Add experimental sqlite3_snapshot_recover() API.

FossilOrigin-Name: 174a6076a8d7bebe5efebf55f3fdc5d87c589cc7

manifest

@@ -1,5 +1,5 @@
-C Require\sthat\sthe\sdatabase\shandle\sbe\sin\sautocommit\smode\sfor\nsqlite3_snapshot_get()\sto\ssucceed.\sThis\sis\sbecause\sit\smay\sopen\sa\sread\ntransaction\son\sthe\sdatabase\sfile.
+C Add\sexperimental\ssqlite3_snapshot_recover()\sAPI.
-D 2016-11-18T18:43:39.100
+D 2016-11-18T20:49:43.736
 F Makefile.in 6b572807415d3f0a379cebc9461416d8df4a12c8
 F Makefile.linux-gcc 7bc79876b875010e8c8f9502eb935ca92aa3c434
 F Makefile.msc bb4d970894abbbe0e88d00aac29bd52af8bc95f4
@@ -352,7 +352,7 @@ F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
 F src/insert.c 0d6e59f9eea62db772eabc0f07901ec26fe01968
 F src/legacy.c 75d3023be8f0d2b99d60f905090341a03358c58e
 F src/loadext.c 5d6642d141c07d366e43d359e94ec9de47add41d
-F src/main.c 602d7179fda1879d688174dcd74c69c8579045b5
+F src/main.c de55e68145758d5512e9397728c9a8f4ff0ffa78
 F src/malloc.c 5ee7c2d3dcb1b0a902c9c6d0115deef54736bdfa
 F src/mem0.c 6a55ebe57c46ca1a7d98da93aaa07f99f1059645
 F src/mem1.c 6919bcf12f221868ea066eec27e579fed95ce98b
@@ -374,8 +374,8 @@ F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
 F src/os_unix.c be9ca0f901a2b6c1bc93dc338f4863675180c189
 F src/os_win.c cf90abd4e50d9f56d2c20ce8e005aff55d7bd8e9
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
-F src/pager.c a31e2c25563065ebfc9308f2ba3a061901fd60a8
+F src/pager.c 4e4aea7ced5734753ccbff4cf4bb4d032cf2173e
-F src/pager.h 07d6938df0b74e4abe8f57807a8b0e1084321d8b
+F src/pager.h d1e944291030351f362a0a7da9b5c3e34e603e39
 F src/parse.y 0338f906b61e311c2b7e11a3f89b0092c780b664
 F src/pcache.c 5ff2a08f76a9c1b22f43eb063b7068fb085465ac
 F src/pcache.h 2cedcd8407eb23017d92790b112186886e179490
@@ -389,7 +389,7 @@ F src/resolve.c bb070cf5f23611c44ab7e4788803684e385fc3fb
 F src/rowset.c 7b7e7e479212e65b723bf40128c7b36dc5afdfac
 F src/select.c 672b1af237ad257149fc5189f3277dcbca036eeb
 F src/shell.c f04e4af75c5517735397d060ed0b4a874104bb41
-F src/sqlite.h.in cc6e3f38d4c1e4df4f569af49c5deb7c32f1ea10
+F src/sqlite.h.in d9b7b5942a18bb83b560c7699aff3925b4f9af90
 F src/sqlite3.rc 5121c9e10c3964d5755191c80dd1180c122fc3a8
 F src/sqlite3ext.h 8648034aa702469afb553231677306cc6492a1ae
 F src/sqliteInt.h c471d791b10c0f2164c8b7a87adc338e703c09cc
@@ -397,7 +397,7 @@ F src/sqliteLimit.h c0373387c287c8d0932510b5547ecde31b5da247
 F src/status.c a9e66593dfb28a9e746cba7153f84d49c1ddc4b1
 F src/table.c 5226df15ab9179b9ed558d89575ea0ce37b03fc9
 F src/tclsqlite.c aef87dcd8cb66564d560ab48d43d19ac812a1eab
-F src/test1.c 58de30ed902f78531cf5cf52b883a26d107208c4
+F src/test1.c d6a047ea534fb68fedcb5a47f4db3baef6748294
 F src/test2.c 3efb99ab7f1fc8d154933e02ae1378bac9637da5
 F src/test3.c d03f5b5da9a2410b7a91c64b0d3306ed28ab6fee
 F src/test4.c 18ec393bb4d0ad1de729f0b94da7267270f3d8e6
@@ -465,8 +465,8 @@ F src/vdbesort.c 91fda3909326860382b0ca8aa251e609c6a9d62c
 F src/vdbetrace.c 41963d5376f0349842b5fc4aaaaacd7d9cdc0834
 F src/vtab.c e02cacb5c7ae742631edeb9ae9f53d399f093fd8
 F src/vxworks.h d2988f4e5a61a4dfe82c6524dd3d6e4f2ce3cdb9
-F src/wal.c 88f8d8adcaecf6a225ae5098062fd151634fb672
+F src/wal.c 5ef877f34c1becb8aaff337bb24544462117a79b
-F src/wal.h bf03a23da3100ab25e5c0363450233cfee09cfc2
+F src/wal.h 06b2a0b599cc0f53ea97f497cf8c6b758c999f71
 F src/walker.c 91a6df7435827e41cff6bb7df50ea00934ee78b0
 F src/where.c 952f76e7a03727480b274b66ca6641b1657cd591
 F src/whereInt.h 2bcc3d176e6091cb8f50a30b65c006e88a73614d
@@ -1103,7 +1103,7 @@ F test/skipscan3.test ec5bab3f81c7038b43450e7b3062e04a198bdbb5
 F test/skipscan5.test 67817a4b6857c47e0e33ba3e506da6f23ef68de2
 F test/skipscan6.test 5866039d03a56f5bd0b3d172a012074a1d90a15b
 F test/snapshot.test 85735bd997a4f6d710140c28fd860519a299649f
-F test/snapshot2.test 30bd95f6fefa8be7f29421e27745cac90b66c74d
+F test/snapshot2.test 26949814860534949672dc007877062719b57c39
 F test/snapshot_fault.test 062ff0438a074978d45e9f9a92e7ad459b74ee73
 F test/soak.test 0b5b6375c9f4110c828070b826b3b4b0bb65cd5f
 F test/softheap1.test 843cd84db9891b2d01b9ab64cef3e9020f98d087
@@ -1535,7 +1535,7 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 1f7ee7af7b620262ae663d65889b6a87415d4a34
+P 83b658dad091211ade3594d1e8d00ce525882506
-R 94e3e6505e79390151b9cd467eca8236
+R 3db63b187961b7fe3d252e007ca73669
 U dan
-Z 084fdf6a46a9563f3a18164c0feb0d49
+Z 5c1ddc1fb889cebc1f3b9de248414272

