1,718,134 research outputs found
B+-tree Index Optimization by Exploiting Internal Parallelism of Flash-based Solid State Drives
Previous research addressed the potential problems of the hard-disk oriented
design of DBMSs of flashSSDs. In this paper, we focus on exploiting potential
benefits of flashSSDs. First, we examine the internal parallelism issues of
flashSSDs by conducting benchmarks to various flashSSDs. Then, we suggest
algorithm-design principles in order to best benefit from the internal
parallelism. We present a new I/O request concept, called psync I/O that can
exploit the internal parallelism of flashSSDs in a single process. Based on
these ideas, we introduce B+-tree optimization methods in order to utilize
internal parallelism. By integrating the results of these methods, we present a
B+-tree variant, PIO B-tree. We confirmed that each optimization method
substantially enhances the index performance. Consequently, PIO B-tree enhanced
B+-tree's insert performance by a factor of up to 16.3, while improving
point-search performance by a factor of 1.2. The range search of PIO B-tree was
up to 5 times faster than that of the B+-tree. Moreover, PIO B-tree
outperformed other flash-aware indexes in various synthetic workloads. We also
confirmed that PIO B-tree outperforms B+-tree in index traces collected inside
the Postgresql DBMS with TPC-C benchmark.Comment: VLDB201
Suffix Tree of Alignment: An Efficient Index for Similar Data
We consider an index data structure for similar strings. The generalized
suffix tree can be a solution for this. The generalized suffix tree of two
strings and is a compacted trie representing all suffixes in and
. It has leaves and can be constructed in time.
However, if the two strings are similar, the generalized suffix tree is not
efficient because it does not exploit the similarity which is usually
represented as an alignment of and .
In this paper we propose a space/time-efficient suffix tree of alignment
which wisely exploits the similarity in an alignment. Our suffix tree for an
alignment of and has leaves where is the sum of
the lengths of all parts of different from and is the sum of the
lengths of some common parts of and . We did not compromise the pattern
search to reduce the space. Our suffix tree can be searched for a pattern
in time where is the number of occurrences of in and
. We also present an efficient algorithm to construct the suffix tree of
alignment. When the suffix tree is constructed from scratch, the algorithm
requires time where is the sum of the lengths
of other common substrings of and . When the suffix tree of is
already given, it requires time.Comment: 12 page
The Russian Mission: Seventh-Day Adventism, Bolshevism, and the Imminent Apocalypse, 1881 - 1946
The first Adventist missionaries made their way into Russia in the late 1880’s, where they experienced imprisonment, exile, and sometimes both. The scope of my thesis concerns the Seventh-Day Adventist Church and how Adventist missionaries and leaders endeavored on the Russian Mission. Using the writings, letters, and correspondence of these missionaries, as well as the myriad Adventist periodicals, I explain and analyze the evolution of the Mission from its inception to the end of the Second World War. In what ways did Adventist missionaries or Adventist media outlets abroad understand, explain, or justify the Russian Mission and its hardships? What characterized the Russian Mission through this transitional period? How can we understand the Russian Mission, through the Seventh-Day Adventist Church’s own writings and words, during the imperial period, the revolutionary period, and the early Soviet period? Why, in 1928, did Adventist periodicals stop calling for more evangelical missions and start heralding the second advent of Christ? What is the cause and significance of apocalyptic rhetoric?
The missionaries, proselytizing in Russia during the imperial era, only ever discussed the prophetic potential of the Russian Mission; Adventist periodicals mirrored these sentiments, despite circulating stories of persecution at the hands of the Russian Orthodox Church and the autocracy. Russia’s entrance into the Great War, the consequent Russian Revolutions and Civil War, and the subsequent Volga Famine created an era of uncertainty for the Russian Mission, lasting well into the 1920’s; again, Adventists in Russia and abroad heralded the Mission as an apostolic success. Beginning in 1924, these feelings of hope began to fade, as missionary groups on the ground lost contact and communication with domestic Adventist centers. Instead of the hope-filled calls to Russia, however, outlets of the Adventist media began developing an understanding of the coming apocalypse. By 1928, the activities and goals of the Russian Mission had disappeared, and Adventists came to see Russia as the staging ground for an imminent and personal second advent of Christ
Tree-chromatic number is not equal to path-chromatic number
For a graph and a tree-decomposition of , the
chromatic number of is the maximum of , taken
over all bags . The tree-chromatic number of is the
minimum chromatic number of all tree-decompositions of .
The path-chromatic number of is defined analogously. In this paper, we
introduce an operation that always increases the path-chromatic number of a
graph. As an easy corollary of our construction, we obtain an infinite family
of graphs whose path-chromatic number and tree-chromatic number are different.
This settles a question of Seymour. Our results also imply that the
path-chromatic numbers of the Mycielski graphs are unbounded.Comment: 11 pages, 0 figure
The factorizable amplitude in
Using the measured spectrum shape for , the rate for , information on the Cabibbo-Kobayashi-Maskawa (CKM) matrix
element , and theoretical inputs from factorization and lattice gauge
theory, we obtain an improved estimate of the ``tree'' contribution to . We find the branching ratio \b(B^0 \to \pi^+ \pi^-)|_{\rm tree}
= (5.25^{+1.67}_{-0.50}) \times 10^{-6}, to be compared with the experimental
value \b(B^0 \to \pi^+ \pi^-) = (4.55 \pm 0.44) \times 10^{-6}. The fit
implies . Implications for
tree-penguin interference in and for other charmless
decays are discussed.Comment: 11 pages, LaTeX, 3 figures, to be submitted to Phys. Rev.
Isotropic Dynamic Hierarchical Clustering
We face a need of discovering a pattern in locations of a great number of
points in a high-dimensional space. Goal is to group the close points together.
We are interested in a hierarchical structure, like a B-tree. B-Trees are
hierarchical, balanced, and they can be constructed dynamically. B-Tree
approach allows to determine the structure without any supervised learning or a
priori knowlwdge. The space is Euclidean and isotropic. Unfortunately, there
are no B-Tree implementations processing indices in a symmetrical and
isotropical way. Some implementations are based on constructing compound
asymmetrical indices from point coordinates; and the others split the nodes
along the coordinate hyper-planes. We need to process tens of millions of
points in a thousand-dimensional space. The application has to be scalable.
Ideally, a cluster should be an ellipsoid, but it would require to store O(n2)
ellipse axes. So, we are using multi-dimensional balls defined by the centers
and radii. Calculation of statistical values like the mean and the average
deviation, can be done in an incremental way. While adding a point to a tree,
the statistical values for nodes recalculated in O(1) time. We support both,
brute force O(2n) and greedy O(n2) split algorithms. Statistical and aggregated
node information also allows to manipulate (to search, to delete) aggregated
sets of closely located points. Hierarchical information retrieval. When
searching, the user is provided with the highest appropriate nodes in the tree
hierarchy, with the most important clusters emerging in the hierarchy
automatically. Then, if interested, the user may navigate down the tree to more
specific points. The system is implemented as a library of Java classes
representing Points, Sets of points with aggregated statistical information,
B-tree, and Nodes with a support of serialization and storage in a MySQL
database.Comment: 6 pages with 3 example
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