SQLite4  Check-in [0b68007d89]

#include "btInt.h"

struct bt_db {
  sqlite4_env *pEnv;              /* SQLite environment */
  BtPager *pPager;                /* Underlying page-based database */
};

struct bt_cursor {
  bt_db *pDb;                     /* Database that owns this cursor */

  int nPg;                        /* Number of valid entries in apPage[] */
  int iCell;                      /* Current cell in apPage[nPg] */
  BtPage *apPage[32];             /* All pages from root to current leaf */
};

/*
** Allocate a new database handle.
*/
int sqlite4BtNew(sqlite4_env *pEnv, int nExtra, bt_db **ppDb){
  bt_db *db = 0;                  /* New database object */
  BtPager *pPager = 0;            /* Pager object for this database */
  int nReq;                       /* Bytes of space required for bt_db object */
  int rc;                         /* Return code */

  nReq = sizeof(bt_db);
  rc = sqlite4BtPagerNew(pEnv, nExtra + nReq, &pPager);
  if( rc==SQLITE4_OK ){
    db = (bt_db*)sqlite4BtPagerExtra(pPager);
    db->pPager = pPager;
    db->pEnv = pEnv;
  }

  *ppDb = db;
  return rc;
}

/*
** Close an existing database handle. Once this function has been 
** called, the handle may not be used for any purpose.
*/
int sqlite4BtClose(bt_db *db){
  if( db ){
    sqlite4BtPagerClose(db->pPager);
  }
  return SQLITE4_OK;
}

/*
** Return a pointer to the nExtra bytes of space allocated along with 
** the database handle. 
*/
void *sqlite4BtExtra(bt_db *db){
  return (void*)&db[1];
}

int sqlite4BtOpen(bt_db *db, const char *zFilename){
  int rc;
  rc = sqlite4BtPagerOpen(db->pPager, zFilename);
  return rc;
}

int sqlite4BtBegin(bt_db *db, int iLevel){
  int rc;
  rc = sqlite4BtPagerBegin(db->pPager, iLevel);
  return rc;
}

int sqlite4BtCommit(bt_db *db, int iLevel){
  int rc;
  rc = sqlite4BtPagerCommit(db->pPager, iLevel);
  return rc;
}

int sqlite4BtRevert(bt_db *db, int iLevel){
  int rc;
  rc = sqlite4BtPagerRevert(db->pPager, iLevel);
  return rc;
}

int sqlite4BtRollback(bt_db *db, int iLevel){
  int rc;
  rc = sqlite4BtPagerRollback(db->pPager, iLevel);
  return rc;
}

int sqlite4BtTransactionLevel(bt_db *db){
  return sqlite4BtPagerTransactionLevel(db->pPager);
}

int sqlite4BtCsrOpen(bt_db *db, int nExtra, bt_cursor **ppCsr){
  int rc;                         /* Return Code */
  int nByte;                      /* Total bytes of space to allocate */
  bt_cursor *pCsr;                /* New cursor object */

  nByte = sizeof(bt_cursor) + nExtra;
  pCsr = (bt_cursor*)sqlite4_malloc(db->pEnv, nByte);
  if( pCsr==0 ){
    rc = SQLITE4_NOMEM;
  }else{
    memset(pCsr, 0, nByte);
    pCsr->pDb = db;
  }

  return rc;
}

int sqlite4BtCsrClose(bt_cursor *pCsr){
  return SQLITE4_OK;
}

void *sqlite4BtCsrExtra(bt_cursor *pCsr){
  return (void*)&pCsr[1];
}

int sqlite4BtCsrSeek(bt_cursor *pCsr, const void *pK, int nK, int eSeek){
  return SQLITE4_OK;
}

static void btCsrReset(bt_cursor *pCsr){
  int i;
  for(i=0; i<pCsr->nPg; i++){
    sqlite4BtPageRelease(pCsr->apPage[i]);
  }
  pCsr->nPg = 0;
  pCsr->iCell = 0;
}

/*
** Position cursor pCsr to point to the smallest key in the database.
*/
int sqlite4BtCsrFirst(bt_cursor *pCsr){
  /* Reset the cursor */
  btCsrReset(pCsr);

  /* Load the root page into pCsr->apPage[0] */

  return SQLITE4_OK;
}

/*
** Position cursor pCsr to point to the largest key in the database.
*/
int sqlite4BtCsrLast(bt_cursor *pCsr){
  return SQLITE4_OK;
}

int sqlite4BtCsrNext(bt_cursor *pCsr){
  return SQLITE4_OK;
}

}

int sqlite4BtDelete(bt_cursor *pCsr){
  return SQLITE4_OK;
}

int sqlite4BtSetCookie(bt_db *db, unsigned int iVal){
  return sqlite4BtPagerSetCookie(db->pPager, iVal);
}

int sqlite4BtGetCookie(bt_db *db, unsigned int *piVal){
  return sqlite4BtPagerGetCookie(db->pPager, piVal);
}

<title>BT Design Overview</title>
<nowiki>

















<div id=start_of_toc></div>

&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#changes_to_locking style=text-decoration:none>2.1.3. Changes to Locking</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#read-only_clients_and_halted_databases style=text-decoration:none>2.1.3.5. Read-only Clients and Halted Databases</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#read-only_clients_and_live_databases style=text-decoration:none>2.1.3.6. Read-only Clients and Live Databases</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#b-tree_level_changes style=text-decoration:none>2.2. B-Tree Level Changes</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#free_page_management style=text-decoration:none>2.2.1. Free Page Management</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#large_records style=text-decoration:none>2.2.2. Large Records</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#b-tree_page_format style=text-decoration:none>2.2.3. B-Tree Page Format</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#page_formats style=text-decoration:none>2.2.3.7. Page Formats</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#cell_formats style=text-decoration:none>2.2.3.8. Cell Formats</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#merge-tree_database_notes style=text-decoration:none>3. Merge-Tree Database Notes</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#merge-tree_format style=text-decoration:none>3.1. Merge-Tree Format</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#in-memory_tree style=text-decoration:none>3.2. In-Memory Tree</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#use_of_a_background_thread_or_process style=text-decoration:none>3.3. Use of a Background Thread or Process</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#design_summary style=text-decoration:none>4. Design Summary</a><br>
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<a href=#locking style=text-decoration:none>4.1. Locking</a><br>

<ul>
  <li><p> Make it easy to avoid overreads.
  <li><p> Make binary searches as fast as possible.
</ul>

<p>
  Each b-tree page has a fixed-size header and a variable-sized footer. The
  purpose of moving some header data to a footer is to prevent buffer overreads
  occuring while attempting to read varint fields from the body of a corrupt
  b-tree page.

<h4 id=page_formats>2.2.3.7. Page Formats</h4>

<p><b>Page Header</b>

<p>Page headers are similar to those in SQLite3: 

<ul>
  <li> 1 byte - flags.
  <li> 2 bytes - Number of cells on this page.
  <li> 2 bytes - Offset of first byte after last cell.
  <li> Internal nodes only: 4 bytes - Page number of rightmost child node.
</ul>

<p><b>Page Footer</b>


<h4 id=cell_formats>2.2.3.8. Cell Formats</h4>

<p><b>B-Tree Nodes</b>

<p>Cell format:

<ul>
  <li> Number of bytes in the key-prefix (nKey), as a varint. Or, if the key-prefix for

  The pager level provides two sizes of allocation:
  <ul>
    <li> Page size (1-4 KB), and
    <li> Block size (512KB to 2MB).
  </ul>
</p>
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