[sql] SQLite patch to implement "smart" auto-vacuum.

third_party/sqlite/amalgamation/sqlite3.c

Index: third_party/sqlite/amalgamation/sqlite3.c
diff --git a/third_party/sqlite/amalgamation/sqlite3.c b/third_party/sqlite/amalgamation/sqlite3.c
index b849c15d32fe634b15faae851d4d518cdc395166..db273b2b4f395133a09b8b97d0f6d29e12debaf2 100644
--- a/third_party/sqlite/amalgamation/sqlite3.c
+++ b/third_party/sqlite/amalgamation/sqlite3.c
@@ -12266,6 +12266,8 @@ SQLITE_PRIVATE int sqlite3BtreeGetOptimalReserve(Btree*);
 SQLITE_PRIVATE int sqlite3BtreeGetReserveNoMutex(Btree *p);
 SQLITE_PRIVATE int sqlite3BtreeSetAutoVacuum(Btree *, int);
 SQLITE_PRIVATE int sqlite3BtreeGetAutoVacuum(Btree *);
+SQLITE_PRIVATE int sqlite3BtreeSetAutoVacuumSlackPages(Btree *, int);
+SQLITE_PRIVATE int sqlite3BtreeGetAutoVacuumSlackPages(Btree *);
 SQLITE_PRIVATE int sqlite3BtreeBeginTrans(Btree*,int);
 SQLITE_PRIVATE int sqlite3BtreeCommitPhaseOne(Btree*, const char *zMaster);
 SQLITE_PRIVATE int sqlite3BtreeCommitPhaseTwo(Btree*, int);
@@ -58368,6 +58370,7 @@ struct BtShared {
   u8 openFlags;         /* Flags to sqlite3BtreeOpen() */
 #ifndef SQLITE_OMIT_AUTOVACUUM
   u8 autoVacuum;        /* True if auto-vacuum is enabled */
+  u8 autoVacuumSlack;   /* Optional pages of slack for auto-vacuum */
   u8 incrVacuum;        /* True if incr-vacuum is enabled */
   u8 bDoTruncate;       /* True to truncate db on commit */
 #endif
@@ -61765,6 +61768,46 @@ SQLITE_PRIVATE int sqlite3BtreeGetAutoVacuum(Btree *p){
 #endif
 }
 
+/*
+** Change the 'auto-vacuum-slack-pages' property of the database. If auto vacuum
+** is enabled, this is the number of chunks of slack to allow before
+** automatically running an incremental vacuum.
+*/
+SQLITE_PRIVATE int sqlite3BtreeSetAutoVacuumSlackPages(Btree *p, int autoVacuumSlack){
+#ifdef SQLITE_OMIT_AUTOVACUUM
+  return SQLITE_READONLY;
+#else
+  BtShared *pBt = p->pBt;
+  int rc = SQLITE_OK;
+  u8 avs = (u8)autoVacuumSlack;
+  if( autoVacuumSlack>avs ){
+    avs = 0xFF;
+  }
+
+  sqlite3BtreeEnter(p);
+  pBt->autoVacuumSlack = avs;
+  sqlite3BtreeLeave(p);
+  return rc;
+#endif
+}
+
+/*
+** Return the value of the 'auto-vacuum-slack-pages' property.
+*/
+SQLITE_PRIVATE int sqlite3BtreeGetAutoVacuumSlackPages(Btree *p){
+#ifdef SQLITE_OMIT_AUTOVACUUM
+  return 0;
+#else
+  int rc = 0;
+  sqlite3BtreeEnter(p);
+  if( p->pBt->autoVacuum!=0 ){
+    rc = p->pBt->autoVacuumSlack;
+  }
+  sqlite3BtreeLeave(p);
+  return rc;
+#endif
+}
+
 
