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Overview
| Comment: | Update the compile-time options document and footprint size bounds. Updates to the file format document. |
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| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
0992cf9ad0f531dc3239bf521025fcc8 |
| User & Date: | drh 2010-07-07 02:03:16 |
Context
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2010-07-08
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| 18:12 | Update PRAGMA journal_mode documentation. Fix typos in the wal.html document. check-in: b1e171c029 user: drh tags: trunk | |
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2010-07-07
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| 02:03 | Update the compile-time options document and footprint size bounds. Updates to the file format document. check-in: 0992cf9ad0 user: drh tags: trunk | |
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2010-07-06
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| 01:27 | Adding first draft of WAL file format. check-in: 05824b6e6a user: drh tags: trunk | |
Changes
Changes to pages/compile.in.
575 575 that employ the BETWEEN operator. 576 576 } 577 577 578 578 COMPILE_OPTION {SQLITE_OMIT_BLOB_LITERAL} { 579 579 When this option is defined, it is not possible to specify a blob in 580 580 an SQL statement using the X'ABCD' syntax. 581 581 } 582 + 583 +COMPILE_OPTION {SQLITE_OMIT_BTREECOUNT} { 584 + When this option is defined, an optimization that accelerates counting 585 + all entires in a table (in other words, an optimization that helps 586 + "SELECT count(*) FROM table" run faster) is omitted. 587 +} 582 588 583 589 COMPILE_OPTION {SQLITE_OMIT_BUILTIN_TEST} { 584 590 A standard SQLite build includes a small amount of logic controlled 585 591 by the [sqlite3_test_control()] interface that is used to exercise 586 592 parts of the SQLite core that are difficult to control and measure using 587 593 the standard API. This option omits that built-in test logic. 588 594 } ................................................................................ 593 599 594 600 COMPILE_OPTION {SQLITE_OMIT_CHECK} { 595 601 This option causes SQLite to omit support for CHECK constraints. 596 602 The parser will still accept CHECK constraints in SQL statements, 597 603 they will just not be enforced. 598 604 } 599 605 600 -COMPILE_OPTION {SQLITE_OMIT_COMPLETE} { 601 - This option causes the [sqlite3_complete()] and [sqlite3_complete16()] 602 - interfaces to be omitted. 603 -} 604 - 605 606 COMPILE_OPTION {SQLITE_OMIT_COMPILEOPTION_DIAGS} { 606 607 This option is used to omit the compile-time option diagnostics available 607 608 in SQLite, including the [sqlite3_compileoption_used()] and 608 609 [sqlite3_compileoption_get()] C/C++ functions, the 609 610 [sqlite_compileoption_used()] and [sqlite_compileoption_get()] SQL functions, 610 611 and the [compile_options pragma]. 611 612 } 613 + 614 +COMPILE_OPTION {SQLITE_OMIT_COMPLETE} { 615 + This option causes the [sqlite3_complete()] and [sqlite3_complete16()] 616 + interfaces to be omitted. 617 +} 612 618 613 619 COMPILE_OPTION {SQLITE_OMIT_COMPOUND_SELECT} { 614 620 This option is used to omit the compound [SELECT] functionality. 615 621 [SELECT] statements that use the 616 622 UNION, UNION ALL, INTERSECT or EXCEPT compound SELECT operators will 617 623 cause a parse error. 618 624 } ................................................................................ 644 650 [sqlite3_global_recover()], 645 651 [sqlite3_thread_cleanup()] and 646 652 [sqlite3_memory_alarm()] interfaces. 647 653 } 648 654 649 655 COMPILE_OPTION {SQLITE_OMIT_DISKIO} { 650 656 This option omits all support for writing to the disk and forces 651 - databases to exist in memory only. 657 + databases to exist in memory only. This option has not been 658 + maintained and probably does not work with newer versions of SQLite. 652 659 } 653 660 654 661 COMPILE_OPTION {SQLITE_OMIT_EXPLAIN} { 655 662 Defining this option causes the [EXPLAIN] command to be omitted from the 656 663 library. Attempting to execute an [EXPLAIN] statement will cause a parse 657 664 error. 658 665 } ................................................................................ 706 713 707 714 COMPILE_OPTION {SQLITE_OMIT_LOCALTIME} { 708 715 This option omits the "localtime" modifier from the date and time 709 716 functions. This option is sometimes useful when trying to compile 710 717 the date and time functions on a platform that does not support the 711 718 concept of local time. 712 719 } 720 + 721 +COMPILE_OPTION {SQLITE_OMIT_LOOKASIDE} { 722 + This option omits the [lookaside memory allocator]. 723 +} 713 724 714 725 COMPILE_OPTION {SQLITE_OMIT_MEMORYDB} { 715 726 When this is defined, the library does not respect the special database 716 727 name ":memory:" (normally used to create an [in-memory database]). If 717 728 ":memory:" is passed to [sqlite3_open()], [sqlite3_open16()], or 718 729 [sqlite3_open_v2()], a file with this name will be 719 730 opened or created. ................................................................................ 835 846 for which the schema contains VIEW objects. 836 847 } 837 848 838 849 COMPILE_OPTION {SQLITE_OMIT_VIRTUALTABLE} { 839 850 This option omits support for the [sqlite3_vtab | Virtual Table] 840 851 mechanism in SQLite. 841 852 } 853 + 854 +COMPILE_OPTION {SQLITE_OMIT_WAL} { 855 + This option omits the "[write-ahead log]" (a.k.a. "[WAL]") capability. 856 +} 842 857 843 858 COMPILE_OPTION {SQLITE_OMIT_WSD} { 844 859 This options builds a version of the SQLite library that contains no 845 860 Writable Static Data (WSD). WSD is global variables and/or static 846 861 variables. Some platforms do not support WSD, and this option is necessary 847 862 in order for SQLite to work those platforms. 848 863
Changes to pages/features.in.
