Traditionally
transaction managers have been server programs running as a separate
process on a separate server machine. Atomikos thought otherwise. They
were the first to move towards embeddable transaction management.
This means that transaction manager becomes part of the application,
and is used by instantiating a class and calling its methods. It is
no more a separate process running separately on a server machine.
This means that the problem of connection sharing as described in my
earlier blog,
is no more there. The application and the transaction manager are the
same process so they can easily share the same connection. In order
to demonstrate this capability we will implement the following
example, using PostgreSQL as resource manager and Atomikos as
Transaction Manager.
Assume a bank with
two branches B1 and B2. Assume each branch uses its own PostgreSQL
database server PG1 & PG2. Assume branch B1 has an account A1 &
branch B2 has an account A2. Assume account A1
has balance USD 100 & account A2 has balance 0.
Assume a transfer of
USD 100 is initiated from account A1 to A2 using an application which
uses Atomikos as transaction manager.
The following
diagram shows the detail of the implementation.
The resource Manager:
I used PostgreSQL
9.6.2 on 64 bit CentOS 7. The main changes in the postgresql.conf are
as follows:
max_prepared_transactions
= 100
log_connections = on
log_disconnections =
on
log_line_prefix =
'[%p][%c][%v][%r][%u][%a]'
log_statement =
'all'
In order to run the
test application one has to create user atomikos on both the servers
using:
./createuser -d -l
-s -h localhost -p 5432 atomikos
./createuser -d -l
-s -h localhost -p 9432 atomikos
Here are the details
of the sourcecode. The source code consists of four files.
ResourceManagerSettings.java
– contains the settings of the two PostgreSQL servers I used to
test the application.
TransferApp.java –
the main class that has the doTransfer() method that performs the
balance transfer. In addition this class provides function to set up
table in both the servers and populate them with data that is
required to do the test. This class also provides a function that
tests the transfer.
TestTransfer.java –
test the balance transfer.
pom.xml – each
maven project must have this file that lists all the dependencies.
Finding the dependencies and their latest version was a challenge,
and these two sites helped a lot:
To find jars I used
: findjar.com
and to find the
maven dependency I used : search.maven.org
To run the
application use the following command
mvn install
Note : If this
command gives you errors like JAVA_HOME not set etc please refer to
this tutorial.
This command should
result in the following output:
[INFO]
Scanning for projects...
[INFO]
[INFO]
------------------------------------------------------------------------
[INFO]
Building BalanceTransferApp 1.0.0
[INFO]
------------------------------------------------------------------------
[INFO]
[INFO]
--- maven-resources-plugin:2.6:resources (default-resources) @
BalanceTransferApp ---
[WARNING]
Using platform encoding (UTF-8 actually) to copy filtered resources,
i.e. build is platform dependent!
[INFO]
skip non existing resourceDirectory
/home/user_name/Projects/atomikos/pg/TransferApp/src/main/resources
[INFO]
[INFO]
--- maven-compiler-plugin:3.1:compile (default-compile) @
BalanceTransferApp ---
[INFO]
Changes detected - recompiling the module!
[WARNING]
File encoding has not been set, using platform encoding UTF-8, i.e.
build is platform dependent!
[INFO]
Compiling 2 source files to
/home/user_name/Projects/atomikos/pg/TransferApp/target/classes
[INFO]
[INFO]
--- maven-resources-plugin:2.6:testResources (default-testResources)
@ BalanceTransferApp ---
[WARNING]
Using platform encoding (UTF-8 actually) to copy filtered resources,
i.e. build is platform dependent!
[INFO]
skip non existing resourceDirectory
/home/user_name/Projects/atomikos/pg/TransferApp/src/test/resources
[INFO]
[INFO]
--- maven-compiler-plugin:3.1:testCompile (default-testCompile) @
BalanceTransferApp ---
[INFO]
Changes detected - recompiling the module!
[WARNING]
File encoding has not been set, using platform encoding UTF-8, i.e.
build is platform dependent!
[INFO]
Compiling 1 source file to
/home/user_name/Projects/atomikos/pg/TransferApp/target/test-classes
[INFO]
[INFO]
--- maven-surefire-plugin:2.12.4:test (default-test) @
BalanceTransferApp ---
[INFO]
Surefire report directory:
/home/user_name/Projects/atomikos/pg/TransferApp/target/surefire-reports
-------------------------------------------------------
T
E S T S
-------------------------------------------------------
Running
com.enterprisedb.transferapp.TestTransfer
log4j:WARN
No appenders could be found for logger
(com.atomikos.logging.LoggerFactory).
log4j:WARN
Please initialize the log4j system properly.
