24 | 
| orange | valencia |  3.59 | 
| pear   | bartlett |  2.14 | 
| cherry | bing     |  2.55 | 
+--------+----------+-------+
There are a few common solutions to this problem. All involve two steps: finding the desired value of price, and then selecting the rest of the row based on that.
One common solution is a so-called self-join. Step one is to group the fruits by type (apple, cherry etc) and choose the minimum price:
select type, min(price) as minprice
from fruits
group by type;
+--------+----------+
| type   | minprice |
+--------+----------+
| apple  |     0.24 | 
| cherry |     2.55 | 
| orange |     3.59 | 
| pear   |     2.14 | 
+--------+----------+
Step two is to select the rest of the row by joining these results back to the same table. Since the first query is grouped, it needs to be put into a subquery so it can be joined against the non-grouped table:
select f.type, f.variety, f.price
from (
   select type, min(price) as minprice
   from fruits group by type
) as x inner join fruits as f on f.type = x.type and f.price = x.minprice;
+--------+----------+-------+
| type   | variety  | price |
+--------+----------+-------+
| apple  | fuji     |  0.24 | 
| cherry | bing     |  2.55 | 
| orange | valencia |  3.59 | 
| pear   | bartlett |  2.14 | 
+--------+----------+-------+
Another common way to do this is with a correlated subquery. This can be much less efficient, depending on how good your system’s query optimizer is. You might find it clearer, though.
select type, variety, price
from fruits
where price = (select min(price) from fruits as f where f.type = fruits.type);
+--------+----------+-------+
| type   | variety  | price |
+--------+----------+-------+
| apple  | fuji     |  0.24 | 
| orange | valencia |  3.59 | 
| pear   | bartlett |  2.14 | 
| cherry | bing     |  2.55 | 
+--------+----------+-------+
Both queries are logically equivalent, though they may not perform the same.

Select the top N rows from each group

This is a slightly harder problem to solve. Finding a single row from each group is easy with SQL’s aggregate functions (MIN(), MAX(), and so on). Finding the first several from each group is not possible with that method because aggregate functions only return a single value. Still, it’s possible to do.
Let’s say I want to select the two cheapest fruits from each type. Here’s a first try:
select type, variety, price
from fruits
where price = (select min(price) from fruits as f where f.type = fruits.type)
   or price = (select min(price) from fruits as f where f.type = fruits.type
      and price > (select min(price) from fruits as f2 where f2.type = fruits.type));
+--------+----------+-------+
| type   | variety  | price |
+--------+----------+-------+
| apple  | gala     |  2.79 | 
| apple  | fuji     |  0.24 | 
| orange | valencia |  3.59 | 
| orange | navel    |  9.36 | 
| pear   | bradford |  6.05 | 
| pear   | bartlett |  2.14 | 
| cherry | bing     |  2.55 | 
| cherry | chelan   |  6.33 | 
+--------+----------+-------+
Yuck! That can be written as a self-join, but it’s just as bad (I leave it as an exercise for the reader). This gets worse as you go to higher numbers (top 3, top 4…). There are other ways to phrase the statement, but they all boil down to the same thing, and they’re all pretty unwieldy and inefficient.
There’s a better way: select the variety from each type where the variety is no more than the second-cheapest of that type.
select type, variety, price
from fruits
where (
   select count(*) from fruits as f
   where f.type = fruits.type and f.price <= fruits.price
) <= 2;
This is elegant, and lets you vary N without rewriting your query (a very good thing!), but it’s functionally the same as the previous query. Both are essentially a quadratic algorithm relative to the number of varieties in each type. And again, some query optimizers may not do well with this and make it quadratic with respect to the number of rows in the table overall (especially if no useful index is defined), and the server might get clobbered. Are there better ways? Can it be done with one pass through the data, instead of the many passes required by a correlated subquery? You know it can, or I wouldn’t be writing this, now would I?