manifest.uuid

@@ -1 +1 @@
-83b658dad091211ade3594d1e8d00ce525882506
+174a6076a8d7bebe5efebf55f3fdc5d87c589cc7

src/main.c

@@ -4044,6 +4044,34 @@ int sqlite3_snapshot_open(
   return rc;
 }
 
+/*
+** Recover as many snapshots as possible from the wal file associated with
+** schema zDb of database db.
+*/
+int sqlite3_snapshot_recover(sqlite3 *db, const char *zDb){
+  int rc = SQLITE_ERROR;
+  int iDb;
+#ifndef SQLITE_OMIT_WAL
+
+#ifdef SQLITE_ENABLE_API_ARMOR
+  if( !sqlite3SafetyCheckOk(db) ){
+    return SQLITE_MISUSE_BKPT;
+  }
+#endif
+
+  sqlite3_mutex_enter(db->mutex);
+  iDb = sqlite3FindDbName(db, zDb);
+  if( iDb==0 || iDb>1 ){
+    Btree *pBt = db->aDb[iDb].pBt;
+    if( 0==sqlite3BtreeIsInReadTrans(pBt) ){
+      rc = sqlite3PagerSnapshotRecover(sqlite3BtreePager(pBt));
+    }
+  }
+  sqlite3_mutex_leave(db->mutex);
+#endif   /* SQLITE_OMIT_WAL */
+  return rc;
+}
+
 /*
 ** Free a snapshot handle obtained from sqlite3_snapshot_get().
 */

src/pager.c

@@ -7405,6 +7405,20 @@ int sqlite3PagerSnapshotOpen(Pager *pPager, sqlite3_snapshot *pSnapshot){
   }
   return rc;
 }
+
+/*
+** If this is a WAL database, call sqlite3WalSnapshotRecover(). If this 
+** is not a WAL database, return an error.
+*/
+int sqlite3PagerSnapshotRecover(Pager *pPager){
+  int rc;
+  if( pPager->pWal ){
+    rc = sqlite3WalSnapshotRecover(pPager->pWal);
+  }else{
+    rc = SQLITE_ERROR;
+  }
+  return rc;
+}
 #endif /* SQLITE_ENABLE_SNAPSHOT */
 #endif /* !SQLITE_OMIT_WAL */
 

src/pager.h

@@ -182,6 +182,7 @@ int sqlite3PagerSharedLock(Pager *pPager);
 # ifdef SQLITE_ENABLE_SNAPSHOT
   int sqlite3PagerSnapshotGet(Pager *pPager, sqlite3_snapshot **ppSnapshot);
   int sqlite3PagerSnapshotOpen(Pager *pPager, sqlite3_snapshot *pSnapshot);
+  int sqlite3PagerSnapshotRecover(Pager *pPager);
 # endif
 #else
 # define sqlite3PagerUseWal(x) 0

src/sqlite.h.in

@@ -8414,6 +8414,12 @@ SQLITE_EXPERIMENTAL int sqlite3_snapshot_cmp(
   sqlite3_snapshot *p2
 );
 
