The document discusses overflow, expiration, and eviction in the context of memory management. It covers expiration concepts such as time to live (TTL) and idle timeout, including use cases and examples in Apache Geode. Additionally, it addresses eviction actions to manage heap memory usage and maintain performance by removing less recently used entries.

1. Everything You Wanted to Know
About Overflow, Expiration
and Eviction
Karen Miller and Barbara Pruijn
September 2018

2. What We'll Cover
1. Expiration
2. Eviction (and Overflow)

3. Expiration is time based.
Expiration

4. Shopping cart expires after 30 minutes
Expiration - Why/When is it used?

5. ● Authentication: token expiration (session
timeout)
● Finance: trade limit order, market data for
risk calculations
● Insurance quote valid for one day
● Travel reservation: book before hold
expires
● Cache to original data store
Expiration - Why/When is it used?
Application Cache DB

6. ● Expiration duration
● Expiration actions (invalidate, destroy)
Expiration - What is it?

7. ● Expiration Types:
○ Time to live (TTL)
■ Entry is not written (put) for x time (read does
not extend life). When entry is written, last
modified timestamp is updated.
○ Idle timeout
■ When entry is read (get), last accessed
timestamp is updated. (only local region)
■ A write (put) also updates the last accessed
timestamp, but it does do this on all regions
for a write.
Expiration - What is it?

8. Create a region:
• statistics-enabled on the region
• the type of expiration and duration
• the action for expiration
Expiration - How is it used?

9. Time To Live example:
gfsh> create region --name=region_ttl --type=REPLICATE
--enable-statistics
--entry-time-to-live-expiration=60
--entry-time-to-live-expiration-action=INVALIDATE
Idle time example:
gfsh> create region --name=region_idle --type=REPLICATE
--enable-statistics
--entry-idle-time-expiration=60
--entry-idle-time-expiration-action=DESTROY
Expiration - gfsh examples

10. ● No fixed time expiration. If you write (TTL) or read
(Idle) to an entry, you reset the timestamp.
● Geode transactions disable expiration on the entries
participating in the transaction to avoid conflicts during
the commit.
● Only one thread per JVM doing the expiration checks
in the background (the scheduler).
● Don’t expire a million entries at once.
Expiration - Things to know

11. Example on github:
https://github.com/apache/geode-examples/tree/master/expiration
Video:
https://www.youtube.com/watch?v=BVzL3U_alXE
Spring expiration example:
https://docs.spring.io/spring-
data/gemfire/docs/2.0.9.RELEASE/reference/html/#bootstrap-annotation-
config-region-expiration
Expiration - Resources

12. Heap memory management
based on quantity of
memory.
Eviction

13. Heap memory accesses: fast
Disk accesses: slow
Garbage collection (GC): worst
case, not just slow, but stopped. . .
Motivation: performance

14. So, for performance, we want all
region data to fit into heap space.
Eviction keeps heap space usage
(for region entries) within limits by
getting rid of not-as-recently-used
entries.

15. Eviction keeps heap space usage below a
configured threshold.
GC

16. 1. percentage of available heap
2. absolute quantity of heap space used
3. quantity of entries
3 Eviction Thresholds

17. Threshold 1: percentage of available heap space
server heap space
75% threshold

18. Threshold 2: absolute quantity of heap space used
server heap space
2 Gbyte threshold

19. Threshold 3: quantity of entries
server heap space

20. 1. overflow to disk
2. local destroy
2 Eviction Actions

21. The key stays in
memory, and the
value overflows to
disk.
Eviction Action: Overflow to Disk
key1 value1
key2 value2
key3 value3

22. Removes the entry from the local
cache. Any redundant copies
remain.
→ inconsistent entries across
the region
Eviction Action: Local Destroy

23. Threshold: percentage of heap space
Eviction action: overflow to disk
Start servers with the threshold specification:
gfsh>start server --name=s1 --eviction-heap-percentage=80
Create the region with the action specification:
gfsh>create region --name=r1 --type=PARTITION
--eviction-action=overflow-to-disk
Configure Eviction

24. Threshold: quantity of heap space used for region
Eviction action: overflow to disk
Create the region with the threshold and the action
specification:
gfsh>create region --name=r2 --type=PARTITION
--eviction-max-memory=1000
--eviction-action=overflow-to-disk
Configure Eviction
units are in Mbytes

25. Threshold: quantity of entries
Eviction action: overflow to disk
Create the region with the action specification:
gfsh>create region --name=r3 --type=PARTITION
--eviction-action=overflow-to-disk
--eviction-entry-count=80000
Configure Eviction

26. QUESTIONS?