Index: src/docbkx/book.xml =================================================================== --- src/docbkx/book.xml (revision 1146196) +++ src/docbkx/book.xml (working copy) @@ -261,6 +261,17 @@ that includes versioning. Take that into consideration when making your design, as well as block size for the ColumnFamily. +
+ + In-Memory ColumnFamilies + + ColumnFamilies can optionally be defined as in-memory. Data is still persisted to disk, just like any other ColumnFamily. + In-memory blocks have the highest priority in the , but it is not a guarantee that the entire table + will be in memory. + + See HColumnDescriptor for more information. + +
@@ -984,9 +995,19 @@ - - - + + +
+ Block Cache + The Block Cache contains three levels of block priority to allow for scan-resistance and in-memory ColumnFamilies. A block is added with an in-memory + flag if the containing ColumnFamily is defined in-memory, otherwise a block becomes a single access priority. Once a block is accessed again, it changes to multiple access. + This is used to prevent scans from thrashing the cache, adding a least-frequently-used element to the eviction algorithm. Blocks from in-memory ColumnFamilies + are the last to be evicted. + + + For more information, see the LruBlockCache source + +