+/*
+** CAPI3REF: Recover snapshots from a wal file
+** EXPERIMENTAL
+*/
+SQLITE_EXPERIMENTAL int sqlite3_snapshot_recover(sqlite3 *db, const char *zDb);
+
 /*
 ** Undo the hack that converts floating point types to integer for
 ** builds on processors without floating point support.

src/test1.c

@@ -2310,6 +2310,38 @@ static int SQLITE_TCLAPI test_snapshot_get(
 }
 #endif /* SQLITE_ENABLE_SNAPSHOT */
 
+#ifdef SQLITE_ENABLE_SNAPSHOT
+/*
+** Usage: sqlite3_snapshot_recover DB DBNAME
+*/
+static int SQLITE_TCLAPI test_snapshot_recover(
+  void * clientData,
+  Tcl_Interp *interp,
+  int objc,
+  Tcl_Obj *CONST objv[]
+){
+  int rc;
+  sqlite3 *db;
+  char *zName;
+
+  if( objc!=3 ){
+    Tcl_WrongNumArgs(interp, 1, objv, "DB DBNAME");
+    return TCL_ERROR;
+  }
+  if( getDbPointer(interp, Tcl_GetString(objv[1]), &db) ) return TCL_ERROR;
+  zName = Tcl_GetString(objv[2]);
+
+  rc = sqlite3_snapshot_recover(db, zName);
+  if( rc!=SQLITE_OK ){
+    Tcl_SetObjResult(interp, Tcl_NewStringObj(sqlite3ErrName(rc), -1));
+    return TCL_ERROR;
+  }else{
+    Tcl_ResetResult(interp);
+  }
+  return TCL_OK;
+}
+#endif /* SQLITE_ENABLE_SNAPSHOT */
+
 #ifdef SQLITE_ENABLE_SNAPSHOT
 /*
 ** Usage: sqlite3_snapshot_open DB DBNAME SNAPSHOT
@@ -7646,6 +7678,7 @@ int Sqlitetest1_Init(Tcl_Interp *interp){
      { "sqlite3_snapshot_open", test_snapshot_open, 0 },
      { "sqlite3_snapshot_free", test_snapshot_free, 0 },
      { "sqlite3_snapshot_cmp", test_snapshot_cmp, 0 },
+     { "sqlite3_snapshot_recover", test_snapshot_recover, 0 },
      { "sqlite3_snapshot_get_blob", test_snapshot_get_blob, 0 },
      { "sqlite3_snapshot_open_blob", test_snapshot_open_blob, 0 },
      { "sqlite3_snapshot_cmp_blob", test_snapshot_cmp_blob, 0 },

src/wal.c

@@ -2379,6 +2379,65 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
   return rc;
 }
 
