Improved comments on the OP_Column changes. Optimize out loading of overflow

pages for content with zero length.  Add test cases for the latter.

FossilOrigin-Name: 0e05679db7aa302a49e087a81f85203844b98cbe

manifest

@@ -1,5 +1,5 @@
-C Further\sperformance\stweaks\sto\sOP_Column.
+C Improved\scomments\son\sthe\sOP_Column\schanges.\s\sOptimize\sout\sloading\sof\soverflow\npages\sfor\scontent\swith\szero\slength.\s\sAdd\stest\scases\sfor\sthe\slatter.
-D 2013-11-20T19:28:03.982
+D 2013-11-20T20:58:00.360
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 8a07bebafbfda0eb67728f4bd15a36201662d1a1
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -280,7 +280,7 @@ F src/update.c c05a0ee658f1a149e0960dfd110f3b8bd846bcb0
 F src/utf.c 6fc6c88d50448c469c5c196acf21617a24f90269
 F src/util.c 2fa6c821d28bbdbeec1b2a7b091a281c9ef8f918
 F src/vacuum.c 3728d74919d4fb1356f9e9a13e27773db60b7179
-F src/vdbe.c 1a6e2c9413fca3b2d00c49e85a861e0adc8b6c6a
+F src/vdbe.c 987f375b8ba5b5c3d0ded64191f72706221f76f9
 F src/vdbe.h c06f0813f853566457ce9cfb1a4a4bc39a5da644
 F src/vdbeInt.h fbae1c449049a1a26ebbdf44e1beb08344072b72
 F src/vdbeapi.c 93a22a9ba2abe292d5c2cf304d7eb2e894dde0ed
@@ -573,7 +573,7 @@ F test/fts4merge4.test c19c85ca1faa7b6d536832b49c12e1867235f584
 F test/fts4noti.test aed33ba44808852dcb24bf70fa132e7bf530f057
 F test/fts4unicode.test e28ba1a14181e709dcdf47455f207adf14c7cfe0
 F test/full.test 6b3c8fb43c6beab6b95438c1675374b95fab245d
-F test/func.test c7e80a44eebac8604397eb2ad83d0d5d9d541237
+F test/func.test 00667bbeac044d007f6f021af1b9f6150f0c7ff8
 F test/func2.test 772d66227e4e6684b86053302e2d74a2500e1e0f
 F test/func3.test dbccee9133cfef1473c59ec07b5f0262b9d72f9a
 F test/func4.test 6beacdfcb0e18c358e6c2dcacf1b65d1fa80955f
@@ -1140,7 +1140,7 @@ F tool/vdbe-compress.tcl f12c884766bd14277f4fcedcae07078011717381
 F tool/warnings-clang.sh f6aa929dc20ef1f856af04a730772f59283631d4
 F tool/warnings.sh d1a6de74685f360ab718efda6265994b99bbea01
 F tool/win/sqlite.vsix 030f3eeaf2cb811a3692ab9c14d021a75ce41fff
-P 7c914e3997d2b28164a2fa7eb4398262b6ddb4b2
+P 0e3f5df695216a27602a53eed5d25231b055adc8
-R 72749b37eba95a49879e9308fdcd90bb
+R 7b4a6a3b4e08d369fabb1ea696a3ba02
 U drh
-Z 441207295dddfadd80f4cc85b77f0a53
+Z a02194f256e2495862011254263d6e91

manifest.uuid

@@ -1 +1 @@
-0e3f5df695216a27602a53eed5d25231b055adc8
+0e05679db7aa302a49e087a81f85203844b98cbe

src/vdbe.c

@@ -2284,11 +2284,11 @@ case OP_Column: {
   aType = pC->aType;
   aOffset = pC->aOffset;
 #ifndef SQLITE_OMIT_VIRTUALTABLE
-  assert( pC->pVtabCursor==0 );
+  assert( pC->pVtabCursor==0 ); /* OP_Column never called on virtual table */
 #endif
   pCrsr = pC->pCursor;
-  assert( pCrsr!=0 || pC->pseudoTableReg>0 );
+  assert( pCrsr!=0 || pC->pseudoTableReg>0 ); /* pCrsr NULL on PseudoTables */
-  assert( pC->pseudoTableReg==0 || pC->nullRow );
+  assert( pCrsr!=0 || pC->nullRow );          /* pC->nullRow on PseudoTables */
 