Use UNION

If there’s an index on (type, price), and there are many more records to eliminate than to include in each group, a more efficient single-pass method (especially for MySQL, but also for some other RDBMSs) is to break the queries out separately and put a limit on each, then UNION them all back together. Here’s the syntax you need for MySQL:
(select * from fruits where type = 'apple' order by price limit 2)
union all
(select * from fruits where type = 'orange' order by price limit 2)
union all
(select * from fruits where type = 'pear' order by price limit 2)
union all
(select * from fruits where type = 'cherry' order by price limit 2)
Peter Zaitsev has written in detail about this technique, so I won’t go into it too much more here. If it suits your purposes, it can be a very good solution.
One note: use UNION ALL, not just UNION. It prevents the server sorting the results to eliminate duplicates before returning them. In this case there will be no duplicates, so I’m telling the server to skip that (useless, expensive) step.

Do it with user variables on MySQL

The UNION trick is an especially good idea when the results are a small fraction of the rows in the table and there is an index that can be used for sorting the rows. Another linear-time technique, which might be a good option in cases where you are selecting most of the rows from the table anyway, is user variables. This is MySQL-specific. Please refer to my previous post on how to number rows in MySQL for the gory details of why this works:
set @num := 0, @type := '';

select type, variety, price
from (
   select type, variety, price,
      @num := if(@type = type, @num + 1, 1) as row_number,
      @type := type as dummy
  from fruits
  order by type, price
) as x where x.row_number <= 2;
This isn’t one pass through the table, by the way. The subquery is implemented as a temporary table behind the scenes, so filling it with data is one pass; then selecting every row from it and applying the WHERE clause is another. However, twice through is still O(n) with respect to the table size. That’s a lot better than correlated subqueries, which are O(n2) with respect to the group size – even moderate group sizes cause bad performance (say there are five varieties of each fruit. That’s on the order of 25 passes through the table, all told).

One-pass technique on MySQL… maybe?

If you want to leave your queries up the the query optimizer’s whims, you can try this technique, which builds no temporary tables and makes just one pass through:
set @num := 0, @type := '';

select type, variety, price,
      @num := if(@type = type, @num + 1, 1) as row_number,
      @type := type as dummy
from fruits
group by type, price, variety
having row_number <= 2;
This theoretically ought to work if MySQL orders by the GROUP BY criteria, which it sometimes does for efficiency and to produce the expected results. Does it work? Here’s what it returns on MySQL 5.0.27 on Windows:
+--------+----------+-------+------------+--------+
| type   | variety  | price | row_number | dummy  |
+--------+----------+-------+------------+--------+
| apple  | gala     |  2.79 |          1 | apple  |
| apple  | fuji     |  0.24 |          3 | apple  |
| orange | valencia |  3.59 |          1 | orange |
| orange | navel    |  9.36 |          3 | orange |
| pear   | bradford |  6.05 |          1 | pear   |
| pear   | bartlett |  2.14 |          3 | pear   |
| cherry | bing     |  2.55 |          1 | cherry |
| cherry | chelan   |  6.33 |          3 | cherry |
+--------+----------+-------+------------+--------+
Look closely… it’s returning rows one and three from each group, and they’re not numbered in order of increasing price? Huh? But the HAVING clause says the row_number should be no greater than 2! Here’s what it returns on version 5.0.24a on Ubuntu:
+--------+------------+-------+------------+--------+
| type   | variety    | price | row_number | dummy  |
+--------+------------+-------+------------+--------+
| apple  | fuji       |  0.24 |          1 | apple  |
| apple  | gala       |  2.79 |          1 | apple  |
| apple  | limbertwig |  2.87 |          1 | apple  |
| cherry | bing       |  2.55 |          1 | cherry |
| cherry | chelan     |  6.33 |          1 | cherry |
| orange | valencia   |  3.59 |          1 | orange |
| orange | navel      |  9.36 |          1 | orange |
| pear   | bartlett   |  2.14 |          1 | pear   |
| pear   | bradford   |  6.05 |          1 | pear   |
+--------+------------+-------+------------+--------+
Look, this time everything is numbered 1 and every row is returned. Wonky. This is exactly what the MySQL manual page on user variables warns about.
This technique is pretty much non-deterministic, because it relies on things that you and I don’t get to control directly, such as which indexes MySQL decides to use for grouping. However, if you need to use it – and I know there are some folks out there who do, because I’ve consulted for them – you can still tweak it. We’re getting into the realm of really bastardizing SQL, but the results above came from a table without indexes other than the primary key on (type, variety). What happens if I add an index MySQL can use for grouping?
alter table fruits add key(type, price);
Nothing changes, and EXPLAIN shows why: the query doesn’t use the index I just added. Why? Because the grouping is on three columns, and the index is only on two. In fact, the query is using a temp table and filesort anyway, so this is still not achieving the once-through goal. I can force it to use the index:
set @num := 0, @type := '';

