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SQLite training in Houston TX on 2019-11-05 (details)
Part of the 2019 Tcl Conference

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Overview
Comment:Improvements to the SQLITE_CONFIG_PAGECACHE documentation. Enhance the command-line shell to be able to take advantage of the full range of SQLITE_CONFIG_PAGECACHE capabilities, such as setting pMem==NULL and N<0.
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SHA1: 2518d5c971c4b32d9227b3bb7259162e3e27b00b
User & Date: drh 2015-11-11 15:28:52
Context
2015-11-12
14:57
First attempt at enhancing the "PRAGMA cache_spill" statement to accept a cache threashold size. check-in: 549d42be user: drh tags: cache_spill=N
2015-11-11
18:43
Fix missing word in a documentation comment. No changes to code. check-in: ed24d302 user: mistachkin tags: trunk
18:08
Add a hack to debug out a description of the WHERE clause of a SELECT (or other) statement. Use this in script tool/schemalint.tcl to automatically recommend indexes that might speed up specific queries. check-in: c6fa01c2 user: dan tags: schemalint
15:28
Improvements to the SQLITE_CONFIG_PAGECACHE documentation. Enhance the command-line shell to be able to take advantage of the full range of SQLITE_CONFIG_PAGECACHE capabilities, such as setting pMem==NULL and N<0. check-in: 2518d5c9 user: drh tags: trunk
2015-11-10
14:51
Improved output formatting for "PRAGMA parser_trace=ON;". check-in: e43e1171 user: drh tags: trunk
Changes
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Changes to src/shell.c.

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      if( n<1 ) n = 1;
      sqlite3_config(SQLITE_CONFIG_SCRATCH, malloc(n*sz+1), sz, n);
      data.shellFlgs |= SHFLG_Scratch;
    }else if( strcmp(z,"-pagecache")==0 ){
      int n, sz;
      sz = (int)integerValue(cmdline_option_value(argc,argv,++i));
      if( sz>70000 ) sz = 70000;
      if( sz<800 ) sz = 800;
      n = (int)integerValue(cmdline_option_value(argc,argv,++i));
      if( n<10 ) n = 10;
      sqlite3_config(SQLITE_CONFIG_PAGECACHE, malloc(n*sz+1), sz, n);

      data.shellFlgs |= SHFLG_Pagecache;
    }else if( strcmp(z,"-lookaside")==0 ){
      int n, sz;
      sz = (int)integerValue(cmdline_option_value(argc,argv,++i));
      if( sz<0 ) sz = 0;
      n = (int)integerValue(cmdline_option_value(argc,argv,++i));
      if( n<0 ) n = 0;







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      if( n<1 ) n = 1;
      sqlite3_config(SQLITE_CONFIG_SCRATCH, malloc(n*sz+1), sz, n);
      data.shellFlgs |= SHFLG_Scratch;
    }else if( strcmp(z,"-pagecache")==0 ){
      int n, sz;
      sz = (int)integerValue(cmdline_option_value(argc,argv,++i));
      if( sz>70000 ) sz = 70000;
      if( sz<0 ) sz = 0;
      n = (int)integerValue(cmdline_option_value(argc,argv,++i));

      sqlite3_config(SQLITE_CONFIG_PAGECACHE,
                    (n>0 && sz>0) ? malloc(n*sz) : 0, sz, n);
      data.shellFlgs |= SHFLG_Pagecache;
    }else if( strcmp(z,"-lookaside")==0 ){
      int n, sz;
      sz = (int)integerValue(cmdline_option_value(argc,argv,++i));
      if( sz<0 ) sz = 0;
      n = (int)integerValue(cmdline_option_value(argc,argv,++i));
      if( n<0 ) n = 0;

Changes to src/sqlite.h.in.

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** SQLITE_CONFIG_SCRATCH, SQLite avoids unnecessary large
** [sqlite3_malloc|heap allocations].
** This can help [Robson proof|prevent memory allocation failures] due to heap
** fragmentation in low-memory embedded systems.
** </dd>
**
** [[SQLITE_CONFIG_PAGECACHE]] <dt>SQLITE_CONFIG_PAGECACHE</dt>
** <dd> ^The SQLITE_CONFIG_PAGECACHE option specifies a static memory buffer
** that SQLite can use for the database page cache with the default page
** cache implementation.  
** This configuration should not be used if an application-define page
** cache implementation is loaded using the [SQLITE_CONFIG_PCACHE2]
** configuration option.
** ^There are three arguments to SQLITE_CONFIG_PAGECACHE: A pointer to
** 8-byte aligned
** memory, the size of each page buffer (sz), and the number of pages (N).

