EHC ❯ MemoryStore uses ConcurrentHashMap constructor incorrectly

• Type: Bug
• Status: Closed
• Priority: 2 Major
• Resolution: Fixed
• Component/s: ehcache-core
• Labels:

• Assignee: hsingh
• Reporter: amiller
• Created: October 27, 2009
• Votes: 0
• Watchers: 0
• Updated:

  January 17, 2013
• Resolved:

  November 04, 2009

Description

MemoryStore does this:

    map = new ConcurrentHashMap(maximumSize, DEFAULT_LOAD_FACTOR, CONCURRENCY_LEVEL);

expecting the map to be sized sufficiently to hold maximumSize (according to the Javadoc). However, it will resize once you reach maximumSize*DEFAULT_LOAD_FACTOR (assuming uniform hashing). Would be better to size it initially to maximumSize / DEFAULT_LOAD_FACTOR. CHM will actually bump that up to the next 2^n due to its hash function. And an unlucky hash situation can still cause buckets to need a resize separately, but can’t imagine that’s worth worrying about.

Anyhow, would recommend changing to:

    map = new ConcurrentHashMap(maximumSize / DEFAULT_LOAD_FACTOR, DEFAULT_LOAD_FACTOR, CONCURRENCY_LEVEL);

and drop a comment about the rationale by this formula.

Comments

Abhishek Singh 2009-11-04

Fixed, also added a unit test.

Himadri Singh 2009-11-19

InitialCapacityTest covers it.