e4611d97a1
Thanks to the pair of `CLIENT_ID`/`CREATED_DATE`,
it is possible to know if the lock is expired, already held or can be reacquire.
I think that the pre delete row is unnecessary and redundant with these two columns.
The rows doesn't need to be purged because the number of row in the table is finite and equal to the number of locks.
At worst, the table will be able to be purged by `deleteExpired()`.
I propose to overwrite these two columns at acquire lock time instead of pre delete the row.
So `delete` then `update` or `insert` become `update` or `insert`.
One client held a lock.
- Another client will be able to hold the same lock only if:
1. the row doesn't exist. Done when the first client will call `unlock()`.
2. the lock expire in case of hardware shutdown. Done by "`OR CREATED_DATE<?`" in `updateQuery`.
- The same client will be able to reacquire it only if:
1. the row doesn't exist.
2. the lock is already held by him. Done by "`CLIENT_ID=? OR`" in `updateQuery`.
**Cost with PostgreSQL:**
```
EXPLAIN DELETE FROM INT_LOCK WHERE REGION='DEFAULT' AND LOCK_KEY='FOO' AND CREATED_DATE<'2020-07-14';
Delete on int_lock (cost=0.14..8.17 rows=1 width=6)
-> Index Scan using int_lock_pk on int_lock (cost=0.14..8.17 rows=1 width=6)
Index Cond: (((region)::text = 'DEFAULT'::text) AND (lock_key = 'FOO'::bpchar))
Filter: (created_date < '2020-07-14 00:00:00'::timestamp without time zone)
EXPLAIN UPDATE INT_LOCK SET CREATED_DATE='2020-07-15' WHERE REGION='DEFAULT' AND LOCK_KEY='FOO' AND CLIENT_ID=NULL;
Update on int_lock (cost=0.00..11.40 rows=1 width=520)
-> Result (cost=0.00..11.40 rows=1 width=520)
One-Time Filter: false
-> Seq Scan on int_lock (cost=0.00..11.40 rows=1 width=520)
```
```
EXPLAIN UPDATE INT_LOCK SET CLIENT_ID=NULL, CREATED_DATE='2020-07-15' WHERE REGION='DEFAULT' AND LOCK_KEY='FOO' AND (CLIENT_ID=NULL OR CREATED_DATE<'2020-07-14')
Update on int_lock (cost=0.14..8.17 rows=1 width=372)
-> Index Scan using int_lock_pk on int_lock (cost=0.14..8.17 rows=1 width=372)
Index Cond: (((region)::text = 'DEFAULT'::text) AND (lock_key = 'FOO'::bpchar))
Filter: (created_date < '2020-07-14 00:00:00'::timestamp without time zone)
```
Spring Integration 
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Checking out and Building
To check out the project and build from the source, do the following:
git clone git://github.com/spring-projects/spring-integration.git
cd spring-integration
./gradlew build
NOTE: While Spring Integration runs with Java SE 6 or higher, a Java 8 compiler is required to build the project.
If you encounter out of memory errors during the build, increase an available heap and permgen for Gradle:
GRADLE_OPTS='-XX:MaxPermSize=1024m -Xmx1024m'
To build and install jars into your local Maven cache:
./gradlew install
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./gradlew api
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./gradlew reference
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./gradlew dist
Using Eclipse
To generate Eclipse metadata (.classpath and .project files), do the following:
./gradlew eclipse
Once complete, you may then import the projects into Eclipse as usual:
File -> Import -> Existing projects into workspace
Browse to the 'spring-integration' root directory. All projects should import free of errors.
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To generate IDEA metadata (.iml and .ipr files), do the following:
./gradlew idea
Resources
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