CRaC Example Application

Based on github.com/CRaC/example-jetty to experiment with the use of CRaC.

Based on stackabuse.com/working-with-postgresql-in-java for the PostgreSQL integration.

Goal of the Application

This demo application shows a few use-cases:

Provides a HTTP endpoint to load data from zipped CSV files and return the first 100 records.
The data is converted to Java objects, which takes a long time for a large dataset.
After first load of a file, the data is stored in memory, so each new request returns quickly.
A database is used to store the duration of all actions. The stored logs can also be retrieved with the HTTP endpoint.

Related to CRaC:

The database connection is closed before checkpoint, and reopened after restore.
Because the CSV data is stored in memory, it demonstrates that the application returns data immediately in the HTTP calls after restore from checkpoint, as it's not needed to reload from CSV. This is different behaviour compared to starting the application from JAR.

HTTP endpoints:

Results

These are the durations needed for the HTTP endpoints to respond, as logged in the database.

When Started from JAR

duration=11800, description=Handled request for /files/organizations-1000000.csv
duration=8721, description=Data was converted to Java objects from organizations-1000000.csv
duration=3054, description=ZIP was unpacked from organizations-1000000.csv
duration=5197, description=Handled request for /files/organizations-500000.csv
duration=3609, description=Data was converted to Java objects from organizations-500000.csv
duration=1567, description=ZIP was unpacked from organizations-500000.csv
duration=1482, description=Handled request for /files/organizations-100000.csv
duration=1080, description=Data was converted to Java objects from organizations-100000.csv
duration=372, description=ZIP was unpacked from organizations-100000.csv
duration=373, description=Handled request for /files/organizations-10000.csv
duration=309, description=Data was converted to Java objects from organizations-10000.csv
duration=35, description=ZIP was unpacked from organizations-10000.csv
duration=222, description=Handled request for /files/organizations-1000.csv
duration=94, description=Data was converted to Java objects from organizations-1000.csv
duration=7, description=ZIP was unpacked from organizations-1000.csv
duration=0, description=Started from main
duration=0, description====================================================]

When Started from Checkpoint

As unzipping and data conversion to Java objects is was already done before creating the checkpoint, the HTTP endpoint can respond immediately. For the largest file this means a response in 7 milliseconds instead of 11800.

duration=7, description=Handled request for /files/organizations-1000000.csv
duration=7, description=Handled request for /files/organizations-500000.csv
duration=6, description=Handled request for /files/organizations-100000.csv
duration=8, description=Handled request for /files/organizations-10000.csv
duration=15, description=Handled request for /files/organizations-1000.csv
duration=0, description=Reopened DB connection after restore
duration=0, description====================================================

Conclusion

Of course, this time-consuming CSV-reading process is not a typical use-case, but is used here to illustrate how time-consuming processes can be stored in a checkpoint.

Example Test Data

The CSV files located in src/main/resources/data were downloaded from datablist.com.

Requirements for Raspberry Pi

OS and Java

As described on the blog post Running a CRaC Java application on Raspberry Pi - UPDATE.

Raspberry Pi OS, 64-bit, Bookworm edition, released on October 11, 2023.
Azul Zulu Builds of OpenJDK, version 21 with CRaC:

$ sdk install java 21.crac-zulu

PostgreSQL

Install PostgreSQL and create a user cracApp with password crac123, and database crac for the demo application.

$ sudo apt install postgresql
$ sudo su postgres
postgres$ createuser cracApp -P --interactive
# use password crac123
# superuser y
postgres$ psql
postgres=# CREATE DATABASE crac;
postgres=# exit
postgres$ exit
$ exit

Check if PostgreSQL is running, and the port (5432 by default):

$ sudo netstat -plunt |grep postgres
tcp        0      0 127.0.0.1:5432          0.0.0.0:*               LISTEN      20715/postgres
tcp6       0      0 ::1:5432                :::*                    LISTEN      20715/postgres

$ service postgresql status
● postgresql.service - PostgreSQL RDBMS
     Loaded: loaded (/lib/systemd/system/postgresql.service; enabled; preset: enabled)
     Active: active (exited) since Tue 2023-10-17 15:01:28 BST; 7min ago
   Main PID: 20491 (code=exited, status=0/SUCCESS)
        CPU: 3ms

Oct 17 15:01:28 crac systemd[1]: Starting postgresql.service - PostgreSQL RDBMS...
Oct 17 15:01:28 crac systemd[1]: Finished postgresql.service - PostgreSQL RDBMS.

