Performance improvement in the OP_Column opcode.

FossilOrigin-Name: dc98a92f32511ee322b0207bd286e967248a8e59b418f11168eb31e34b0fa0fa

diff --git a/manifest b/manifest
index 43be9dbc63e2a2cd2525d70130688ad3d0557217..251d1e672d52146b7965c89a0936ffc1de6a5628 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Small\ssize\sand\sperformance\sin\sthe\sOP_Column\sopcode.
-D 2017-08-15T14:14:36.511
+C Performance\simprovement\sin\sthe\sOP_Column\sopcode.
+D 2017-08-16T11:04:22.469
 F Makefile.in d9873c9925917cca9990ee24be17eb9613a668012c85a343aef7e5536ae266e8
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc 02b469e9dcd5b7ee63fc1fb05babc174260ee4cfa4e0ef2e48c3c6801567a016
@@ -522,7 +522,7 @@ F src/update.c 5404be9e840717323a69209190cdbc9d0d34adaedaaf1d1a1069babf2c4171c0
 F src/utf.c 810fbfebe12359f10bc2a011520a6e10879ab2a163bcb26c74768eab82ea62a5
 F src/util.c fc081ec6f63448dcd80d3dfad35baecfa104823254a815b081a4d9fe76e1db23
 F src/vacuum.c 90839322fd5f00df9617eb21b68beda9b6e2a2937576b0d65985e4aeb1c53739
-F src/vdbe.c ebfc41ca25465888b2dc2969a0059d0d563c2a36e31696352573198cdec51fad
+F src/vdbe.c 8530c38ffc19400cf9634d2e55b9c6141d276350e6ea6d99a003cd6963fbf20a
 F src/vdbe.h d50cadf12bcf9fb99117ef392ce1ea283aa429270481426b6e8b0280c101fd97
 F src/vdbeInt.h ff2b7db0968d20e6184aee256d2e535d565f5a172e3588a78adb166a41fc4911
 F src/vdbeapi.c 05d6b14ab73952db0d73f6452d6960216997bd966a710266b2fe051f25326abc
@@ -1647,7 +1647,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 373b71d19cad785922d5a80828f2fee0cbe7dff6594743e625bbdfa31b1ca131
-R 36da37536a24b366658dfab60814a38c
+P 2cf3f3de8a48465bd6b0af7763bfe905f3bb0151488f63c9ecc3147bcb345094
+R 1db09713c9077dbfc76327c90333340a
 U drh
-Z 16cc8098bdc3d63f9bef627e24ebd270
+Z 65fa1f244e3ef6aef2172aa886d1ccda

diff --git a/manifest.uuid b/manifest.uuid
index f58cbd3506ba8135ff85949e03e411f725c6976b..5e9b037d4450e04b5ff46266787322c9fd4fa977 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-2cf3f3de8a48465bd6b0af7763bfe905f3bb0151488f63c9ecc3147bcb345094
\ No newline at end of file
+dc98a92f32511ee322b0207bd286e967248a8e59b418f11168eb31e34b0fa0fa
\ No newline at end of file

diff --git a/src/vdbe.c b/src/vdbe.c
index e44f06f3c976e63c9a1ae021b5a8e58e0642365f..c7ef2ef6a14926ef6d5efaf7a19b94f5ad014e2c 100644 (file)
--- a/src/vdbe.c
+++ b/src/vdbe.c
@@ -2464,13 +2464,23 @@ case OP_Column: {
         rc = SQLITE_CORRUPT_BKPT;
         goto abort_due_to_error;
       }
-    }else if( offset>0 ){ /*OPTIMIZATION-IF-TRUE*/
-      /* The following goto is an optimization.  It can be omitted and
-      ** everything will still work.  But OP_Column is measurably faster
-      ** by skipping the subsequent conditional, which is always true.
+    }else{
+      /* This is an optimization.  By skipping over the first few tests
+      ** (ex: pC->nHdrParsed<=p2) in the next section, we achieve a
+      ** measurable performance gain.
+      **
+      ** This branch is taken even if offset==0.  Such a record is never
+      ** generated by SQLite, and could be considered corruption, but we
+      ** accept it for historical reasons.  When offset==0, the code this
+      ** branch jumps to reads past the end of the record, but never more
+      ** than a few bytes.  Even if the record occurs at the end of the page
+      ** content area, the "page header" comes after the page content and so
+      ** this overread is harmless.  Similar overreads can occur for a corrupt
+      ** database file.
       */
       zData = pC->aRow;
       assert( pC->nHdrParsed<=p2 );         /* Conditional skipped */
+      testcase( offset==0 );
       goto op_column_read_header;
     }
   }
@@ -2499,6 +2509,7 @@ case OP_Column: {
       offset64 = aOffset[i];
       zHdr = zData + pC->iHdrOffset;
       zEndHdr = zData + aOffset[0];
+      testcase( zHdr>=zEndHdr );
       do{
         if( (t = zHdr[0])<0x80 ){
           zHdr++;
@@ -2519,9 +2530,14 @@ case OP_Column: {
       if( (zHdr>=zEndHdr && (zHdr>zEndHdr || offset64!=pC->payloadSize))
        || (offset64 > pC->payloadSize)
       ){
-        if( pC->aRow==0 ) sqlite3VdbeMemRelease(&sMem);
-        rc = SQLITE_CORRUPT_BKPT;
-        goto abort_due_to_error;
+        if( aOffset[0]==0 ){
+          i = 0;
+          zHdr = zEndHdr;
+        }else{
+          if( pC->aRow==0 ) sqlite3VdbeMemRelease(&sMem);
+          rc = SQLITE_CORRUPT_BKPT;
+          goto abort_due_to_error;
+        }
       }
 
       pC->nHdrParsed = i;