Fix a problem causing spurious SQLITE_CORRUPT errors when using the snapshot

API to read from old database snapshots.

FossilOrigin-Name: 535155be584ad8c1836e6b1c62de836d9872056d39608c995221c928cb5b365d

manifest

@@ -1,5 +1,5 @@
-C Add\ssupport\sfor\sthe\sGeopoly\sextension\sto\sthe\sR-Tree\sextension.\s\sThis\salso\ninvolves\sadding\sthe\sSQLITE_INDEX_CONSTRAINT_FUNCTION\scapability\sto\sthe\s\nxFindFunction\smethod\sof\sthe\ssqlite3_module\sobject,\sand\sto\sthe\nsqlite3_index_info.aConstraint.op\sfield\sin\sthe\sxBestIndex\simplementation\sof\nvirtual\stables.
+C Fix\sa\sproblem\scausing\sspurious\sSQLITE_CORRUPT\serrors\swhen\susing\sthe\ssnapshot\nAPI\sto\sread\sfrom\sold\sdatabase\ssnapshots.
-D 2018-08-27T17:13:12.965
+D 2018-08-28T11:23:52.641
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in d06f463c5b623a61ac27f5cb8214fca9e53a6704d34d6b8f2124e2b1b293c88f
@@ -582,7 +582,7 @@ F src/vdbesort.c 90aad5a92608f2dd771c96749beabdb562c9d881131a860a7a5bccf66dc3be7
 F src/vdbetrace.c 79d6dbbc479267b255a7de8080eee6e729928a0ef93ed9b0bfa5618875b48392
 F src/vtab.c 678992ac8ec677a3f9b08126aaf891441083805e3b42574e3654d44538381c14
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
-F src/wal.c e4bcbd90072e9626126d6f3b8411159a0b984c1b9628d15237776578d5eda12d
+F src/wal.c 46bfc9427d527099c17ce00a343a1c3fb8b050b00ddaf90a94398cda44070bf8
 F src/wal.h 606292549f5a7be50b6227bd685fa76e3a4affad71bb8ac5ce4cb5c79f6a176a
 F src/walker.c ba7225773931760cf60bf22f34d0cce2588df7ce5ce0f215a52eb88234b55ac4
 F src/where.c 155809967fbab889374dedf970ea6561b8fb519fcb165d6ba00776552ecc5cde
@@ -1274,6 +1274,7 @@ F test/skipscan6.test 0b4cd1b4ac9f84d91454df513c99a4932fa07e8f27b8049bea605068b3
 F test/snapshot.test fef12fc5c16ff21c4748509401cfba7d9a3d91156f1bfe23fb881d3bfc65ddfe
 F test/snapshot2.test 925e42427e923262db63c9d7155183f889e3e99feaedec4075f659e51608344f
 F test/snapshot3.test 9719443594a04778861bd20d12596c5f880af177d6cd62f111da3198cafc6096
+F test/snapshot4.test 0f7e6bd6f1370d112ee820c541d0dd0e7b8ab4ea77429e65106d81c9ad2185a6
 F test/snapshot_fault.test 52c5e97ebd218846a8ae2da4d147d3e77d71f963
 F test/snapshot_up.test b778a04561a67b8bfde828f473a8d31dbde23e3f648e36237e0369421e08f23c
 F test/soak.test 18944cf21b94a7fe0df02016a6ee1e9632bc4e8d095a0cb49d95e15d5cca2d5c
@@ -1757,8 +1758,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P d158e5b12eec5b81d54c8f5902a972795423947a21d0212b6cceb2810aa6cc5c 4bc28eed32154be0e62fe69acd30f828c2e6f59c6579618ecad8ecf632a90517
+P 666133e32ca8e95807f8437dc8401bc93e2e6508ab8e6ae1e6031b7cee1584ae
-R 8e52d60c2558b132e89c46c2b2e927ee
+R 64c8500a3b3b1576c0a05df68a2057d2
-T +closed 4bc28eed32154be0e62fe69acd30f828c2e6f59c6579618ecad8ecf632a90517
+U dan
-U drh
+Z 4febad62a4c0de1b34fab12b530aa165
-Z 29251fdcd22ade960e4bf01a9382ce41

manifest.uuid

@@ -1 +1 @@
-666133e32ca8e95807f8437dc8401bc93e2e6508ab8e6ae1e6031b7cee1584ae
+535155be584ad8c1836e6b1c62de836d9872056d39608c995221c928cb5b365d

src/wal.c

@@ -2798,6 +2798,7 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
 
         /* Release the shared CKPT lock obtained above. */
         walUnlockShared(pWal, WAL_CKPT_LOCK);
+        pWal->minFrame = 1;
       }
 
 

test/snapshot4.test

@@ -0,0 +1,75 @@
+# 2018 August 28
+#
+# The author disclaims copyright to this source code.  In place of
+# a legal notice, here is a blessing:
+#
+#    May you do good and not evil.
+#    May you find forgiveness for yourself and forgive others.
+#    May you share freely, never taking more than you give.
+#
+#***********************************************************************
+# This file implements regression tests for SQLite library. The focus
+# of this file is the sqlite3_snapshot_xxx() APIs.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+ifcapable !snapshot {finish_test; return}
+set testprefix snapshot4
+
+# This test does not work with the inmemory_journal permutation. The reason
+# is that each connection opened as part of this permutation executes
+# "PRAGMA journal_mode=memory", which fails if the database is in wal mode
+# and there are one or more existing connections.
+if {[permutation]=="inmemory_journal"} {
+  finish_test
+  return
+}
+
+sqlite3 db2 test.db
+
+do_execsql_test 1.0 {
+  PRAGMA cache_size = 10;
+  CREATE TABLE t1(a, b);
+  INSERT INTO t1 VALUES(1, randomblob(400));
+  PRAGMA journal_mode = wal;
+  WITH s(i) AS (
+    SELECT 2 UNION ALL SELECT i+1 FROM s WHERE i<100
+  ) 
+  INSERT INTO t1 SELECT i, randomblob(400) FROM s;
+} {wal}
+
+do_test 1.1 {
+  execsql {
+    BEGIN;
+      SELECT count(*) FROM t1;
+  }
+} {100}
+
+do_test 1.2 {
+  db2 eval { 
+    SELECT count(*) FROM t1;
+    CREATE TABLE t2(x); 
+  }
+} {100}
+
+do_test 1.3 {
+  set ::snap [sqlite3_snapshot_get_blob db main]
+  db2 eval { PRAGMA wal_checkpoint }
+} {0 54 52}
+
+do_test 1.4 {
+  execsql {
+    COMMIT;
+    SELECT * FROM sqlite_master;
+    BEGIN;
+  }
+  sqlite3_snapshot_open_blob db main $::snap
+  execsql {
+    SELECT count(*) FROM t1
+  } 
+} {100}
+
+
+finish_test
+