+/*
+** Recover as many snapshots as possible from the wal file.
+*/
+int sqlite3WalSnapshotRecover(Wal *pWal){
+  int dummy;
+  int rc;
+
+  rc = sqlite3WalBeginReadTransaction(pWal, &dummy);
+  if( rc==SQLITE_OK ){
+    rc = walLockExclusive(pWal, WAL_CKPT_LOCK, 1);
+    if( rc==SQLITE_OK ){
+      volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
+      int szPage = (int)pWal->szPage;
+      void *pBuf1 = sqlite3_malloc(szPage);
+      void *pBuf2 = sqlite3_malloc(szPage);
+
+      if( pBuf1==0 || pBuf2==0 ){
+        rc = SQLITE_NOMEM;
+      }else{
+        u32 i = pInfo->nBackfillAttempted;
+        for(i=pInfo->nBackfillAttempted; i>pInfo->nBackfill; i--){
+          volatile ht_slot *dummy;
+          volatile u32 *aPgno;      /* Array of page numbers */
+          u32 iZero;                /* Frame corresponding to aPgno[0] */
+          u32 pgno;                 /* Page number in db file */
+          i64 iDbOff;               /* Offset of db file entry */
+          i64 iWalOff;              /* Offset of wal file entry */
+          rc = walHashGet(pWal, walFramePage(i), &dummy, &aPgno, &iZero);
+
+          if( rc==SQLITE_OK ){
+            pgno = aPgno[i-iZero];
+            iDbOff = (i64)(pgno-1) * szPage;
+            iWalOff = walFrameOffset(i, szPage) + WAL_FRAME_HDRSIZE;
+            rc = sqlite3OsRead(pWal->pWalFd, pBuf1, szPage, iWalOff);
+          }
+
+          if( rc==SQLITE_OK ){
+            rc = sqlite3OsRead(pWal->pDbFd, pBuf2, szPage, iDbOff);
+          }
+
+          if( rc!=SQLITE_OK || 0==memcmp(pBuf1, pBuf2, szPage) ){
+            break;
+          }
+
+          pInfo->nBackfillAttempted = i-1;
+        }
+      }
+
+      sqlite3_free(pBuf1);
+      sqlite3_free(pBuf2);
+      walUnlockExclusive(pWal, WAL_CKPT_LOCK, 1);
+    }
+
+    sqlite3WalEndReadTransaction(pWal);
+  }
+
+  return rc;
+}
+
 /*
 ** Begin a read transaction on the database.
 **
@@ -2441,7 +2500,11 @@ int sqlite3WalBeginReadTransaction(Wal *pWal, int *pChanged){
       ** has not yet set the pInfo->nBackfillAttempted variable to indicate 
       ** its intent. To avoid the race condition this leads to, ensure that
       ** there is no checkpointer process by taking a shared CKPT lock 
-      ** before checking pInfo->nBackfillAttempted.  */
+      ** before checking pInfo->nBackfillAttempted.  
+      **
+      ** TODO: Does the aReadMark[] lock prevent a checkpointer from doing
+      **       this already?
+      */
       rc = walLockShared(pWal, WAL_CKPT_LOCK);
 
       if( rc==SQLITE_OK ){

src/wal.h

@@ -131,6 +131,7 @@ int sqlite3WalHeapMemory(Wal *pWal);
 #ifdef SQLITE_ENABLE_SNAPSHOT
 int sqlite3WalSnapshotGet(Wal *pWal, sqlite3_snapshot **ppSnapshot);
 void sqlite3WalSnapshotOpen(Wal *pWal, sqlite3_snapshot *pSnapshot);
+int sqlite3WalSnapshotRecover(Wal *pWal);
 #endif
 
 #ifdef SQLITE_ENABLE_ZIPVFS

test/snapshot2.test

@@ -78,5 +78,65 @@ do_test 1.2.4 {
 execsql COMMIT
 db2 close
 
+#-------------------------------------------------------------------------
+#
+reset_db
+do_execsql_test 2.0 {
+  CREATE TABLE t1(x);
+  PRAGMA journal_mode = wal;
+  INSERT INTO t1 VALUES(1);
+  INSERT INTO t1 VALUES(2);
+} {wal}
+
+do_test 2.1 {
+  db trans { set snap [sqlite3_snapshot_get_blob db main] }
+  sqlite3_db_config db NO_CKPT_ON_CLOSE 1
+  db close
+  sqlite3 db test.db
+
+  execsql {SELECT * FROM sqlite_master}
+  execsql BEGIN
+  sqlite3_snapshot_open_blob db main $snap
+  execsql COMMIT;
+  execsql { INSERT INTO t1 VALUES(3); }
+} {}
+
+do_test 2.2 {
+  sqlite3_db_config db NO_CKPT_ON_CLOSE 1
+  db close
+  sqlite3 db test.db
+
+  execsql {SELECT * FROM sqlite_master}
+  execsql BEGIN
+  list [catch { sqlite3_snapshot_open_blob db main $snap } msg] $msg
+} {1 SQLITE_BUSY_SNAPSHOT}
+
+do_test 2.3 {
+  execsql COMMIT
+  sqlite3_snapshot_recover db main
+  execsql BEGIN
+  sqlite3_snapshot_open_blob db main $snap
+  execsql { SELECT * FROM t1 }
+} {1 2}
+
+do_test 2.4 {
+  execsql COMMIT
+  execsql { SELECT * FROM t1 }
+} {1 2 3}
+
+do_test 2.5 {
+  execsql { PRAGMA wal_checkpoint }
+  sqlite3_db_config db NO_CKPT_ON_CLOSE 1
+  db close
+  sqlite3 db test.db
+
+  execsql {SELECT * FROM sqlite_master}
+  sqlite3_snapshot_recover db main
+  execsql BEGIN
+  list [catch { sqlite3_snapshot_open_blob db main $snap } msg] $msg
+} {1 SQLITE_BUSY_SNAPSHOT}
+
 
 finish_test
+
+