   /* If the cursor cache is stale, bring it up-to-date */
   rc = sqlite3VdbeCursorMoveto(pC);
@@ -2339,12 +2339,15 @@ case OP_Column: {
         goto too_big;
       }
     }
-      
     pC->cacheStatus = p->cacheCtr;
     pC->iHdrOffset = getVarint32(pC->aRow, offset);
     pC->nHdrParsed = 0;
     aOffset[0] = offset;
     if( avail<offset ){
+      /* pC->aRow does not have to hold the entire row, but it does at least
+      ** need to cover the header of the record.  If pC->aRow does not contain
+      ** the complete header, then set it to zero, forcing the header to be
+      ** dynamically allocated. */
       pC->aRow = 0;
       pC->szRow = 0;
     }
@@ -2368,8 +2371,8 @@ case OP_Column: {
   ** parsed and valid information is in aOffset[] and aType[].
   */
   if( pC->nHdrParsed<=p2 ){
-    /* If there is more header available for parsing, try to extract 
+    /* If there is more header available for parsing in the record, try
-    ** additional fields up through the p2-th field 
+    ** to extract additional fields up through the p2+1-th field 
     */
     if( pC->iHdrOffset<aOffset[0] ){
       /* Make sure zData points to enough of the record to cover the header. */
@@ -2430,9 +2433,10 @@ case OP_Column: {
       }
     }
 
-    /* If after nHdrParsed is still not up to p2, that means that the record
+    /* If after trying to extra new entries from the header, nHdrParsed is
-    ** has fewer than p2 columns.  So the result will be either the default
+    ** still not up to p2, that means that the record has fewer than p2
-    ** value or a NULL. */
+    ** columns.  So the result will be either the default value or a NULL.
+    */
     if( pC->nHdrParsed<=p2 ){
       if( pOp->p4type==P4_MEM ){
         sqlite3VdbeMemShallowCopy(pDest, pOp->p4.pMem, MEM_Static);
@@ -2443,33 +2447,33 @@ case OP_Column: {
     }
   }
 
-  /* Get the column information. If aOffset[p2] is non-zero, then 
+  /* Extract the content for the p2+1-th column.  Control can only
-  ** deserialize the value from the record. If aOffset[p2] is zero,
+  ** reach this point if aOffset[p2], aOffset[p2+1], and aType[p2] are
-  ** then there are not enough fields in the record to satisfy the
+  ** all valid.
-  ** request.  In this case, set the value NULL or to P4 if P4 is
-  ** a pointer to a Mem object.
   */
   assert( p2<pC->nHdrParsed );
   assert( rc==SQLITE_OK );
   if( pC->szRow>=aOffset[p2+1] ){
-    /* This is the common case where the whole row fits on a single page */
+    /* This is the common case where the desired content fits on the original
+    ** page - where the content is not on an overflow page */
     VdbeMemRelease(pDest);
     sqlite3VdbeSerialGet(pC->aRow+aOffset[p2], aType[p2], pDest);
   }else{
-    /* This branch happens only when the row overflows onto multiple pages */
+    /* This branch happens only when content is on overflow pages */	
     t = aType[p2];
-    if( (pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
+    if( ((pOp->p5 & (OPFLAG_LENGTHARG|OPFLAG_TYPEOFARG))!=0
-     && ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0)
+          && ((t>=12 && (t&1)==0) || (pOp->p5 & OPFLAG_TYPEOFARG)!=0))
+     || (len = sqlite3VdbeSerialTypeLen(t))==0
     ){
       /* Content is irrelevant for the typeof() function and for
       ** the length(X) function if X is a blob.  So we might as well use
       ** bogus content rather than reading content from disk.  NULL works
       ** for text and blob and whatever is in the payloadSize64 variable
-      ** will work for everything else. */
+      ** will work for everything else.  Content is also irrelevant if
-      zData = t<12 ? (u8*)&payloadSize64 : 0;
+      ** the content length is 0. */
+      zData = t<=13 ? (u8*)&payloadSize64 : 0;
       sMem.zMalloc = 0;
     }else{
-      len = sqlite3VdbeSerialTypeLen(t);
       memset(&sMem, 0, sizeof(sMem));
       sqlite3VdbeMemMove(&sMem, pDest);
       rc = sqlite3VdbeMemFromBtree(pCrsr, aOffset[p2], len,  pC->isIndex,

test/func.test

@@ -1319,6 +1319,24 @@ do_test func-29.6 {
   set x
 } {1}
 
+# The OP_Column opcode has an optimization that avoids loading content
+# for fields with content-length=0 when the content offset is on an overflow
+# page.  Make sure the optimization works.
+#
+do_execsql_test func-29.10 {
+  CREATE TABLE t29b(a,b,c,d,e,f,g,h,i);
+  INSERT INTO t29b 
+   VALUES(1, hex(randomblob(2000)), null, 0, 1, '', zeroblob(0),'x',x'01');
+  SELECT typeof(c), typeof(d), typeof(e), typeof(f),
+         typeof(g), typeof(h), typeof(i) FROM t29b;
+} {null integer integer text blob text blob}
+do_execsql_test func-29.11 {
+  SELECT length(f), length(g), length(h), length(i) FROM t29b;
+} {0 0 1 1}
+do_execsql_test func-29.12 {
+  SELECT quote(f), quote(g), quote(h), quote(i) FROM t29b;
+} {'' X'' 'x' X'01'}
+
 # EVIDENCE-OF: R-29701-50711 The unicode(X) function returns the numeric
 # unicode code point corresponding to the first character of the string
 # X.