12 12 (<a href="omitted.html">Features not supported</a>)</li> 13 13 <li>A complete database is stored in a 14 14 <a href="onefile.html">single cross-platform disk file</a>.</li> 15 15 <li>Supports terabyte-sized databases and gigabyte-sized strings 16 16 and blobs. (See <a href="limits.html">limits.html</a>.) 17 17 <li>Small code footprint: 18 18 <a href="http://www.sqlite.org/cvstrac/wiki?p=SizeOfSqlite"> 19 - less than 300KiB</a> fully configured or less 20 - than 180KiB with optional features omitted.</li> 19 + less than 325KiB</a> fully configured or less 20 + than 190KiB with optional features omitted.</li> 21 21 <li><a href="speed.html">Faster</a> than popular client/server database 22 22 engines for most common operations.</li> 23 23 <li>Simple, easy to use <a href="c3ref/intro.html">API</a>.</li> 24 24 <li>Written in ANSI-C. <a href="tclsqlite.html">TCL bindings</a> included. 25 25 Bindings for dozens of other languages 26 26 <a href="http://www.sqlite.org/cvstrac/wiki?p=SqliteWrappers"> 27 27 available separately.</a></li>
Changes to pages/fileformat2.in.
1255 1255 magic number in the first 4 bytes of the WAL header is 0x377f0683 and 1256 1256 the integers are little-endian the magic number is 0x377f0682. 1257 1257 The checksum values are always stored in the frame header in a 1258 1258 big-endian format regardless of which byte order is used to compute 1259 1259 the checksum.</p> 1260 1260 1261 1261 <p>The checksum algorithm only works for content which is a multiple of 1262 -8 bytes in length. In other words, if the puts are x(0) through x(N) 1262 +8 bytes in length. In other words, if the inputs are x(0) through x(N) 1263 1263 then N must be odd. 1264 1264 The checksum algorithm is as follows: 1265 1265 1266 1266 <blockquote><pre> 1267 1267 s0 = s1 = 0 1268 1268 for i from 0 to n-1 step 2: 1269 1269 s0 += x(i) + s1; ................................................................................ 1304 1304 frame or are followed by a commit frame, then page P is read from 1305 1305 the database file.</p> 1306 1306 1307 1307 <p>To start a read transaction, the reader records the index of the last 1308 1308 valid frame in the WAL. The reader uses this recorded "mxFrame" value 1309 1309 for all subsequent read operations. New transactions can be appended 1310 1310 to the WAL, but as long as the reader uses its original mxFrame value 1311 -and ignores the newly appended content, it will see a consistent snapshot 1312 -of the database from a single point in time. This technique allows 1313 -multiple concurrent readers to view different versions of the database 1314 -content simultaneously.</p> 1311 +and ignores subsequently appended content, the reader will see a 1312 +consistent snapshot of the database from a single point in time. 1313 +This technique allows multiple concurrent readers to view different 1314 +versions of the database content simultaneously.</p> 1315 1315 1316 1316 <p>The reader algorithm in the previous paragraphs works correctly, but 1317 1317 because frames for page P can appear anywhere within the WAL, the 1318 1318 reader has to scan the entire WAL looking for page P frames. If the 1319 1319 WAL is large (multiple megabytes is typical) that scan can be slow, 1320 1320 and read performance suffers. To overcome this problem, a separate 1321 1321 data structure called the wal-index is maintained to expedite the 1322 1322 search for frames of a particular page.</p> 1323 1323 1324 1324 <tcl>hd_fragment walindexformat {WAL-index format}</tcl> 1325 1325 <h3>4.5 WAL-Index Format</h3> 1326 1326 1327 1327 <p>Conceptually, the wal-index is shared memory, though the current 1328 -VFS implementations use a mmapped file for the wal-index. Because 1328 +VFS implementations use a mmapped file for the wal-index. The mmapped 1329 +file is in the same directory as the database and has the same name 1330 +as the database with a "<tt>-shm</tt>" suffix appended. Because 1329 1331 the wal-index is shared memory, SQLite does not support 1330 1332 [PRAGMA journal_mode | journal_mode=WAL] 1331 1333 on a network filesystem when clients are on different machines. 1332 1334 All users of the database must be able to share the same memory.</p> 1333 1335 1334 1336 <p>The purpose of the wal-index is to answer this question quickly:</p> 1335 1337 1336 1338 <blockquote><i> 1337 1339 Given a page number P and a maximum WAL frame index M, 1338 1340 return the largest WAL frame index for page P that does not exceed M, 1339 1341 or return NULL if there are no frames for page P that do not exceed M. 1340 1342 </i></blockquote> 1341 1343 1344 +<p>The <i>M</i> value in the previous paragraph is the "mxFrame" value 1345 +defined in [WAL read algorithm | section 4.4] that is read at the start 1346 +of a transaction and which defines the maximum frame from the WAL that 1347 +the reader will use.</p> 1342 1348 1343 1349 <p>The wal-index is transient. After a crash, the wal-index is 1344 1350 reconstructed from the original WAL file. The VFS is required 1345 1351 to either truncate or zero the header of the wal-index when the last 1346 1352 connection to it closes. Because the wal-index is transient, it can 1347 1353 use an architecture-specific format; it does not have to be cross-platform. 1348 1354 Hence, unlike the database and WAL file formats which store all values