 /*
 ** Get a reference to pPage1 of the database file.  This will
@@ -62606,13 +62649,27 @@ SQLITE_PRIVATE int sqlite3BtreeIncrVacuum(Btree *p){
 */
 static int autoVacuumCommit(BtShared *pBt){
   int rc = SQLITE_OK;
+  int bShouldVacuum = pBt->autoVacuum && !pBt->incrVacuum;
   Pager *pPager = pBt->pPager;
   VVA_ONLY( int nRef = sqlite3PagerRefcount(pPager); )
 
   assert( sqlite3_mutex_held(pBt->mutex) );
   invalidateAllOverflowCache(pBt);
   assert(pBt->autoVacuum);
-  if( !pBt->incrVacuum ){
+  if( bShouldVacuum && pBt->autoVacuumSlack ){
+    Pgno nOrig;        /* Database size before freeing */
+    Pgno nFree;        /* Number of pages on the freelist initially */
+
+    nOrig = btreePagecount(pBt);
+    nFree = get4byte(&pBt->pPage1->aData[36]);
+    bShouldVacuum =
+        (nOrig-nFree-1)/pBt->autoVacuumSlack < (nOrig-1)/pBt->autoVacuumSlack;
+    /* TODO: When integrating this test with the following code, contrive to
+    ** trim to the integral chunk boundary, rather than trimming the entire free
+    ** list.
+    */
+  }
+  if( bShouldVacuum ){
     Pgno nFin;         /* Number of pages in database after autovacuuming */
     Pgno nFree;        /* Number of pages on the freelist initially */
     Pgno iFree;        /* The next page to be freed */
@@ -112205,6 +112262,7 @@ SQLITE_PRIVATE void sqlite3AutoLoadExtensions(sqlite3 *db){
 #define PragTyp_REKEY                         40
 #define PragTyp_LOCK_STATUS                   41
 #define PragTyp_PARSER_TRACE                  42
+#define PragTyp_AUTO_VACUUM_SLACK_PAGES       43
 
 /* Property flags associated with various pragma. */
 #define PragFlg_NeedSchema 0x01 /* Force schema load before running */
@@ -112302,6 +112360,13 @@ static const PragmaName aPragmaName[] = {
   /* ColNames:  */ 0, 0,
   /* iArg:      */ 0 },
 #endif
+#if !defined(SQLITE_OMIT_AUTOVACUUM)
+  { /* zName:     */ "auto_vacuum_slack_pages",
+    /* ePragTyp:  */ PragTyp_AUTO_VACUUM_SLACK_PAGES,
+    /* ePragFlg:  */ PragFlg_NeedSchema|PragFlg_Result0|PragFlg_SchemaReq|PragFlg_NoColumns1,
+    /* ColNames:  */ 0, 0,
+    /* iArg:      */ 0 },
+#endif
 #if !defined(SQLITE_OMIT_FLAG_PRAGMAS)
 #if !defined(SQLITE_OMIT_AUTOMATIC_INDEX)
  {/* zName:     */ "automatic_index",
@@ -113472,6 +113537,27 @@ SQLITE_PRIVATE void sqlite3Pragma(
   }
 #endif
 
+  /*
+  **  PRAGMA [schema.]auto_vacuum_slack_pages(N)
+  **
+  ** Control chunk size of auto-vacuum.
+  */
+#ifndef SQLITE_OMIT_AUTOVACUUM
+  case PragTyp_AUTO_VACUUM_SLACK_PAGES: {
+    Btree *pBt = pDb->pBt;
+    assert( pBt!=0 );
+    if( !zRight ){
+      returnSingleInt(v, sqlite3BtreeGetAutoVacuumSlackPages(pBt));
+    }else{
+      int nPages = 8;
+      if( sqlite3GetInt32(zRight, &nPages) ){
+        sqlite3BtreeSetAutoVacuumSlackPages(pBt, nPages);
+      }
+    }
+    break;
+  }
+#endif
+
 #ifndef SQLITE_OMIT_PAGER_PRAGMAS
   /*
   **  PRAGMA [schema.]cache_size