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Overview
Comment: | Fix off-by-one errors in the header comments of btree.c. Ticket #2272. (CVS 3726) |
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Downloads: | Tarball | ZIP archive |
Timelines: | family | ancestors | descendants | both | trunk |
Files: | files | file ages | folders |
SHA1: |
a70ea7202d8ffb0321ff8f2e5036731b |
User & Date: | drh 2007-03-27 14:05:23.000 |
Context
2007-03-27
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14:44 | The -DSQLITE_OMIT_ATTACH=1 option now omits both the ATTACH and VACUUM commands. Ticket #2268. The regression test suite depends on both of these commands and will not run if compiled with this option. (CVS 3727) (check-in: cbebfb8960 user: drh tags: trunk) | |
14:05 | Fix off-by-one errors in the header comments of btree.c. Ticket #2272. (CVS 3726) (check-in: a70ea7202d user: drh tags: trunk) | |
13:36 | More strict aliasing fixes. The single source file library now runs successfully with -fstrict-alias. (CVS 3725) (check-in: c8a8a189a8 user: drh tags: trunk) | |
Changes
Changes to src/btree.c.
1 2 3 4 5 6 7 8 9 10 11 | /* ** 2004 April 6 ** ** The author disclaims copyright to this source code. In place of ** a legal notice, here is a blessing: ** ** May you do good and not evil. ** May you find forgiveness for yourself and forgive others. ** May you share freely, never taking more than you give. ** ************************************************************************* | | | | | | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | /* ** 2004 April 6 ** ** The author disclaims copyright to this source code. In place of ** a legal notice, here is a blessing: ** ** May you do good and not evil. ** May you find forgiveness for yourself and forgive others. ** May you share freely, never taking more than you give. ** ************************************************************************* ** $Id: btree.c,v 1.343 2007/03/27 14:05:23 drh Exp $ ** ** This file implements a external (disk-based) database using BTrees. ** For a detailed discussion of BTrees, refer to ** ** Donald E. Knuth, THE ART OF COMPUTER PROGRAMMING, Volume 3: ** "Sorting And Searching", pages 473-480. Addison-Wesley ** Publishing Company, Reading, Massachusetts. ** ** The basic idea is that each page of the file contains N database ** entries and N+1 pointers to subpages. ** ** ---------------------------------------------------------------- ** | Ptr(0) | Key(0) | Ptr(1) | Key(1) | ... | Key(N-1) | Ptr(N) | ** ---------------------------------------------------------------- ** ** All of the keys on the page that Ptr(0) points to have values less ** than Key(0). All of the keys on page Ptr(1) and its subpages have ** values greater than Key(0) and less than Key(1). All of the keys ** on Ptr(N) and its subpages have values greater than Key(N-1). And ** so forth. ** ** Finding a particular key requires reading O(log(M)) pages from the ** disk where M is the number of entries in the tree. ** ** In this implementation, a single file can hold one or more separate ** BTrees. Each BTree is identified by the index of its root page. The ** key and data for any entry are combined to form the "payload". A ** fixed amount of payload can be carried directly on the database ** page. If the payload is larger than the preset amount then surplus ** bytes are stored on overflow pages. The payload for an entry ** and the preceding pointer are combined to form a "Cell". Each ** page has a small header which contains the Ptr(N) pointer and other ** information such as the size of key and data. ** ** FORMAT DETAILS ** ** The file is divided into pages. The first page is called page 1, ** the second is page 2, and so forth. A page number of zero indicates ** "no such page". The page size can be anything between 512 and 65536. |
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119 120 121 122 123 124 125 | ** ** OFFSET SIZE DESCRIPTION ** 0 1 Flags. 1: intkey, 2: zerodata, 4: leafdata, 8: leaf ** 1 2 byte offset to the first freeblock ** 3 2 number of cells on this page ** 5 2 first byte of the cell content area ** 7 1 number of fragmented free bytes | | | 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 | ** ** OFFSET SIZE DESCRIPTION ** 0 1 Flags. 1: intkey, 2: zerodata, 4: leafdata, 8: leaf ** 1 2 byte offset to the first freeblock ** 3 2 number of cells on this page ** 5 2 first byte of the cell content area ** 7 1 number of fragmented free bytes ** 8 4 Right child (the Ptr(N) value). Omitted on leaves. ** ** The flags define the format of this btree page. The leaf flag means that ** this page has no children. The zerodata flag means that this page carries ** only keys and no data. The intkey flag means that the key is a integer ** which is stored in the key size entry of the cell header rather than in ** the payload area. ** |
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