** The sz argument should be the size of the largest database page
** (a power of two between 512 and 65536) plus some extra bytes for each
** page header.  ^The number of extra bytes needed by the page header
** can be determined using the [SQLITE_CONFIG_PCACHE_HDRSZ] option 
** to [sqlite3_config()].
** ^It is harmless, apart from the wasted memory,
** for the sz parameter to be larger than necessary.  The first

** argument should pointer to an 8-byte aligned block of memory that
** is at least sz*N bytes of memory, otherwise subsequent behavior is
** undefined.
** ^SQLite will use the memory provided by the first argument to satisfy its
** memory needs for the first N pages that it adds to cache.  ^If additional





** page cache memory is needed beyond what is provided by this option, then
** SQLite goes to [sqlite3_malloc()] for the additional storage space.</dd>

**
** [[SQLITE_CONFIG_HEAP]] <dt>SQLITE_CONFIG_HEAP</dt>
** <dd> ^The SQLITE_CONFIG_HEAP option specifies a static memory buffer 
** that SQLite will use for all of its dynamic memory allocation needs
** beyond those provided for by [SQLITE_CONFIG_SCRATCH] and
** [SQLITE_CONFIG_PAGECACHE].
** ^The SQLITE_CONFIG_HEAP option is only available if SQLite is compiled







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** SQLITE_CONFIG_SCRATCH, SQLite avoids unnecessary large
** [sqlite3_malloc|heap allocations].
** This can help [Robson proof|prevent memory allocation failures] due to heap
** fragmentation in low-memory embedded systems.
** </dd>
**
** [[SQLITE_CONFIG_PAGECACHE]] <dt>SQLITE_CONFIG_PAGECACHE</dt>
** <dd> ^The SQLITE_CONFIG_PAGECACHE option a memory pool
** that SQLite can use for the database page cache with the default page
** cache implementation.  
** This configuration option is a no-op if an application-define page
** cache implementation is loaded using the [SQLITE_CONFIG_PCACHE2].

** ^There are three arguments to SQLITE_CONFIG_PAGECACHE: A pointer to
** 8-byte aligned memory (pMem), the size of each page cache line (sz),

** and the number of cache lines (N).
** The sz argument should be the size of the largest database page
** (a power of two between 512 and 65536) plus some extra bytes for each
** page header.  ^The number of extra bytes needed by the page header
** can be determined using [SQLITE_CONFIG_PCACHE_HDRSZ].

** ^It is harmless, apart from the wasted memory,
** for the sz parameter to be larger than necessary.  The pMem
** argument must be either a NULL pointer or a pointer to an 8-byte
** aligned block of memory of at least sz*N bytes, otherwise
** subsequent behavior is undefined.
** ^When pMem is not NULL, SQLite will strive to use the memory provided
** to satisfy page cache needs, falling back to [sqlite3_malloc()] if
** a page cache line is larger than sz bytes or if all of the pMem buffer
** is exhausted.
** ^If pMem is NULL and N is non-zero, then each database connection
** does an initial bulk allocation for page cache memory
** from [sqlite3_malloc()] sufficient for N cache lines if N is positive or
** of -1024*N bytes if N is negative, . ^If additional
** page cache memory is needed beyond what is provided by the initial
** allocation, then SQLite goes to [sqlite3_malloc()] separately for each
** additional cache line. </dd>
**
** [[SQLITE_CONFIG_HEAP]] <dt>SQLITE_CONFIG_HEAP</dt>
** <dd> ^The SQLITE_CONFIG_HEAP option specifies a static memory buffer 
** that SQLite will use for all of its dynamic memory allocation needs
** beyond those provided for by [SQLITE_CONFIG_SCRATCH] and
** [SQLITE_CONFIG_PAGECACHE].
** ^The SQLITE_CONFIG_HEAP option is only available if SQLite is compiled