Motivation

Currently batch updates on page memory level are not implemented in Ignite. Internal structures, such as BPlusTree and FreeList, do not support them. The performance of batch operations (putAll, datastreamer, preloader) can be improved by implementing batch updates on page memory level.

Competitive analysis

Profiling

Profiling the current rebalancing process shows that most of the time spent on working with FreeList and B+ Tree (details).

Process overview

Currently, when updating the batch of cache entries in off-heap, each of them is processed separately. Such update in PageMemory consists of the following steps:

1. Search for key in B+ Tree
2. Store key-value to data page
3. Insert/update key in B+ tree page

To prevent a redundant secondary search in B+ Tree the invoke operation was introduced.

Invoke in B+ Tree

Let's describe the B+ Tree in more detail to understand the need for invoke operation.

The keys of the tree (hashes) are stored on the B+ Tree pages (index pages), the cache key-value itself is stored on data pages. Each item on the index page includes a link to the data page item. In general, a B+ Tree supports find, put and remove operations. For put and remove, you must first find the point of insertion/update/removal. So, cache entry update without invoke operation can look like this:

• Search B+ Tree for link to old key-value (find)
• The old value does not differ in length - a simple value update of key-value on the data page
• The old value differs in length - the link to it changes:
  • Store a new key-value into data page
  • Put B+ Tree key (with "secondary" find) to update link to data page item
  • Remove old key-value from data page

The invoke operation has the following execution scheme:

OffHeapManager.invoke
                |-> BPlusTree.invoke
                |               |
                |               |
                |               |
                |               |-> Invoke.invokeClosure()
                |               |           |-> UpdateClosure.call(foundRow)
                |               |           |                   |- compare entry version
                |               |           |                   |- newRow = create newRow on data page
                |               |           |                   |- treeOp = PUT/REMOVE/NOOP
                |               |           |                  
                |               |           \-> read treeOp -> create operation closure (Put(newRow)/Remove(row))
                |               |
                |               \-> Invoke.found()/notFound() -> exec operation closure
                |
                |
                \-> finishUpdate/finishRemove

Store key-value

Saving a key-value on data page consists of the following operations:

1. Remove a page from FreeList, which has enough space (if there is no such page - allocate a new one)
2. Lock page
3. Write cache entry data
4. Update page counters
5. Unlock page
6. Based on the remaining free space insert page into FreeList

Advantages

The batch will improve:

1. Average insertion time by reducing count of FreeList actions on each data row
2. Average search/update time in B+ Tree

Proposed changes

Implementation should consists of two major related improvements:

1. Batch writing to data pages
2. Batch updates in B+ Tree

Diagram overview

Batch write to data pages

Find the most free page with enough space for data row in FreeList (if there is no such page - allocate new one) and fill it up to the end.

Batch update in B+ Tree

TBD: describe the implementation.

Proposed plan

Overall changes to support batch updates in PageMemory can be divided into following phases.

Phase 1: Batch insert new keys

• Implement insertDataRows operation in FreeList - insert several data rows at once.
• Implement invokeAll operation in BPlusTree: support searching and inserting range of keys.
• Enable batch insertion in preloader (enabled by a special system property).

Phase 2: Batch update existing keys

• InvokeAll operation should support batch update of existing keys.

Phase 3: DataStreamer support

• Add support for batch updates in DataStreamer (isolated updater).

Phase 4: putAll support

• Add support for batch updates in IgniteCache putAll.

Phase 5: MVCC support

• Add support for MVCC (TRANSACTIONAL_SNAPSHOT) cache mode.

Risks and Assumptions

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Discussion Links

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Reference Links

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Tickets