Changes to make WAL more robust against SQLITE_PROTOCOL errors.

FossilOrigin-Name: fd578a32f8e9f04957359e73f244a60f02afe08c

diff --git a/manifest b/manifest
index b24ae1e48c47db1d7133fe5c6810c288c2307ee2..7fd8dc68e8d3ca4bec02a1cdbb9446788df1127a 100644 (file)
--- a/manifest
+++ b/manifest
@@ -1,8 +1,8 @@
 -----BEGIN PGP SIGNED MESSAGE-----
 Hash: SHA1
 
-C Fix\sthe\ssqlite3ValueFromExpr()\sroutine\sso\sthat\sit\sreturns\sSQLITE_NOMEM\non\san\sOOM\swhen\strying\sto\sextract\sa\sNULL.
-D 2011-02-18T17:23:23.814
+C Changes\sto\smake\sWAL\smore\srobust\sagainst\sSQLITE_PROTOCOL\serrors.
+D 2011-02-19T15:22:14.943
 F Makefile.arm-wince-mingw32ce-gcc d6df77f1f48d690bd73162294bbba7f59507c72f
 F Makefile.in 27701a1653595a1f2187dc61c8117e00a6c1d50f
 F Makefile.linux-gcc 91d710bdc4998cb015f39edf3cb314ec4f4d7e23
@@ -241,7 +241,7 @@ F src/vdbeblob.c 18955f0ee6b133cd08e1592010cb9a6b11e9984c
 F src/vdbemem.c 0fa2ed786cd207d5b988afef3562a8e663a75b50
 F src/vdbetrace.c 3ba13bc32bdf16d2bdea523245fd16736bed67b5
 F src/vtab.c b297e8fa656ab5e66244ab15680d68db0adbec30
-F src/wal.c aca10a60655e103fc8630a75345000f43c6d47ca
+F src/wal.c 3502efa1febec082dc6e3b250e953a3fcd693ed5
 F src/wal.h 7a5fbb00114b7f2cd40c7e1003d4c41ce9d26840
 F src/walker.c 3112bb3afe1d85dc52317cb1d752055e9a781f8f
 F src/where.c bf8c0f584a2c9becb9110c37e151f9d4f73fbf7e
@@ -910,14 +910,14 @@ F tool/speedtest2.tcl ee2149167303ba8e95af97873c575c3e0fab58ff
 F tool/speedtest8.c 2902c46588c40b55661e471d7a86e4dd71a18224
 F tool/speedtest8inst1.c 293327bc76823f473684d589a8160bde1f52c14e
 F tool/vdbe-compress.tcl d70ea6d8a19e3571d7ab8c9b75cba86d1173ff0f
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-R e75dfeaf15ceeab70c2b4dbe222b0382
+P 1061e94fa983a441b289753b873559163ab849e6
+R 42e1e218d5ef655544f5720fcecf21cc
 U drh
-Z 046db8c28f608cee3392a3f51939415b
+Z d759351aea0417704913e3e155895457
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diff --git a/manifest.uuid b/manifest.uuid
index ec5701e34f9455d4df3ff98ddf50e19755a1e3be..6cb7c128d291d1526d2d8586ae32332875736558 100644 (file)
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-1061e94fa983a441b289753b873559163ab849e6
\ No newline at end of file
+fd578a32f8e9f04957359e73f244a60f02afe08c
\ No newline at end of file

diff --git a/src/wal.c b/src/wal.c
index 34fb6cbbcd6e9e29c5c71913a43feecdfe896585..09573662e9b6f7d5541ba5695a4dc88893d3c84b 100644 (file)
--- a/src/wal.c
+++ b/src/wal.c
@@ -2001,10 +2001,28 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
 