select type, variety, price,
      @num := if(@type = type, @num + 1, 1) as row_number,
      @type := type as dummy
from fruits force index(type)
group by type, price, variety
having row_number <= 2;
Let’s see if that works:
+--------+----------+-------+------------+--------+
| type   | variety  | price | row_number | dummy  |
+--------+----------+-------+------------+--------+
| apple  | fuji     |  0.24 |          1 | apple  | 
| apple  | gala     |  2.79 |          2 | apple  | 
| cherry | bing     |  2.55 |          1 | cherry | 
| cherry | chelan   |  6.33 |          2 | cherry | 
| orange | valencia |  3.59 |          1 | orange | 
| orange | navel    |  9.36 |          2 | orange | 
| pear   | bartlett |  2.14 |          1 | pear   | 
| pear   | bradford |  6.05 |          2 | pear   | 
+--------+----------+-------+------------+--------+
Ah, now we’re cooking! It did what I wanted, without a filesort or temporary table. Another way to do this, by the way, is to take variety out of the GROUP BY so it uses the index on its own. Because this selects a non-grouped column from a grouped query, this only works if you are running with ONLY_FULL_GROUP_BY mode turned off, which I hope you are not doing without good reason.


Source: http://www.xaprb.com/blog/2006/12/07/how-to-select-the-firstleastmax-row-per-group-in-sql/

Improved Persistent Login Cookie Best Practice

  1. When the user successfully logs in with Remember Me checked, a login cookie is issued in addition to the standard session management cookie.
  2. The login cookie contains the user's username, a series identifier, and a token. The series and token are unguessable random numbers from a suitably large space. All three are stored together in a database table.
  3. When a non-logged-in user visits the site and presents a login cookie, the username, series, and token are looked up in the database.
    1. If the triplet is present, the user is considered authenticated. The used token is removed from the database. A new token is generated, stored in database with the username and the same series identifier, and a new login cookie containing all three is issued to the user.
    2. If the username and series are present but the token does not match, a theft is assumed. The user receives a strongly worded warning and all of the user's remembered sessions are deleted.
    3. If the username and series are not present, the login cookie is ignored.

