Page Split Research Articles

Editorial: Curriculum options: Being, knowing, and exploring

Imagine school students developing confidence and connectedness, being actively involved in society and autonomous learning, and demonstrating abilities in thinking, using language, managing themselves, relating to others, and participating and contributing. Would society think that schools were achieving the major educational goals? Would they recognise the role of schools in this process? Would parents want to have these abilities measured and reported? Alternatively, are parents and society more concerned with reports, certificates, and grades for achievement in traditional school subjects? Linked to these questions are two for educators: What is the relative importance of the vision, aims, and competencies compared with the importance of subject knowledge, and what should be done about it? It is interesting to analyse The New Zealand Curriculum (Ministry of Education, 2007). The vision and key competencies statements are covered in three pages. The general discussion of learning areas (or subjects) covers about 11 pages. There are eight levels charts, each covering six pages, a total of 48 pages, presenting subject-based achievement objectives. One possible conclusion from this 3:11:48 page split is that the learning areas are nearly four times as important as the vision and competencies, and specific achievement objectives are more than four times as important as the process of and the general learning within each subject. Faced with these weightings, together with the traditions of schooling and the currently accepted emphasis on assessment, only confident teachers are likely to significantly change the focus of their work. It seems the best that might be achieved in curriculum development is that some teachers might make some small changes as they work within subjects to emphasise the vision and the competencies. Even as these teachers make changes, their efforts may be undermined by the assessment regime (school reporting and leaver qualifications) that affects schools. This emphasis on subject outcomes may be exacerbated by the fact that there are no achievement outcomes for competencies. Perhaps this is because assessment has traditionally been concerned with things (recall of facts and simple procedures that are remembered as though they were facts), while competencies are processes (described by verbs)--it is always easier to measure things than processes. From my perspective the current assessment regime serves no educational purpose; indeed, our current assessment is demotivating. It tells students what they do not know and cannot do, rather than what they do know and can do, and it measures the outcomes of learning rather than the process. Assessment could be changed to focus primarily on formative purposes for guidance, and emphasise self-assessment (a desirable metacognitive thinking skill related to learning). Even within existing assessment traditions it is interesting to note how other educational systems emphasise more than traditional school subjects. For example, the French Baccalaureate examination includes a compulsory philosophy examination that focuses on thinking, while the International Baccalaureate Diploma schools include two compulsory subjects--thinking is addressed by theories of knowledge and participation, contribution, and by creative action and service (K. Hara, personal communication, 12 August 2008). During my time in education in New Zealand there have been official curriculum changes every 10 to 15 years, but these changes are only part of the real change process. Lead teachers have always explored possibilities and tried new alternatives, and when their explorations seem to be successful other teachers have followed (and finally the ideas are often accepted at the official level). Currently the Curriculum, with less specificity than its predecessor, is seen as encouraging exploration, though I am concerned that the emphasis on compliance, assessment, and reporting might work against this freedom. …

Path conscious caching of [formula omitted] tree indexes in a shared disks cluster

A shared disks (SD) cluster is a representative architecture to couple multiple computing nodes for high performance transaction processing. Every node in the SD cluster shares a common database at the disk level. To avoid frequent disk accesses, each node caches both data pages and index pages in its local memory buffer. In general, index pages are accessed more often and thus cached at more nodes than their corresponding data pages. Furthermore, tree-based indexes such as B + trees require complicated operations, e.g., root-to-leaf traversal and structure modification operation (SMO) due to a page split or a page concatenation. This means that it is strongly required to devise a dedicated cache coherency scheme (CCS) for index pages that takes advantage of the semantics of their access. In this paper, we propose a new CCS for B + tree indexes in the SD cluster. The proposed scheme can reduce the message traffic between nodes and the number of tree re-traversals. An extensive performance study shows that the proposed scheme exhibits substantial performance improvement over the previous schemes, especially when there are large number of nodes or the update probability is high.

B-tree concurrency control and recovery in page-server database systems

We develop new algorithms for the management of transactions in a page-shipping client-server database system in which the physical database is organized as a sparse B-tree index. Our starvation-free fine-grained locking protocol combines adaptive callbacks with key-range locking and guarantees repeatable-read-level isolation (i.e., serializability) for transactions containing any number of record insertions, record deletions, and key-range scans. Partial and total rollbacks of client transactions are performed by the client. Each structure modification such as a page split or merge is defined as an atomic action that affects only two levels of the B-tree and is logged using a single redo-only log record, so that the modification never needs to be undone during transaction rollback or restart recovery. The steal-and-no-force buffering policy is applied by the server when flushing updated pages onto disk and by the clients when shipping updated data pages to the server, while pages involved in a structure modification are forced to the server when the modification is finished. The server performs the restart recovery from client and system failures using an ARIES/CSA-based recovery protocol. Our algorithms avoid accessing stale data but allow a data page to be updated by one client transaction and read by many other client transactions simultaneously, and updates may migrate from a data page to another in structure modifications caused by other transactions while the updating transaction is still active.