If you want to connect to the database from another PC, you need to allow remote connections from all addresses. This is not secure, and should only be used for test/develop/debug purposes!

$ sudo nano /etc/postgresql/15/main/postgresql.conf

# Add this line
listen_addresses = '*'

$ sudo nano /etc/postgresql/15/main/pg_hba.conf

# Comment this line and add a new one
#host    all             all             127.0.0.1/32            scram-sha-256
host    all             all             all            scram-sha-256

$ sudo service postgresql restart

Create a table to store the logs:

create table app_log
(
    id          integer NOT NULL GENERATED ALWAYS AS IDENTITY (START 1 INCREMENT 1),
    timestamp   timestamp with time zone DEFAULT now(),
    duration    integer NOT NULL,
    description character varying(255),
    CONSTRAINT app_log_pkey PRIMARY KEY (id)
);

Run with CRaC on Raspberry Pi

Get the Project

$ git clone https://github.com/FDelporte/crac-example.git
$ cd crac-example

Build and Initial Run

First Terminal

$ mvn package
$ java -XX:CRaCCheckpointTo=cr -jar target/crac-example.jar

Second Terminal

$ jcmd target/crac-example.jar JDK.checkpoint

In the first terminal, you can see what's happening during the checkpoint creation:

Oct 17, 2023 7:21:29 PM jdk.internal.crac.LoggerContainer info
INFO: Starting checkpoint
17/10/2023 19:21 | ServerManager                       | beforeCheckpoint     | INFO     | Executing beforeCheckpoint
2023-10-17 19:21:29.978:INFO:oejs.AbstractConnector:Attach Listener: Stopped ServerConnector@77a98a6a{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}
17/10/2023 19:21 | DatabaseManager                     | beforeCheckpoint     | INFO     | Executing beforeCheckpoint
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/log4j-api-2.20.0.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/log4j-core-2.20.0.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/checker-qual-3.31.0.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/postgresql-42.6.0.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/crac-1.4.0.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/jetty-io-9.4.51.v20230217.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/jetty-util-9.4.51.v20230217.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/jetty-http-9.4.51.v20230217.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/javax.servlet-api-3.1.0.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/dependency/jetty-server-9.4.51.v20230217.jar is recorded as always available on restore
Oct 17, 2023 7:21:31 PM jdk.internal.crac.LoggerContainer info
INFO: /home/crac/crac-example/target/crac-example.jar is recorded as always available on restore
Killed

Start From Snapshot

$ java -XX:CRaCRestoreFrom=cr

17/10/2023 19:22 | DatabaseManager                     | afterRestore         | INFO     | Executing afterRestore
17/10/2023 19:22 | DatabaseManager                     | initConnection       | WARN     | Setting up database connection
17/10/2023 19:22 | DatabaseManager                     | initConnection       | INFO     | Database connection status: {ApplicationName=PostgreSQL JDBC Driver}
17/10/2023 19:22 | ServerManager                       | afterRestore         | INFO     | Executing afterRestore
2023-10-17 19:22:48.800:INFO:oejs.AbstractConnector:Attach Listener: Started ServerConnector@77a98a6a{HTTP/1.1, (http/1.1)}{0.0.0.0:8080}

