Pool

The pool configuration provides a way to tune the setting used to setup the pooling associated with various other configuration items. For example a Data Source.

The pool tag itself is not used as a top level configuration item but is instead embedded within other tags.

A pool provides a number of configurable parameters:

maxActive controls the maximum number of objects that can be borrowed from the pool at one time. When non-positive, there is no limit to the number of objects that may be active at one time. When maxActive is exceeded, the pool is said to be exhausted. If 'whenExhaustedAction' is 'grow' this value is not used.
maxIdle controls the maximum number of objects that can sit idle in the pool at any time. When negative, there is no limit to the number of objects that may be idle at one time.
whenExhaustedAction specifies the behavior when the pool is exhausted:
- When whenExhaustedAction is 'fail', pool will throw an Exception
- When whenExhaustedAction is 'grow', pool will create a new object and return it(essentially making maxActive meaningless.)
- When whenExhaustedAction is 'block', pool will block (invoke Object.wait until a new or idle object is available. If a positive maxWait value is supplied, the pool will block for at most that many milliseconds, after which an Exception will be thrown. If maxWait is non-positive, the server method will block indefinitely.
When testOnBorrow is set, the pool will attempt to validate each object before it is returned from the pool. Objects that fail to validate will be dropped from the pool, and a different object will be borrowed.
When testOnReturn is set, the pool will attempt to validate each object before it is returned to the pool. Objects that fail to validate will be dropped from the pool.
Optionally, one may configure the pool to examine and possibly evict objects as they sit idle in the pool. This is performed by an "idle object eviction" thread, which runs asychronously. The idle object eviction thread may be configured using the following attributes:
timeBetweenEvictionRunsMillis indicates how long the eviction thread should sleep before "runs" of examining idle objects. When non-positive, no eviction thread will be launched.
minEvictableIdleTimeMillis specifies the minimum amount of time that an object may sit idle in the pool before it is eligible for eviction due to idle time. When non-positive, no object will be dropped from the pool due to idle time alone.
testWhileIdle indicates whether or not idle objects should be validated. Objects that fail to validate will be dropped from the pool.

Namespace

urn:com.cohga.server.pool#1.0

Tags

pool

Properties

Name	Type	Required	Default	Description
maxActive	number	no	8	The maximum number of objects that can be borrowed from the pool at one time. The cap on the total number of active instances from my pool. Use a negative value for an infinite number of instances.
maxIdle	number	no	8	The maximum number of idle connections in the pool. The cap on the number of "idle" instances in the pool. Use a negative value to indicate an unlimited number of idle instances.
maxWait	number	no	1000	The maximum amount of time to wait, in milliseconds, for an object when the pool is exhausted an and whenExhaustedAction is 'block' (otherwise ignored).
minEvictableIdleTimeMillis	number	no	1800000	The minimum number of milliseconds an connection can sit idle in the pool before it is eligible for eviction. Sets the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any). When non-positive, no objects will be evicted from the pool due to idle time alone.
minIdle	number	no	0	The minimum number of idle connections in the pool. Sets the minimum number of objects allowed in the pool before the evictor thread (if active) spawns new objects. (Note no objects are created when: numActive + numIdle >= maxActive).
numTestsPerEvictionRun	number	no	3	The number of idle objects to examine per run within the idle object eviction thread (if any). Sets the max number of objects to examine during each run of the idle object evictor thread (if any). When a negative value is supplied, ceil(numIdle)/abs(numTestsPerEvictionRun) tests will be run. I.e., when the value is -n, roughly one nth of the idle objects will be tested per run.
softMinEvictableIdleTimeMillis	number	no	-1	The minimum number of milliseconds an connection can sit idle in the pool before it is eligible for eviction with the extra condition that at least "minIdle" amount of connections remain in the pool. Sets the minimum amount of time an object may sit idle in the pool before it is eligible for eviction by the idle object evictor (if any), with the extra condition that at least "minIdle" amount of object remain in the pool. When non-positive, no objects will be evicted from the pool due to idle time alone.
testOnBorrow	boolean	no	false	Should the connection be checked for validity when being borrowed from the pool. When true, objects will be validated before being returned to the pool. If the object fails to validate, it will be dropped from the pool, and we will attempt to borrow another.
testOnReturn	boolean	no	false	Should the connection be checked for validity when being returned to the pool. When true, objects will be validated before being returned to the pool.
testWhileIdle	boolean	no	false	Should the connection be checked for validity when just sitting in the pool. When true, objects will be validated by the idle object evictor (if any). If an object fails to validate, it will be dropped from the pool.
timeBetweenEvictionRunsMillis	number	no	-1	Sets the number of milliseconds to sleep between runs of the idle connection evictor. Sets the number of milliseconds to sleep between runs of the idle object evictor thread. When non-positive, no idle object evictor thread will be run.
whenExhaustedAction	'fail', 'grow' or 'block'	no	block	Sets the action to take when the pool is exhausted (the maximum number of "active" objects has been reached)

Sub-tags

None

Content

None

Examples

<pool:pool>
    <minIdle>4</minIdle>
    <maxIdle>8</maxIdle>
    <testOnBorrow>true</testOnBorrow>
    <testOnReturn>false</testOnReturn>
    <testWhileIdle>true</testWhileIdle>
    <timeBetweenEvictionRunsMillis>60000</timeBetweenEvictionRunsMillis>
    <minEvictableIdleTimeMillis>300000</minEvictableIdleTimeMillis>
    <whenExhaustedAction>grow</whenExhaustedAction>
</pool:pool>