From: drh <>
Date: Wed, 7 Sep 2022 19:28:18 +0000 (+0000)
Subject: An improved technique for ensuring that the Rekey() operation does not
X-Git-Tag: version-3.40.0~206
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8c983ddb670097185d0bd26b11b4e65186192820;p=thirdparty%2Fsqlite.git

An improved technique for ensuring that the Rekey() operation does not
overwrite an existing page number.  This approach does not change the
semantics of the underlying pluggable pcache and it is easier to prove
correct.  This replaces the changes at
[aadd38f99a3e5abc] and [81cff9f1955874aa].

FossilOrigin-Name: 7dbddde79e3ca1b81e00288616fc27434698ce6dcb47714728fce8602ae91f45
---

diff --git a/manifest b/manifest
index e6d926c22b..13721a29d5 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Add\sthe\stool/omittest-msvc.tcl\sscript\sthat\swill\stry\sto\sbuild\susing\sMSVC\nusing\svarious\scompile-time\soptions,\sto\sensure\sthat\sthe\scompile-time\soptions\nall\sbuild\swithout\serrors.
-D 2022-09-05T22:54:36.015
+C An\simproved\stechnique\sfor\sensuring\sthat\sthe\sRekey()\soperation\sdoes\snot\noverwrite\san\sexisting\spage\snumber.\s\sThis\sapproach\sdoes\snot\schange\sthe\nsemantics\sof\sthe\sunderlying\spluggable\spcache\sand\sit\sis\seasier\sto\sprove\ncorrect.\s\sThis\sreplaces\sthe\schanges\sat\n[aadd38f99a3e5abc]\sand\s[81cff9f1955874aa].
+D 2022-09-07T19:28:18.399
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -578,9 +578,9 @@ F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 6176d9752eb580419e8fef4592dc417a6b00ddfd43ee22f818819bf8840ceee8
 F src/pager.h f82e9844166e1585f5786837ddc7709966138ced17f568c16af7ccf946c2baa3
 F src/parse.y 8e67d820030d2655b9942ffe61c1e7e6b96cea2f2f72183533299393907d0564
-F src/pcache.c 22a6ebe498d1d26c85fd1e3bcb246d97b882c060027c1e1688fbea905f5ac3cf
+F src/pcache.c f4268f7f73c6a3db12ce22fd25bc68dc42315d19599414ab1207d7cf32f79197
 F src/pcache.h 4f87acd914cef5016fae3030343540d75f5b85a1877eed1a2a19b9f284248586
-F src/pcache1.c 849a26ea9dc1e6a176b75dc576672a598170b0b46aeef87a981dd25e0af0ccf9
+F src/pcache1.c 5996285f0a1873b1c7925568d1145865105581d588c1671df0c79b43d507174e
 F src/pragma.c 9bf7d8a2a9ad3bc36df3ec0d61817a44c38a1da527d59c26c203047f906e334a
 F src/pragma.h e690a356c18e98414d2e870ea791c1be1545a714ba623719deb63f7f226d8bb7
 F src/prepare.c 971d5819a4bda88038c2283d71fc0a2974ffc3dd480f9bd941341017abacfd1b
@@ -2000,9 +2000,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P f74a5ea8c986dc33d3afcda169c38abbe55728c56716cf9991a5e2ef7fc4917a 82b89f8a074858a81d841dfc26436e8d39ce4907b8f989eba4d848db16758303
-R 6ca49c20c002174082011fae5352b9a2
-T +closed 82b89f8a074858a81d841dfc26436e8d39ce4907b8f989eba4d848db16758303
+P 6b00ecb59fd303f7985902c35a46db9e729201d4beaedea46596b728d9e4b1c8
+R 8bc604264e2fc000e1d53debee8fb293
 U drh
-Z 072f191f34018bff25742e9863a6762e
+Z 8b6d452122c12811257b08bbb3024121
 # Remove this line to create a well-formed Fossil manifest.
diff --git a/manifest.uuid b/manifest.uuid
index 1a48ad4407..15ae82f961 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-6b00ecb59fd303f7985902c35a46db9e729201d4beaedea46596b728d9e4b1c8
\ No newline at end of file
+7dbddde79e3ca1b81e00288616fc27434698ce6dcb47714728fce8602ae91f45
\ No newline at end of file
diff --git a/src/pcache.c b/src/pcache.c
index 8c57f5b1eb..0407e06b2f 100644
--- a/src/pcache.c
+++ b/src/pcache.c
@@ -655,14 +655,14 @@ void sqlite3PcacheMove(PgHdr *p, Pgno newPgno){
   assert( sqlite3PcachePageSanity(p) );
   pcacheTrace(("%p.MOVE %d -> %d\n",pCache,p->pgno,newPgno));
   pOther = sqlite3GlobalConfig.pcache2.xFetch(pCache->pCache, newPgno, 0);
-  sqlite3GlobalConfig.pcache2.xRekey(pCache->pCache, p->pPage, p->pgno,newPgno);
   if( pOther ){
-    PgHdr *pPg = (PgHdr*)pOther->pExtra;
-    pPg->pgno = p->pgno;
-    if( pPg->pPage==0 ){
-      sqlite3GlobalConfig.pcache2.xUnpin(pCache->pCache, pOther, 0);
-    }
+    PgHdr *pXPage = (PgHdr*)pOther->pExtra;
+    assert( pXPage->nRef==0 );
+    pXPage->nRef++;
+    pCache->nRefSum++;
+    sqlite3PcacheDrop(pXPage);
   }
+  sqlite3GlobalConfig.pcache2.xRekey(pCache->pCache, p->pPage, p->pgno,newPgno);
   p->pgno = newPgno;
   if( (p->flags&PGHDR_DIRTY) && (p->flags&PGHDR_NEED_SYNC) ){
     pcacheManageDirtyList(p, PCACHE_DIRTYLIST_FRONT);
diff --git a/src/pcache1.c b/src/pcache1.c
index a47087fa11..551f1b896b 100644
--- a/src/pcache1.c
+++ b/src/pcache1.c
@@ -1125,7 +1125,7 @@ static void pcache1Rekey(
   assert( iOld!=iNew );               /* The page number really is changing */
 
   pcache1EnterMutex(pCache->pGroup);
-  
+
   assert( pcache1FetchNoMutex(p, iOld, 0)==pPage ); /* pPg really is iOld */
   hOld = iOld%pCache->nHash;
   pp = &pCache->apHash[hOld];
@@ -1134,23 +1134,8 @@ static void pcache1Rekey(
   }
   *pp = pPage->pNext;
 
+  assert( pcache1FetchNoMutex(p, iOld, 0)==0 ); /* iOld not in cache */
   hNew = iNew%pCache->nHash;
-  pp = &pCache->apHash[hNew];
-  while( *pp ){
-    if( (*pp)->iKey==iNew ){
-      /* If there is already another pcache entry at iNew, change it to iOld,
-      ** thus swapping the positions of iNew and iOld */
-      PgHdr1 *pOld = *pp;
-      *pp = pOld->pNext;
-      pOld->pNext = pCache->apHash[hOld];
-      pCache->apHash[hOld] = pOld;
-      pOld->iKey = iOld;
-      break;
-    }else{
-      pp = &(*pp)->pNext;
-    }
-  }
-
   pPage->iKey = iNew;
   pPage->pNext = pCache->apHash[hNew];
   pCache->apHash[hNew] = pPage;