BlockInfo¶

BlockInfo is a metadata of data blocks (stored in MemoryStore or DiskStore).

Creating Instance¶

BlockInfo takes the following to be created:

• StorageLevel
• ClassTag (Scala)
• tellMaster flag

BlockInfo is created when:

• BlockManager is requested to doPut

Block Size¶

BlockInfo knows the size of the block (in bytes).

The size is 0 by default and changes when:

• BlockStoreUpdater is requested to save
• BlockManager is requested to doPutIterator

Reader Count¶

readerCount is the number of times that this block has been locked for reading

readerCount is 0 by default.

readerCount changes back to 0 when:

• BlockInfoManager is requested to remove a block and clear

readerCount is incremented when a read lock is acquired and decreases when the following happens:

• BlockInfoManager is requested to release a lock and releaseAllLocksForTask

Writer Task¶

writerTask attribute is the task ID that owns the write lock for the block or the following:

• -1 for no writers and hence no write lock in use
• -1024 for non-task threads (by a driver thread or by unit test code)

writerTask is assigned a task ID when:

• BlockInfoManager is requested to lockForWriting, unlock, releaseAllLocksForTask, removeBlock, clear