   assert( pWal->readLock<0 );     /* Not currently locked */
 
-  /* Take steps to avoid spinning forever if there is a protocol error. */
+  /* Take steps to avoid spinning forever if there is a protocol error.
+  **
+  ** Circumstances that cause a RETRY should only last for the briefest
+  ** instances of time.  No I/O or other system calls are done while the
+  ** locks are held, so the locks should not be held for very long. But 
+  ** if we are unlucky, another process that is holding a lock might get
+  ** paged out or take a page-fault that is time-consuming to resolve, 
+  ** during the few nanoseconds that it is holding the lock.  In that case,
+  ** it might take longer than normal for the lock to free.
+  **
+  ** After 5 RETRYs, we begin calling sqlite3OsSleep().  The first few
+  ** calls to sqlite3OsSleep() have a delay of 1 microsecond.  Really this
+  ** is more of a scheduler yield than an actual delay.  But on the 10th
+  ** an subsequent retries, the delays start becoming longer and longer, 
+  ** so that on the 100th (and last) RETRY we delay for 21 milliseconds.
+  ** The total delay time before giving up is less than 1 second.
+  */
   if( cnt>5 ){
+    int nDelay = 1;                      /* Pause time in microseconds */
     if( cnt>100 ) return SQLITE_PROTOCOL;
-    sqlite3OsSleep(pWal->pVfs, 1);
+    if( cnt>=10 ) nDelay = (cnt-9)*238;  /* Max delay 21ms. Total delay 996ms */
+    sqlite3OsSleep(pWal->pVfs, nDelay);
   }
 
   if( !useWal ){
@@ -2086,22 +2104,9 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
       mxI = i;
     }
   }
-  if( mxI==0 ){
-    /* If we get here, it means that all of the aReadMark[] entries between
-    ** 1 and WAL_NREADER-1 are zero.  Try to initialize aReadMark[1] to
-    ** be mxFrame, then retry.
-    */
-    rc = walLockExclusive(pWal, WAL_READ_LOCK(1), 1);
-    if( rc==SQLITE_OK ){
-      pInfo->aReadMark[1] = pWal->hdr.mxFrame;
-      walUnlockExclusive(pWal, WAL_READ_LOCK(1), 1);
-      rc = WAL_RETRY;
-    }else if( rc==SQLITE_BUSY ){
-      rc = WAL_RETRY;
-    }
-    return rc;
-  }else{
-    if( mxReadMark < pWal->hdr.mxFrame ){
+  /* There was once an "if" here. The extra "{" is to preserve indentation. */
+  {
+    if( mxReadMark < pWal->hdr.mxFrame || mxI==0 ){
       for(i=1; i<WAL_NREADER; i++){
         rc = walLockExclusive(pWal, WAL_READ_LOCK(i), 1);
         if( rc==SQLITE_OK ){
@@ -2114,6 +2119,10 @@ static int walTryBeginRead(Wal *pWal, int *pChanged, int useWal, int cnt){
         }
       }
     }
+    if( mxI==0 ){
+      assert( rc==SQLITE_BUSY );
+      return WAL_RETRY;
+    }
 
     rc = walLockShared(pWal, WAL_READ_LOCK(mxI));
     if( rc ){
@@ -2491,6 +2500,8 @@ static int walRestartLog(Wal *pWal){
     volatile WalCkptInfo *pInfo = walCkptInfo(pWal);
     assert( pInfo->nBackfill==pWal->hdr.mxFrame );
     if( pInfo->nBackfill>0 ){
+      u32 salt1;
+      sqlite3_randomness(4, &salt1);
       rc = walLockExclusive(pWal, WAL_READ_LOCK(1), WAL_NREADER-1);
       if( rc==SQLITE_OK ){
         /* If all readers are using WAL_READ_LOCK(0) (in other words if no
@@ -2508,7 +2519,7 @@ static int walRestartLog(Wal *pWal){
         pWal->nCkpt++;
         pWal->hdr.mxFrame = 0;
         sqlite3Put4byte((u8*)&aSalt[0], 1 + sqlite3Get4byte((u8*)&aSalt[0]));
-        sqlite3_randomness(4, &aSalt[1]);
+        aSalt[1] = salt1;
         walIndexWriteHdr(pWal);
         pInfo->nBackfill = 0;
         for(i=1; i<WAL_NREADER; i++) pInfo->aReadMark[i] = READMARK_NOT_USED;