Modify UPDATE so that two-pass updates on a rowid table use an ephemeral

table to store rowids rather than a RowSet.  This uses less memory, though
it is slower.

FossilOrigin-Name: 4673096dd8c5ed7aed098ff518a6d01d35c40fad991b89fddd91c19a727a4308

manifest

@@ -1,5 +1,5 @@
-C Improved\sdiagnostics\soutput\swith\s".wheretrace\s0x800".\s\sNo\schanges\sto\nnon-debug\sbuilds.
-D 2020-11-12T18:16:01.196
+C Modify\sUPDATE\sso\sthat\stwo-pass\supdates\son\sa\srowid\stable\suse\san\sephemeral\ntable\sto\sstore\srowids\srather\sthan\sa\sRowSet.\s\sThis\suses\sless\smemory,\sthough\nit\sis\sslower.
+D 2020-11-14T20:03:34.128
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -604,7 +604,7 @@ F src/threads.c 4ae07fa022a3dc7c5beb373cf744a85d3c5c6c3c
 F src/tokenize.c 4dc01b267593537e2a0d0efe9f80dabe24c5b6f7627bc6971c487fa6a1dacbbf
 F src/treeview.c 4b92992176fb2caefbe06ba5bd06e0e0ebcde3d5564758da672631f17aa51cda
 F src/trigger.c 515e79206d40d1d4149129318582e79a6e9db590a7b74e226fdb5b2a6c7e1b10
-F src/update.c 1f6167d4acff9f2ae800f7dade84877afbd595c155cdeb7d56f08165d75570c4
+F src/update.c 5d9894b53209e42f57141f1b3d9d86361993049c42b393243abbee0f4bdd49fa
 F src/upsert.c 2920de71b20f04fe25eb00b655d086f0ba60ea133c59d7fa3325c49838818e78
 F src/utf.c ee39565f0843775cc2c81135751ddd93eceb91a673ea2c57f61c76f288b041a0
 F src/util.c c0c7977de7ef9b8cb10f6c85f2d0557889a658f817b0455909a49179ba4c8002
@@ -1883,7 +1883,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 572f1ed59d29e74f810c74ef9e72ebc94c2d3e04befc03a1f88034f04a9c60a8
-R 4901674d935be395f9df3d7654b8445e
+P 772ae83c61c87a9004a614d8ec120ba843286bff1edbd20b987fd592ced84d79
+R 87198020f818dc0e1868a0bdd49e2aaf
+T *branch * lowmem-update-exp
+T *sym-lowmem-update-exp *
+T -sym-trunk *
 U drh
-Z 60f97595458aa54172137f4d47d1e884
+Z 026ca59c1df12878f7c57e2d3cf7ce51

manifest.uuid

@@ -1 +1 @@
-772ae83c61c87a9004a614d8ec120ba843286bff1edbd20b987fd592ced84d79
+4673096dd8c5ed7aed098ff518a6d01d35c40fad991b89fddd91c19a727a4308

src/update.c

@@ -651,6 +651,9 @@ void sqlite3Update(
 
   if( nChangeFrom==0 && HasRowid(pTab) ){
     sqlite3VdbeAddOp3(v, OP_Null, 0, regRowSet, regOldRowid);
+    iEph = pParse->nTab++;
+    addrOpen = sqlite3VdbeAddOp2(v, OP_OpenEphemeral, iEph, 0);
+    sqlite3VdbeLoadString(v, regRowSet, "");
   }else{
     assert( pPk!=0 || HasRowid(pTab) );
     nPk = pPk ? pPk->nKeyCol : 0;
@@ -742,9 +745,10 @@ void sqlite3Update(
       ** leave it in register regOldRowid.  */
       sqlite3VdbeAddOp2(v, OP_Rowid, iDataCur, regOldRowid);
       if( eOnePass==ONEPASS_OFF ){
-        /* We need to use regRowSet, so reallocate aRegIdx[nAllIdx] */
         aRegIdx[nAllIdx] = ++pParse->nMem;
-        sqlite3VdbeAddOp2(v, OP_RowSetAdd, regRowSet, regOldRowid);
+        sqlite3VdbeAddOp3(v, OP_Insert, iEph, regRowSet, regOldRowid);
+      }else{
+        if( addrOpen ) sqlite3VdbeChangeToNoop(v, addrOpen);
       }
     }else{
       /* Read the PK of the current row into an array of registers. In
@@ -832,8 +836,9 @@ void sqlite3Update(
         VdbeCoverage(v);
       }
     }else{
-      labelContinue = sqlite3VdbeAddOp3(v, OP_RowSetRead, regRowSet,labelBreak,
-                               regOldRowid);
+      sqlite3VdbeAddOp2(v, OP_Rewind, iEph, labelBreak); VdbeCoverage(v);
+      labelContinue = sqlite3VdbeMakeLabel(pParse);
+      addrTop = sqlite3VdbeAddOp2(v, OP_Rowid, iEph, regOldRowid);
       VdbeCoverage(v);
       sqlite3VdbeAddOp3(v, OP_NotExists, iDataCur, labelContinue, regOldRowid);
       VdbeCoverage(v);
@@ -1083,11 +1088,11 @@ void sqlite3Update(
   }else if( eOnePass==ONEPASS_MULTI ){
     sqlite3VdbeResolveLabel(v, labelContinue);
     sqlite3WhereEnd(pWInfo);
-  }else if( pPk || nChangeFrom ){
+  }else /*if( pPk || nChangeFrom )*/{
     sqlite3VdbeResolveLabel(v, labelContinue);
     sqlite3VdbeAddOp2(v, OP_Next, iEph, addrTop); VdbeCoverage(v);
-  }else{
-    sqlite3VdbeGoto(v, labelContinue);
+//  }else{
+//    sqlite3VdbeGoto(v, labelContinue);
   }
   sqlite3VdbeResolveLabel(v, labelBreak);