Database backed coherence cache

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Database backed Coherence cache
Tips, Tricks and Patterns

Alexey Ragozin
...

Power of read-write-backing-map

• Fetching data as needed
• Separation of concerns
• Gracefully handling concurr...

… and challenges

 DB operations are order of magnitude slower
• Less deterministic response time
• Coherence thread ...

TIPS

BinaryEntryStore, did you know?

BinaryEntryStore – an alternative to
CacheLoader / CacheStore interface.
Works with Bi...

When storeAll(…) is called?

 cache.getAll(…)
• loadAll(…) will be called with partition granularity
(since Coherence...

When storeAll(…) is called?

 cache.invokeAll(…)/aggregate(…)
• calling get() on entry will invoke load(…)
(if entry ...

Warming up aggregator

public static void preloadValuesViaReadThrough(Set<BinaryEntry> entries) {
CacheMap backingMap = ...

Why load(…) is called on write?

Case:
• Entry processor is called on set of entries which is
not in cache and assign...

Bulk put with write through

You can use same trick for updates.
1. Pack your values in entry processor.
2. In entry proce...

Using operation bundling
Worker thread 3
Worker Worker Worker ...

Using operation bundling

storeAll(…) with N keys could be called if
 You have at least N concurrent operations
 You hav...

Checking STORE decoration

 Configure cache as “write-behind”
 Put data
 Wait until, STORE decoration become T...

BEHIND SCENES

How it works?

Distributed cache service

backing-map
read-write Internal map

...

How it works?
Distribution and backup of data

Distributed cache service

...

How it works?
get(key)

Distributed cache service

Cache service...

How it works?
get(key)

Distributed cache service

Cache servi...

How it works?
get(key)

Distributed cache service

Backing map...

How it works?
get(key)

Distributed cache service

Backing map is ...

How it works?
get(key)

Distributed cache service

Cache loader ...

How it works?
get(key)

Distributed cache service

Value is loaded...

How it works?
get(key)

Distributed cache service

Backing map is ...

How it works?
get(key)

Distributed cache service

Internal ...

How it works?
get(key)

Distributed cache service

Call to backing...

How it works?
get(key)
update backup
...

How it works?
get(key)
update backup
...

How it works?
put(k,v)

Distributed cache service

Cache servi...

How it works?
put(k,v)

Distributed cache service

Cache ser...

How it works?
put(k,v)

Distributed cache service

Value is ...

How it works?
put(k,v)

Distributed cache service

...

How it works?
put(k,v)

Distributed cache service

Call to backing...

How it works?
put(k,v)

updat...

How it works?
put(k,v)

update backup
...

How it works?
put(k,v)

Distributed cache service

Eventuall...

How it works?
put(k,v)

Distributed cache service

Value is stored...

How it works?
put(k,v)

Distributed cache service

...

How it works?
put(k,v)

...

THREADING

Requests and jobs

Client side:
One method call

putAll(…)

Requests and jobs

Network:
One request for
each member

PutRequest

putAll(…) ...

Requests and jobs

Storage node:
One job per partition
Job

...

Requests and jobs

Problem
 Single API call may produce hundreds of jobs
for worker threads in cluster (limited by
pa...

Requests and jobs

Workarounds
 Huge thread pools
 Request throttling
 By member (one network request at time)
 ...

“UNBREAKABLE CACHE” PATTERN

“Canary” keys

 Canary keys – special keys (one per partitions)
ignored by all cache operations.
 Canary key is insert...

Recovery procedure

 Store object hash code in database
 Using hash you can query database for all keys
belonging to p...

“Unbreakable cache”

read/write-trough + canary keys + recovery
 Key based operations rely on read-through
 Filter based...

Checking “canary” keys

 Option 1
 check “canary” keys
 perform query
 Option 2
 perform query
 check “canar...

Checking “canary” keys

 Option 1
 check “canary” keys
 perform query
 Option 2
 perform query
 check “canar...

“Unbreakable cache”

Motivation
 Incomplete data set would invalidate hundred of hours of
number crunching
 100% compl...

Thank you
http://blog.ragozin.info
- my articles
http://code.google.com/p/gridkit
- my open source code
...

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