author | Dominic Pinkman <Dominic.Pinkman@Nokia.com> |
Thu, 21 Jan 2010 18:18:20 +0000 | |
changeset 0 | 89d6a7a84779 |
permissions | -rw-r--r-- |
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89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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<?xml version="1.0" encoding="utf-8"?> |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. --> |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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<!-- This component and the accompanying materials are made available under the terms of the License |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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"Eclipse Public License v1.0" which accompanies this distribution, |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". --> |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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<!-- Initial Contributors: |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
parents:
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Nokia Corporation - initial contribution. |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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Contributors: |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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--> |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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<!DOCTYPE concept |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd"> |
89d6a7a84779
Initial contribution of Documentation_content according to Feature bug 1266 bug 1268 bug 1269 bug 1270 bug 1372 bug 1374 bug 1375 bug 1379 bug 1380 bug 1381 bug 1382 bug 1383 bug 1385
Dominic Pinkman <Dominic.Pinkman@Nokia.com>
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<concept xml:lang="en" id="GUID-785B2F0B-E7E6-5DAE-98F1-6C32BED25964"><title>Database storage overhead</title><prolog><metadata><keywords/></metadata></prolog><conbody><p>Space utilization is efficient</p> <ul><li id="GUID-8AE05C00-0C7E-5D9C-AC2B-DC1D5432DF0D"><p>the underlying permanent file store adds minimal overhead to maintain its structure: store imposes a fixed 46 bytes + 2 bytes per additional 16K; each stream requires 7 bytes.</p> </li> <li id="GUID-5BDB30B0-9140-55AA-A7BE-4C4B30355ADE"><p>the database has minimal space requirements to store its schema and data structure.</p> </li> <li id="GUID-3FCF5F99-767F-5526-B0AF-40F7F248CF26"><p>including the stream overhead, row storage overhead can be less than 2 bytes per row in ideal clustering conditions, even with lower clustering the overhead is usually below 1% of the data volume.</p> </li> </ul> <p>The storage required for a row can be determined as follows:</p> <ul><li id="GUID-41E7E40C-6E34-5C7A-BB82-A0AF92B5D455"><p>each non-null value requires the storage for fixed width columns, and the raw storage plus 1 byte for variable width columns.</p> </li> <li id="GUID-845C1A45-8C1F-5EA0-A3A6-787359332505"><p>long columns are stored embedded in the row data when they are small enough, and otherwise they are stored in a separate stream: this makes more efficient use of the both space and speed. When embedded they require just 1 bit more than the short columns, when separated they require 8 bytes in the row data plus any stream overhead.</p> </li> <li id="GUID-CD64205E-894B-50D3-9AAA-ACA375D820EA"><p>each nullable column requires an extra 1 bit.</p> </li> <li id="GUID-4FF233BB-3863-5869-9E6E-E56AC3B29924"><p>bits are packed into bytes in the row storage.</p> </li> </ul> <section><title>Indexes</title> <p>Indexes are implemented using STORE B+trees. Note in particular that indexes use fixed length keys, so that indexes on longer text fields can consume significant space.</p> <p>If the key for the index is <i>k</i> bytes, the number of rows to index is <i>n</i>, the index page size is <i>P</i>, and the B-tree packing density is <i>r</i>:</p> <p><i>a = [(P-8)/(k+4)] * r</i> </p> <p>Where <i>[x]</i> is the largest integer <= <i>x</i>. Then the number of pages required, <i>N</i>, is</p> <p><i>N = n * (1/a + 1/(a*a))</i> </p> <p>Each page requires <i>P+7</i> bytes in the store, so the total indexing overhead, <i>S</i>, is</p> <p><i>S = N * (P+7)</i> </p> <p>For DBMS <i>P=512</i> and <i>r=0.86</i>.</p> </section> </conbody></concept> |