Fix a startup race condition that could occur if a wal file grows from 0 bytes while a BEGIN CONCURRENT transaction is running.

FossilOrigin-Name: c1feca4ddaa93fa1cf75e8df061967995a18d726a23f4006d239d3e03c8570df

manifest

@@ -1,5 +1,5 @@
-C Update\sthe\sbegin-concurrent\sbranch\swith\sthe\slatest\senhancements\son\strunk.
-D 2022-12-21T20:07:58.718
+C Fix\sa\sstartup\srace\scondition\sthat\scould\soccur\sif\sa\swal\sfile\sgrows\sfrom\s0\sbytes\swhile\sa\sBEGIN\sCONCURRENT\stransaction\sis\srunning.
+D 2023-01-12T15:30:02.491
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@@ -515,7 +515,7 @@ F ext/wasm/api/sqlite3-api-worker1.js e94ba98e44afccfa482874cd9acb325883ade50ed1
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+F ext/wasm/api/sqlite3-vfs-opfs.c-pp.js 66daf6fb6843bea615fe193109e1542efbeca24f560ee9da63375a910bb48115
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@@ -559,8 +559,8 @@ F ext/wasm/sql/001-sudoku.sql 35b7cb7239ba5d5f193bc05ec379bcf66891bce6f2a5b3879f
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-F ext/wasm/tester1.c-pp.js c45c46cdae1949d426ee12a736087ab180beacc2a20cd829f9052b957adf9ac9 w ext/wasm/tester1.js
+F ext/wasm/tester1.c-pp.html d34bef3d48e5cbc1c7c06882ad240fec49bf88f5f65696cc2c72c416933aa406
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@@ -734,7 +734,7 @@ F src/vdbetrace.c fe0bc29ebd4e02c8bc5c1945f1d2e6be5927ec12c06d89b03ef2a4def34bf8
 F src/vdbevtab.c f99b275366c5fc5e2d99f734729880994ab9500bdafde7fae3b02d562b9d323c
 F src/vtab.c b2f993aa954078985bc40317bb2140fe0880a08a7440f3a428b60fce74636808
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
-F src/wal.c 419c0a98dd65b9419fd07bdd4f9facc61143c33d57b0dbeffd83cf38a2e0e33e
+F src/wal.c 4da9e3c92adba31977cca5960cad1ef51ba1040626a662a8855b3c671b24c422
 F src/wal.h 7ffe787437f20a098af347011967a6d3bb8e5c3dc645e6be59eff44d2b2c5297
 F src/walker.c f890a3298418d7cba3b69b8803594fdc484ea241206a8dfa99db6dd36f8cbb3b
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@@ -896,12 +896,13 @@ F test/columncount.test 6fe99c2f35738b0129357a1cf3fa483f76140f4cd8a89014c88c33c8
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-F test/concurrent3.test 530671ac706f6a1d0f4992dbdd33a86408330d03cd90fb9e82ecb1b27f5fd081
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 F test/conflict3.test 81865d9599609aca394fb3b9cd5f561d4729ea5b176bece3644f6ecb540f88ac
@@ -2083,8 +2084,8 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
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 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P a06d57ee9e2862b2c67dc97e3702c00339341ba308d6558b7694e5b9e47231ac 371f9b88387a44a5f820279d79733d1deb7eafc72f320ec47a11679bbdbb49ef
-R 86b38a0acfb02a8499e4768a9a084653
-U drh
-Z 41f88f8b005a3dfbf678e68c0eda1543
+P 0c198aee53d35cf0999f880c433140c3dfc6bd620c30920b08d7534c0f905e05
+R 6daffe13c1f42c5592d9f7a1cdc6ba09
+U dan
+Z c253903e12da3dd9faf3b286cd9d5110
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-0c198aee53d35cf0999f880c433140c3dfc6bd620c30920b08d7534c0f905e05
+c1feca4ddaa93fa1cf75e8df061967995a18d726a23f4006d239d3e03c8570df

src/wal.c

@@ -3521,7 +3521,11 @@ int sqlite3WalLockForCommit(
 int sqlite3WalUpgradeSnapshot(Wal *pWal){
   int rc = SQLITE_OK;
   assert( pWal->writeLock );
+
+  assert( pWal->szPage==pWal->hdr.szPage );
   memcpy(&pWal->hdr, (void*)walIndexHdr(pWal), sizeof(WalIndexHdr));
+  assert( pWal->szPage==pWal->hdr.szPage || pWal->szPage==0 );
+  pWal->szPage = pWal->hdr.szPage;
 
   /* If this client has its read-lock on slot aReadmark[0] and the entire
   ** wal has not been checkpointed, switch it to a different slot. Otherwise

test/concurrent3.test

@@ -226,6 +226,9 @@ foreach {tn nRepeat oplist} {
   # }
 }
 
+catch { db close }
+sqlite3_shutdown
+test_sqlite3_log
 
 
 finish_test

test/concurrent9.test

@@ -0,0 +1,55 @@
+# 2023 January 12
+#
+# 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.
+#
+
+set testdir [file dirname $argv0]
+source $testdir/tester.tcl
+set testprefix concurrent9
+
+do_execsql_test 1.0 {
+  CREATE TABLE t1(x);
+  INSERT INTO t1 VALUES(1), (2);
+  CREATE TABLE t2(y);
+  INSERT INTO t2 VALUES('a'), ('b');
+  PRAGMA journal_mode = wal;
+} {wal}
+
+db close
+
+#-------------------------------------------------------------------------
+# Fix a problem that may occur if a BEGIN CONCURRENT transaction is 
+# started when the wal file is completely empty and committed after
+# it has been initialized by some other connection.
+#
+sqlite3 db  test.db
+sqlite3 db2 test.db
+
+do_execsql_test -db db  1.1 {
+  BEGIN CONCURRENT;
+    INSERT INTO t2 VALUES('c');
+}
+
+do_execsql_test -db db2  1.2 {
+  INSERT INTO t1 VALUES(3);
+}
+
+do_execsql_test -db db  1.3 {
+  COMMIT;
+}
+
+do_execsql_test -db db2  1.4 {
+  SELECT * FROM t1;
+  SELECT * FROM t2;
+} {1 2 3 a b c}
+
+finish_test
+