Thanks
for using Atomikos! Evaluate
http://www.atomikos.com/Main/ExtremeTransactions for advanced
features and professional support
or
register at http://www.atomikos.com/Main/RegisterYourDownload to
disable this message and receive FREE tips & advice
Tests
run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.777 sec
Results
:
Tests
run: 1, Failures: 0, Errors: 0, Skipped: 0
[INFO]
[INFO]
--- maven-jar-plugin:2.4:jar (default-jar) @ BalanceTransferApp ---
[INFO]
Building jar:
/home/user_name/Projects/atomikos/pg/TransferApp/target/BalanceTransferApp-1.0.0.jar
[INFO]
[INFO]
--- maven-install-plugin:2.4:install (default-install) @
BalanceTransferApp ---
[INFO]
Installing
/home/user_name/Projects/atomikos/pg/TransferApp/target/BalanceTransferApp-1.0.0.jar
to
/home/user_name/.m2/repository/com/enterprisedb/transferapp/BalanceTransferApp/1.0.0/BalanceTransferApp-1.0.0.jar
[INFO]
Installing /home/user_name/Projects/atomikos/pg/TransferApp/pom.xml
to
/home/user_name/.m2/repository/com/enterprisedb/transferapp/BalanceTransferApp/1.0.0/BalanceTransferApp-1.0.0.pom
[INFO]
------------------------------------------------------------------------
[INFO]
BUILD SUCCESS
[INFO]
------------------------------------------------------------------------
[INFO]
Total time: 3.336 s
[INFO]
Finished at: 2017-12-27T17:29:10+05:00
[INFO]
Final Memory: 18M/331M
[INFO]
------------------------------------------------------------------------
The
PostgreSQL log for the first server:
[47837][5a439215.badd][][127.0.0.1(41024)][[unknown]][[unknown]]LOG:
connection received: host=127.0.0.1 port=41024
[47837][5a439215.badd][2/1328][127.0.0.1(41024)][atomikos][[unknown]]LOG:
connection authorized: user=atomikos database=postgres
[47837][5a439215.badd][2/1329][127.0.0.1(41024)][atomikos][[unknown]]LOG:
execute <unnamed>: SET extra_float_digits = 3
[47837][5a439215.badd][2/1330][127.0.0.1(41024)][atomikos][[unknown]]LOG:
execute <unnamed>: SELECT gid FROM pg_prepared_xacts where
database = current_database()
[47838][5a439215.bade][][127.0.0.1(41026)][[unknown]][[unknown]]LOG:
connection received: host=127.0.0.1 port=41026
[47838][5a439215.bade][3/1030][127.0.0.1(41026)][atomikos][[unknown]]LOG:
connection authorized: user=atomikos database=postgres
[47838][5a439215.bade][3/1031][127.0.0.1(41026)][atomikos][[unknown]]LOG:
execute <unnamed>: SET extra_float_digits = 3
[47838][5a439215.bade][3/1032][127.0.0.1(41026)][atomikos][[unknown]]LOG:
execute <unnamed>: DROP TABLE IF EXISTS ACCOUNTS
[47838][5a439215.bade][3/1033][127.0.0.1(41026)][atomikos][[unknown]]LOG:
execute <unnamed>: create table ACCOUNTS(id int, title
varchar(255), balance int)
[47838][5a439215.bade][3/1034][127.0.0.1(41026)][atomikos][[unknown]]LOG:
execute <unnamed>: insert into ACCOUNTS values (1, 'Account
A1', 100)
[47844][5a439215.bae4][][127.0.0.1(41032)][[unknown]][[unknown]]LOG:
connection received: host=127.0.0.1 port=41032
[47844][5a439215.bae4][4/282][127.0.0.1(41032)][atomikos][[unknown]]LOG:
connection authorized: user=atomikos database=postgres
[47844][5a439215.bae4][4/283][127.0.0.1(41032)][atomikos][[unknown]]LOG:
execute <unnamed>: SET extra_float_digits = 3
[47844][5a439215.bae4][4/284][127.0.0.1(41032)][atomikos][[unknown]]LOG:
execute <unnamed>: SELECT gid FROM pg_prepared_xacts where
database = current_database()
[47844][5a439215.bae4][4/285][127.0.0.1(41032)][atomikos][[unknown]]LOG:
execute <unnamed>: BEGIN
[47844][5a439215.bae4][4/285][127.0.0.1(41032)][atomikos][[unknown]]LOG:
execute <unnamed>: update ACCOUNTS set balance = 0 where id =
1
[47844][5a439215.bae4][4/285][127.0.0.1(41032)][atomikos][[unknown]]LOG:
execute <unnamed>: PREPARE TRANSACTION
'1096044365_NTIuNzEuMTg1LjEyNS50bTE1MTQzNzc3NDk2OTAwMDAwMQ==_NTIuNzEuMTg1LjEyNS50bTE='
[47844][5a439215.bae4][4/286][127.0.0.1(41032)][atomikos][[unknown]]LOG:
execute <unnamed>: COMMIT PREPARED
