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20.3. Eviction and Passivation
To ensure that a single copy of an entry remains, either in memory or in a cache store, use passivation in conjunction with eviction.
The primary reason to use passivation instead of a normal cache store is that updating entries require less resources when passivation is in use. This is because passivation does not require an update to the cache store.
20.3.1. Eviction and Passivation Usage
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If the eviction policy caused the eviction of an entry from the cache while passivation is enabled, the following occur as a result:
- A notification regarding the passivated entry is emitted to the cache listeners.
- The evicted entry is stored.
When an attempt to retrieve an evicted entry is made, the entry is lazily loaded into memory from the cache loader. After the entry and its children are loaded, they are removed from the cache loader and a notification regarding the entry's activation is sent to the cache listeners.
20.3.2. Eviction Example when Passivation is Disabled
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The following example indicates the state of the memory and the persistent store during eviction operations with passivation disabled.
| Step | Key in Memory | Key on Disk |
|---|---|---|
Insert keyOne | Memory: keyOne | Disk: keyOne |
Insert keyTwo | Memory: keyOne, keyTwo | Disk: keyOne, keyTwo |
Eviction thread runs, evicts keyOne | Memory: keyTwo | Disk: keyOne, keyTwo |
Read keyOne | Memory: keyOne, keyTwo | Disk: keyOne, keyTwo |
Eviction thread runs, evicts keyTwo | Memory: keyOne | Disk: keyOne, keyTwo |
Remove keyTwo | Memory: keyOne | Disk: keyOne |
20.3.3. Eviction Example when Passivation is Enabled
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The following example indicates the state of the memory and the persistent store during eviction operations with passivation enabled.
| Step | Key in Memory | Key on Disk |
|---|---|---|
Insert keyOne | Memory: keyOne | Disk: |
Insert keyTwo | Memory: keyOne, keyTwo | Disk: |
Eviction thread runs, evicts keyOne | Memory: keyTwo | Disk: keyOne |
Read keyOne | Memory: keyOne, keyTwo | Disk: |
Eviction thread runs, evicts keyTwo | Memory: keyOne | Disk: keyTwo |
Remove keyTwo | Memory: keyOne | Disk: |
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