Snapshot Files Stored

$ ls -l --human-readable cr/
total 843M
-rw-r--r-- 1 root crac 1.9K Oct 17 19:37 core-13816.img
-rw-r--r-- 1 root crac  624 Oct 17 19:37 core-13817.img
-rw-r--r-- 1 root crac  557 Oct 17 19:37 core-13818.img
-rw-r--r-- 1 root crac  611 Oct 17 19:37 core-13819.img
-rw-r--r-- 1 root crac  598 Oct 17 19:37 core-13820.img
-rw-r--r-- 1 root crac  599 Oct 17 19:37 core-13821.img
-rw-r--r-- 1 root crac  588 Oct 17 19:37 core-13822.img
-rw-r--r-- 1 root crac  625 Oct 17 19:37 core-13823.img
-rw-r--r-- 1 root crac  644 Oct 17 19:37 core-13824.img
-rw-r--r-- 1 root crac  530 Oct 17 19:37 core-13825.img
-rw-r--r-- 1 root crac  583 Oct 17 19:37 core-13826.img
-rw-r--r-- 1 root crac  556 Oct 17 19:37 core-13827.img
-rw-r--r-- 1 root crac  608 Oct 17 19:37 core-13828.img
-rw-r--r-- 1 root crac  605 Oct 17 19:37 core-13829.img
-rw-r--r-- 1 root crac  634 Oct 17 19:37 core-13830.img
-rw-r--r-- 1 root crac  600 Oct 17 19:37 core-13831.img
-rw-r--r-- 1 root crac  560 Oct 17 19:37 core-13832.img
-rw-r--r-- 1 root crac  517 Oct 17 19:37 core-13833.img
-rw-r--r-- 1 root crac  564 Oct 17 19:37 core-13837.img
-rw-r--r-- 1 root crac  567 Oct 17 19:37 core-13838.img
-rw-r--r-- 1 root crac  593 Oct 17 19:37 core-13844.img
-rw-r--r-- 1 root crac  555 Oct 17 19:37 core-13845.img
-rw-r--r-- 1 root crac  699 Oct 17 19:37 core-13846.img
-rw-r--r-- 1 root crac  666 Oct 17 19:37 core-13847.img
-rw-r--r-- 1 root crac  652 Oct 17 19:37 core-13848.img
-rw-r--r-- 1 root crac  667 Oct 17 19:37 core-13849.img
-rw-r--r-- 1 root crac  659 Oct 17 19:37 core-13850.img
-rw-r--r-- 1 root crac  666 Oct 17 19:37 core-13851.img
-rw-r--r-- 1 root crac  667 Oct 17 19:37 core-13852.img
-rw-r--r-- 1 root crac  675 Oct 17 19:37 core-13853.img
-rw-r--r-- 1 root crac  554 Oct 17 19:37 core-13911.img
-rw-r--r-- 1 root crac  520 Oct 17 19:37 core-13913.img
-rw-r--r-- 1 crac crac   26 Oct 17 19:37 cppath
-rw------- 1 crac crac 349K Oct 17 19:37 dump4.log
-rw-r--r-- 1 root crac  224 Oct 17 19:37 fdinfo-2.img
-rw-r--r-- 1 root crac 4.2K Oct 17 19:37 files.img
-rw-r--r-- 1 root crac   18 Oct 17 19:37 fs-13816.img
-rw-r--r-- 1 root crac   36 Oct 17 19:37 ids-13816.img
-rw-r--r-- 1 root crac   46 Oct 17 19:37 inventory.img
-rw-r--r-- 1 root crac 8.1K Oct 17 19:37 mm-13816.img
-rw-r--r-- 1 root crac 6.3K Oct 17 19:37 pagemap-13816.img
-rw-r--r-- 1 root crac 843M Oct 17 19:37 pages-1.img
-rw------- 1 crac crac  32K Oct 17 19:37 perfdata
-rw-r--r-- 1 root crac  119 Oct 17 19:37 pstree.img
-rw-r--r-- 1 root crac   12 Oct 17 19:37 seccomp.img
-rw-r--r-- 1 root crac   57 Oct 17 19:37 stats-dump
-rw-r--r-- 1 root crac   32 Oct 17 19:37 timens-0.img
-rw-r--r-- 1 root crac  196 Oct 17 19:37 tty-info.img

Name		Name	Last commit message	Last commit date
Latest commit History 17 Commits
src/main		src/main
.gitignore		.gitignore
README.md		README.md
pom.xml		pom.xml

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CRaC Example Application

Goal of the Application

Results

When Started from JAR

When Started from Checkpoint

Conclusion

Example Test Data

Requirements for Raspberry Pi

OS and Java

PostgreSQL

Run with CRaC on Raspberry Pi

Get the Project

Build and Initial Run

First Terminal

Second Terminal

Start From Snapshot

Snapshot Files Stored

About

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FDelporte/crac-example

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Repository files navigation

CRaC Example Application

Goal of the Application

Results

When Started from JAR

When Started from Checkpoint

Conclusion

Example Test Data

Requirements for Raspberry Pi

OS and Java

PostgreSQL

Run with CRaC on Raspberry Pi

Get the Project

Build and Initial Run

First Terminal

Second Terminal

Start From Snapshot

Snapshot Files Stored

About

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