Manual Reference Pages - GENEZZO::PUSHHASH::HPHROWBLK (3)
Genezzo::PushHash::HPHRowBlk.pm - a 90% pure virtual class module that
extends hierarchical "push hash" Genezzo::PushHash::hph with Row/Block
methods. These methods facilitate the construction of classes that
manipulate data blocks directly, such as index access methods and
functions that split rows over multiple blocks..
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Like a standard hierarchical pushhash (hph), the HPHRowBlk is a
pushhash built upon a collection of other pushhashes. A push into the
top-level hash is routed into one of the bottom hashes. If the bottom
hashes are full (push fails), the top-level pushhash uses the factory
method to create or obtain a new pushhash. The HPHRowBlk class is
designed to layer on top of hphs built of hash-tied byte block
storage, such as Genezzo::Row::RSBlock.
CONCEPTS and INTERNALS - useful for implementors
A hph is constructed of N pushhash chunks, and the elements of each
chunk are referred to as slices. Typically, one chunk is current
we push into the current chunk until it fills up, at which point
the hph attempts to make a new one. HPHRowBlk is designed to expose
the underlying block mechanism to the uppermost layer of the pushhash.
It provides some additional methods: _make_new_block,
_get_current_block, and _get_block_and_bce, which provide
functionality somewhat similar to _get_current_chunk/_make_new_chunk,
but on a block level, versus individual scalar (packed row)
operations. In addition, these methods short-circuit the hph tree
of pushhashes, making the bottom block operations directly available
to the top hph layer. The penultimate layer of the hph stack (see
Genezzo::Row::RSFile) must implement the internal block access methods
on the bottom pushhash.
create a new block in the current chunk
and return the block number as a rid.
return the block number of the insertion position in the
return an array of the tied block, the buffer cache element
(see Genezzo::BufCa::BufCaElt), and other useful information.
iterate over all the blocks in the HPHRowBlk push hash.
Btree indexes are implemented as a tree of data blocks. Tree
operations directly manipulate the blocks directly, bypassing the hph
mechanisms that typically isolate the persistent tuple storage from
the top layer. See Genezzo::Index::bt3.
When a packed tuple exceeds the size of an individual block, the row
may be split over multiple blocks. The basic semantics of the row
contents is only understood at the uppermost layer, which packs and
interprets tuple data, while the bottommost layer is solely
responsible for storing and accessing scalar byte string data in
persistent storage. The HPHRowBlk methods provide handles into the
basic block storage so the upper layer can split and reconstruct row
data over multiple blocks. See Genezzo::Row::RSTab.
Jeffrey I. Cohen, firstname.lastname@example.org
Copyright (c) 2003, 2004, 2005 Jeffrey I Cohen. All rights reserved.
This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
Address bug reports and comments to: email@example.com
For more information, please visit the Genezzo homepage
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