'1096044365_NTIuNzEuMTg1LjEyNS50bTE1MTQzNzc3NDk2OTAwMDAwMQ==_NTIuNzEuMTg1LjEyNS50bTE='
[47838][5a439215.bade][3/1035][127.0.0.1(41026)][atomikos][[unknown]]LOG:
execute <unnamed>: select balance from accounts where id = 1
[47838][5a439215.bade][][127.0.0.1(41026)][atomikos][[unknown]]LOG:
disconnection: session time: 0:00:00.166 user=atomikos
database=postgres host=127.0.0.1 port=41026
[47837][5a439215.badd][][127.0.0.1(41024)][atomikos][[unknown]]LOG:
disconnection: session time: 0:00:00.238 user=atomikos
database=postgres host=127.0.0.1 port=41024
[47844][5a439215.bae4][][127.0.0.1(41032)][atomikos][[unknown]]LOG:
disconnection: session time: 0:00:00.058 user=atomikos
database=postgres host=127.0.0.1 port=41032
The
PostgreSQL log for the second server:
[47840][5a439215.bae0][][127.0.0.1(51134)][[unknown]][[unknown]]LOG:
connection received: host=127.0.0.1 port=51134
[47840][5a439215.bae0][2/607][127.0.0.1(51134)][atomikos][[unknown]]LOG:
connection authorized: user=atomikos database=postgres
[47840][5a439215.bae0][2/608][127.0.0.1(51134)][atomikos][[unknown]]LOG:
execute <unnamed>: SET extra_float_digits = 3
[47840][5a439215.bae0][2/609][127.0.0.1(51134)][atomikos][[unknown]]LOG:
execute <unnamed>: SELECT gid FROM pg_prepared_xacts where
database = current_database()
[47841][5a439215.bae1][][127.0.0.1(51136)][[unknown]][[unknown]]LOG:
connection received: host=127.0.0.1 port=51136
[47841][5a439215.bae1][3/257][127.0.0.1(51136)][atomikos][[unknown]]LOG:
connection authorized: user=atomikos database=postgres
[47841][5a439215.bae1][3/258][127.0.0.1(51136)][atomikos][[unknown]]LOG:
execute <unnamed>: SET extra_float_digits = 3
[47841][5a439215.bae1][3/259][127.0.0.1(51136)][atomikos][[unknown]]LOG:
execute <unnamed>: DROP TABLE IF EXISTS ACCOUNTS
[47841][5a439215.bae1][3/260][127.0.0.1(51136)][atomikos][[unknown]]LOG:
execute <unnamed>: create table ACCOUNTS(id int, title
varchar(255), balance int)
[47841][5a439215.bae1][3/261][127.0.0.1(51136)][atomikos][[unknown]]LOG:
execute <unnamed>: insert into ACCOUNTS values (2, 'Account
A2', 0)
[47845][5a439215.bae5][][127.0.0.1(51140)][[unknown]][[unknown]]LOG:
connection received: host=127.0.0.1 port=51140
[47845][5a439215.bae5][4/174][127.0.0.1(51140)][atomikos][[unknown]]LOG:
connection authorized: user=atomikos database=postgres
[47845][5a439215.bae5][4/175][127.0.0.1(51140)][atomikos][[unknown]]LOG:
execute <unnamed>: SET extra_float_digits = 3
[47845][5a439215.bae5][4/176][127.0.0.1(51140)][atomikos][[unknown]]LOG:
execute <unnamed>: SELECT gid FROM pg_prepared_xacts where
database = current_database()
[47845][5a439215.bae5][4/177][127.0.0.1(51140)][atomikos][[unknown]]LOG:
execute <unnamed>: BEGIN
[47845][5a439215.bae5][4/177][127.0.0.1(51140)][atomikos][[unknown]]LOG:
execute <unnamed>: update ACCOUNTS set balance = 100 where id
= 2
[47845][5a439215.bae5][4/177][127.0.0.1(51140)][atomikos][[unknown]]LOG:
execute <unnamed>: PREPARE TRANSACTION
'1096044365_NTIuNzEuMTg1LjEyNS50bTE1MTQzNzc3NDk2OTAwMDAwMQ==_NTIuNzEuMTg1LjEyNS50bTI='
[47845][5a439215.bae5][4/178][127.0.0.1(51140)][atomikos][[unknown]]LOG:
execute <unnamed>: COMMIT PREPARED
'1096044365_NTIuNzEuMTg1LjEyNS50bTE1MTQzNzc3NDk2OTAwMDAwMQ==_NTIuNzEuMTg1LjEyNS50bTI='
[47841][5a439215.bae1][3/262][127.0.0.1(51136)][atomikos][[unknown]]LOG:
execute <unnamed>: select balance from accounts where id = 2
[47840][5a439215.bae0][][127.0.0.1(51134)][atomikos][[unknown]]LOG:
disconnection: session time: 0:00:00.071 user=atomikos
database=postgres host=127.0.0.1 port=51134
[47841][5a439215.bae1][][127.0.0.1(51136)][atomikos][[unknown]]LOG:
disconnection: session time: 0:00:00.066 user=atomikos
database=postgres host=127.0.0.1 port=51136
[47845][5a439215.bae5][][127.0.0.1(51140)][atomikos][[unknown]]LOG:
disconnection: session time: 0:00:00.040 user=atomikos
database=postgres host=127.0.0.1 port=51140