Concurrency control and recovery for balanced B-link trees

In this paper we present new concurrent and recoverable B-link-tree algorithms. Unlike previous algorithms, ours maintain the balance of the B-link tree at all times, so that a logarithmic time bound for a search or an update operation is guaranteed under arbitrary sequences of record insertions and deletions. A database transaction can contain any number of operations of the form “fetch the first (or next) matching record”, “insert a record”, or “delete a record”, where database records are identified by their primary keys. Repeatable-read-level isolation for transactions is guaranteed by key-range locking. The algorithms apply the write-ahead logging (WAL) protocol and the steal and no-force buffering policies for index and data pages. Record inserts and deletes on leaf pages of a B-link tree are logged using physiological redo-undo log records. Each structure modification such as a page split or merge is made an atomic action by keeping the pages involved in the modification latched for the (short) duration of the modification and the logging of that modification; at most two B-link-tree pages are kept X-latched at a time. Each structure modification brings the B-link tree into a structurally consistent and balanced state whenever the tree was structurally consistent and balanced initially. Each structure modification is logged using a single physiological redo-only log record. Thus, a structure modification will never be undone even if the transaction that gave rise to it eventually aborts. In restart recovery, the redo pass of our ARIES-based recovery protocol will always produce a structurally consistent and balanced B-link tree, on which the database updates by backward-rolling transactions can always be undone logically, when a physical (page-oriented) undo is no longer possible.

Linear-density hashing with dynamic overflow sharing

A new method for handling overflow records in a linear hash file is introduced. This method, referred to as dynamic overflow sharing, requires that a small number of contiguous pages in the file be treated as a group for the initial sharing of an overflow page. An increase in the number of overflow records belonging to the group could result in the overflow page itself being split. The resulting two overflow pages are now associated with half the pages in the group. This process of overflow page splitting and reallocation can continue with further growth in the number of records hashing to the group. An important element in dynamic overflow sharing is that pointers to overflow are maintained in the home pages themselves in the form of a small extendible directory. A primary advantage of this method is that it is possible to retrieve any record with a maximum of two disk accesses. In addition, it enables file expansion to be performed at per record access costs which are superior to other recently reported schemes. Dynamic overflow sharing is described and analyzed for two situations: 1. (1) a linear, downward slope load distribution and 2. (2) a uniform load distribution of records in the file. A comparison of the performance in the two cases reveals that, in general, the average retrieval, insertion and storage utilization performance of linear density hashing is superior to uniform density hashing and only slightly worse than conventional (non-dynamic) hashing.

Concurrent operations on extendible hashing and its performance

Extendible hashing is a dynamic data structure which accommodates expansion and contraction of any stored data efficiently. In this article, an algorithm has been developed for managing concurrent operations on extendible hashing by achieving optimal memory utilization by supporting directly expansion and contraction, page split, and merge. The results of this study have been encouraging in the sense that it seems to provide a higher degree of concurrency compared to other algorithms on an extendible hash file.

A Human Factors Design Investigation of a Computerized Layout System of Text-Graphic Technical Materials

In converting task listings into multiple pages of documentation for job aids or training, the two major problems are deciding how much material should go on each page and how text and graphics should be laid out on the page. A questionnaire study was used to collect input from 14 human factors personnel in order to design algorithms for page splitting and page layout. From the rules or heuristics used for page splitting, an algorithm was devised that closely matched human page-splitting results. Layout of individual pages was automated with an algorithm based on the (significant) consensus among the subjects on questions of graphics positioning and label ordering. The two algorithms have been combined in a computer-aided design procedure that automatically pages task lists and lays out individual pages.

Modelling the human factors aspects of a computer-based text-graphics layout system

Abstract In converting task listings into multiple pages of documentation for job aids or training, the two major problems are deciding on how much material should go on each page and how text and graphics should be laid out on the page. A questionnaire study was used to collect input from fourteen human factors personnel in order to design algorithms for page splitting and page layout. From the rules or heuristics used for page-splitting, an algorithm was devised which closely matched human page-splitting results. Layout of individual pages was automated with an algorithm based on the (significant) consensus among the subjects on questions of graphics positioning and label ordering. The two algorithms have been combined in a Computer Aided Design Procedure which automatically pages task lists and lays out individual pages.

Binary trees paging

A dynamic page allocation technique for binary search trees is proposed. The method is based on page splitting, like the B-tree construction procedure, and on balanced bunch allocation into the pages. An analysis of the paged index structure resulting from the proposed allocation technique is performed. Furthermore the resulting index can be considered as a modification of B-trees in order to give a flexible structure to the keys in a page. A comparison with B-trees is then carried on, pointing out the field of application of the proposed approach.