Avoid preparing a SELECT statement each time an UPDATE or DELETE

by docid is executed against an fts3 table.

FossilOrigin-Name: 9962c10a5c6672bd82b2bf640d878fcdac0b815a

ext/fts3/fts3.c

@@ -492,6 +492,7 @@ static int fts3DisconnectMethod(sqlite3_vtab *pVtab){
   assert( p->pSegments==0 );
 
   /* Free any prepared statements held */
+  sqlite3_finalize(p->pSeekStmt);
   for(i=0; i<SizeofArray(p->aStmt); i++){
     sqlite3_finalize(p->aStmt[i]);
   }
@@ -1680,6 +1681,26 @@ static int fts3OpenMethod(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCsr){
   return SQLITE_OK;
 }
 
+/*
+** Finalize the statement handle at pCsr->pStmt.
+**
+** Or, if that statement handle is one created by fts3CursorSeekStmt(),
+** and the Fts3Table.pSeekStmt slot is currently NULL, save the statement
+** pointer there instead of finalizing it.
+*/
+static void fts3CursorFinalizeStmt(Fts3Cursor *pCsr){
+  if( pCsr->bSeekStmt ){
+    Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
+    if( p->pSeekStmt==0 ){
+      p->pSeekStmt = pCsr->pStmt;
+      sqlite3_reset(pCsr->pStmt);
+      pCsr->pStmt = 0;
+    }
+    pCsr->bSeekStmt = 0;
+  }
+  sqlite3_finalize(pCsr->pStmt);
+}
+
 /*
 ** Close the cursor.  For additional information see the documentation
 ** on the xClose method of the virtual table interface.
@@ -1687,7 +1708,7 @@ static int fts3OpenMethod(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **ppCsr){
 static int fts3CloseMethod(sqlite3_vtab_cursor *pCursor){
   Fts3Cursor *pCsr = (Fts3Cursor *)pCursor;
   assert( ((Fts3Table *)pCsr->base.pVtab)->pSegments==0 );
-  sqlite3_finalize(pCsr->pStmt);
+  fts3CursorFinalizeStmt(pCsr);
   sqlite3Fts3ExprFree(pCsr->pExpr);
   sqlite3Fts3FreeDeferredTokens(pCsr);
   sqlite3_free(pCsr->aDoclist);
@@ -1705,20 +1726,23 @@ static int fts3CloseMethod(sqlite3_vtab_cursor *pCursor){
 **
 ** (or the equivalent for a content=xxx table) and set pCsr->pStmt to
 ** it. If an error occurs, return an SQLite error code.
-**
-** Otherwise, set *ppStmt to point to pCsr->pStmt and return SQLITE_OK.
 */
-static int fts3CursorSeekStmt(Fts3Cursor *pCsr, sqlite3_stmt **ppStmt){
+static int fts3CursorSeekStmt(Fts3Cursor *pCsr){
   int rc = SQLITE_OK;
   if( pCsr->pStmt==0 ){
     Fts3Table *p = (Fts3Table *)pCsr->base.pVtab;
     char *zSql;
-    zSql = sqlite3_mprintf("SELECT %s WHERE rowid = ?", p->zReadExprlist);
-    if( !zSql ) return SQLITE_NOMEM;
-    rc = sqlite3_prepare_v2(p->db, zSql, -1, &pCsr->pStmt, 0);
-    sqlite3_free(zSql);
+    if( p->pSeekStmt ){
+      pCsr->pStmt = p->pSeekStmt;
+      p->pSeekStmt = 0;
+    }else{
+      zSql = sqlite3_mprintf("SELECT %s WHERE rowid = ?", p->zReadExprlist);
+      if( !zSql ) return SQLITE_NOMEM;
+      rc = sqlite3_prepare_v2(p->db, zSql, -1, &pCsr->pStmt, 0);
+      sqlite3_free(zSql);
+    }
+    if( rc==SQLITE_OK ) pCsr->bSeekStmt = 1;
   }
-  *ppStmt = pCsr->pStmt;
   return rc;
 }
 
@@ -1730,9 +1754,7 @@ static int fts3CursorSeekStmt(Fts3Cursor *pCsr, sqlite3_stmt **ppStmt){
 static int fts3CursorSeek(sqlite3_context *pContext, Fts3Cursor *pCsr){
   int rc = SQLITE_OK;
   if( pCsr->isRequireSeek ){
-    sqlite3_stmt *pStmt = 0;
-
-    rc = fts3CursorSeekStmt(pCsr, &pStmt);
+    rc = fts3CursorSeekStmt(pCsr);
     if( rc==SQLITE_OK ){
       sqlite3_bind_int64(pCsr->pStmt, 1, pCsr->iPrevId);
       pCsr->isRequireSeek = 0;
@@ -3190,7 +3212,7 @@ static int fts3FilterMethod(
   assert( iIdx==nVal );
 
   /* In case the cursor has been used before, clear it now. */
-  sqlite3_finalize(pCsr->pStmt);
+  fts3CursorFinalizeStmt(pCsr);
   sqlite3_free(pCsr->aDoclist);
   sqlite3Fts3MIBufferFree(pCsr->pMIBuffer);
   sqlite3Fts3ExprFree(pCsr->pExpr);
@@ -3258,7 +3280,7 @@ static int fts3FilterMethod(
       rc = SQLITE_NOMEM;
     }
   }else if( eSearch==FTS3_DOCID_SEARCH ){
-    rc = fts3CursorSeekStmt(pCsr, &pCsr->pStmt);
+    rc = fts3CursorSeekStmt(pCsr);
     if( rc==SQLITE_OK ){
       rc = sqlite3_bind_value(pCsr->pStmt, 1, pCons);
     }

ext/fts3/fts3Int.h

@@ -230,6 +230,7 @@ struct Fts3Table {
   ** statements is run and reset within a single virtual table API call. 
   */
   sqlite3_stmt *aStmt[40];
+  sqlite3_stmt *pSeekStmt;        /* Cache for fts3CursorSeekStmt() */
 
   char *zReadExprlist;
   char *zWriteExprlist;
@@ -299,6 +300,7 @@ struct Fts3Cursor {
   i16 eSearch;                    /* Search strategy (see below) */
   u8 isEof;                       /* True if at End Of Results */
   u8 isRequireSeek;               /* True if must seek pStmt to %_content row */
+  u8 bSeekStmt;                   /* True if pStmt is a seek */
   sqlite3_stmt *pStmt;            /* Prepared statement in use by the cursor */
   Fts3Expr *pExpr;                /* Parsed MATCH query string */
   int iLangid;                    /* Language being queried for */