ДЕРЕВО

10/14/2014
Не зважаючи на завантаженість, купу проблем, курс гривні і на те, що начальник – підарас, знайдіть якусь хвилину часу, поїдьте на Видубичі і просто поговоріть з деревами… Ні, я не йопнувся…
Просто підійдіть і скажіть дереву: “Привіт, дерево! Ти пожовкло вже…” - Да, відповість дерево, - бо осінь, і Покрова”…. “То нічого”, - скажете ви, - Ти оживеш навесні і знову будеш зелене…” – Я знаю, - відповість дерево, - навесні всі оживають… Хоча не факт. Був у мене дід, він теж так казав, а на Різдво, ні з того - ні з сього впав на землю прямо в сніг… Правда, навколо нього тепер якісь нові дерева наросли, мабуть, онуки… -Мабуть, - скажете ви йому…
А ти знаєш, дерево, що на початку Андріївського узвозу росте стара липа… Її посадив ще, по-моєму, Петро Могила. І досі жива вона… А коло Полтави ростуть дуби Кочубея. Дуже давні… Але – живі… - Та знаю-знаю, відповість дерево… “По-моєму це чистий PR і реклама…” – Я даже про баобаб, чула, - скаже дерево… В Африці росте. То йому даже по тисячі год буває… Ну лічно ніколи не бачила… Баб бачила (вони в церкву приходять) а баобаб – ні… - Може, це якась лєгєнда і їх немає насправді… Може, й лєгенда, - скажете ви йому, щоб не розстраювать… А ти знаєш, дерево, я колись був в Африці і склав вірш про дерева… Який? - запитає дерево… -“Африканські чорні баби сильно люблять баобаби. Там на кожну з чорних баб, припадає баобаб. А українські баби люблять ягоди й гриби”… - Такоє, - відповість дерево… Ліріка… Кстаті, подивись там внизу у мене гриб росте… Красівий такий - червона шапка і білий горошок по ній… Можеш взять, єслі хочеш… - Добре! - скажете ви, - знову ж таки, щоб не розстраювать його…
Ну, пока, дерево! Побачимося навесні… - Пока! Давай побачимся, спасіба що прийшов… З нами рідко балакають, ну ми любимо поболтать вообще-то… Тільки не кажи нікому… - Ні, не скажу… Бувай!
Тепер можна обнять дерево… І навіть поцілувать його в кору… Щоб ніхто не бачив (бо, можуть мінтів визвать)… І пожать йому руку… В смислі лапу... В смислі – гілку…
Цілком можливо, що дерево вам не відповість нічого. Ну, це не важно… Це все-одно допомагає… На цілу зиму…

(С) Vitalii Chepynoga

JVM tweaks

7/31/2014
-Xmx512m
-XX:MaxHeapSize=512m
-XX:MaxPermSize=512M
-XX:+CMSClassUnloadingEnabled

DCEVM - Dynamic Code Evolution VM

When a java developer works, she spends a lot of time reloading the server context.

The Dynamic Code Evolution Virtual Machine (DCE VM) is a modification of the Java HotSpot(TM) VM that allows unlimited redefinition of loaded classes at runtime. The current hotswapping mechanism of the HotSpot(TM) VM allows only changing method bodies. Our enhanced VM allows adding and removing fields and methods as well as changes to the super types of a class.

It is an open source project released under the GPL v2.0 license.


There's a handy plugin for Intellij, that just downloads DCEVM JRE and registers it inside IDE.
Installation is performed with these steps:
  • Install a DCEVM in Intellij as follows: File -> Settings -> Plugins -> search for DCEVM -> Install.
  • Restart the program and see in the Event Log something like that:
    "DCEVM is available for your environment: Would you like to download it?" 
  • Downloading will be performed into something like that: c:\Users\anton\.IntelliJIdea13\config\plugins\DCEVM_JRE
  • Now that we have a DCEVM JRE installed, let’s update the configuration.
  • Edit Tomcat debug configurations by specifying new JRE. 
  • Run/Debug Configurations -> Server tab -> Use alternative JRE: c:\Users\anton\.IntelliJIdea13\config\plugins\DCEVM_JRE
  • Run/Debug Configurations -> Server tab -> "On frame deactivation" –> update classes and resources
Now run the project in debug option and try to changes some classes and wait until the code reloads.

Consider tweaking your JAVA_OPTS as described in this post

Just a good skeleton for a new Scala project

7/22/2014
This project aims to simplify creating a project from scratch.It's simpler than g8 or typesafe activator because it doesn't require any additional tools, just clone, build and run. It provides a simple way to configure:

https://github.com/schastny/skeleton

Originally coded by: https://github.com/fractal