From: drh <drh@noemail.net>
Date: Thu, 15 Feb 2018 20:00:53 +0000 (+0000)
Subject: On unix, the "PRAGMA fsync_interval=N" command causes an extra fdatasync()
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=refs%2Fheads%2Fwrite-queue-flush-hack;p=thirdparty%2Fsqlite.git

On unix, the "PRAGMA fsync_interval=N" command causes an extra fdatasync()
after writing N bytes of content, to force a write-queue flush in the
underlying OS.  This is an experimental hack that is not expected to land
on trunk.

FossilOrigin-Name: b18cc5fee44fb2ab8a48fb3ba92a780090c7ead6af1ebcb67ab1fe214dde709c
---

diff --git a/manifest b/manifest
index d23be9ea5b..8469b0d573 100644
--- a/manifest
+++ b/manifest
@@ -1,5 +1,5 @@
-C Fix\sanother\spoint\sin\szonefile.c\sso\sthat\sall\sfiles\sare\sopened\sin\seither\s"rb"\sor\n"wb"\smode.
-D 2018-02-15T15:24:12.092
+C On\sunix,\sthe\s"PRAGMA\sfsync_interval=N"\scommand\scauses\san\sextra\sfdatasync()\nafter\swriting\sN\sbytes\sof\scontent,\sto\sforce\sa\swrite-queue\sflush\sin\sthe\nunderlying\sOS.\s\sThis\sis\san\sexperimental\shack\sthat\sis\snot\sexpected\sto\sland\non\strunk.
+D 2018-02-15T20:00:53.163
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F Makefile.in 7a3f714b4fcf793108042b7b0a5c720b0b310ec84314d61ba7f3f49f27e550ea
@@ -475,7 +475,7 @@ F src/os.c 22d31db3ca5a96a408fbf1ceeaaebcaf64c87024d2ff9fe1cf2ddbec3e75c104
 F src/os.h 48388821692e87da174ea198bf96b1b2d9d83be5dfc908f673ee21fafbe0d432
 F src/os_common.h b2f4707a603e36811d9b1a13278bffd757857b85
 F src/os_setup.h 0dbaea40a7d36bf311613d31342e0b99e2536586
-F src/os_unix.c ce491421b3a54b63094a155eeac668a3bc8e5b86a5a58551d906e5b5affb443f
+F src/os_unix.c 774c789b63aaa4f3e17f5348a336c60bbd94f43e1aeb0a2bc4ffffe60fc178d3
 F src/os_win.c eb03c6d52f893bcd7fdd4c6006674c13c1b5e49543fec98d605201af2997171c
 F src/os_win.h 7b073010f1451abe501be30d12f6bc599824944a
 F src/pager.c 0b6bd5442733b2e08d0673de6cdafe3e7ab0b5715e4844ac836ab346b1d9ed89
@@ -1708,7 +1708,10 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 4bb854ddd9c1dc2972fd4f7c2c2b2d121caa662d5085694c2dbb35d331a61444
-R 2c56f94b965e90e1ed8c01e5183c20c8
-U dan
-Z 2cff9a10fd106f92fe182af0aacf7c32
+P fb1c2277912c55cfae30c18b5434bc193748746395fa7df983cd8a29e5741ff9
+R de6bec149ec0467cfe04c10e1715419d
+T *branch * write-queue-flush-hack
+T *sym-write-queue-flush-hack *
+T -sym-zonefile *
+U drh
+Z 7c64ce09377dd8ff73b08359bba5f163
diff --git a/manifest.uuid b/manifest.uuid
index da03a2339e..5bb3838738 100644
--- a/manifest.uuid
+++ b/manifest.uuid
@@ -1 +1 @@
-fb1c2277912c55cfae30c18b5434bc193748746395fa7df983cd8a29e5741ff9
\ No newline at end of file
+b18cc5fee44fb2ab8a48fb3ba92a780090c7ead6af1ebcb67ab1fe214dde709c
\ No newline at end of file
diff --git a/src/os_unix.c b/src/os_unix.c
index b24c6861d3..b885201910 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -209,6 +209,10 @@ struct unixFile {
   unsigned char eFileLock;            /* The type of lock held on this fd */
   unsigned short int ctrlFlags;       /* Behavioral bits.  UNIXFILE_* flags */
   int lastErrno;                      /* The unix errno from last I/O error */
+#ifdef SQLITE_WRITE_QUEUE_FLUSH_HACK
+  unsigned int nUnsyncWrite;          /* Bytes written since last fsync() */
+  unsigned int nUnsyncLimit;          /* Maximum bytes written before fsync() */
+#endif
   void *lockingContext;               /* Locking style specific state */
   UnixUnusedFd *pPreallocatedUnused;  /* Pre-allocated UnixUnusedFd */
   const char *zPath;                  /* Name of the file */
@@ -3368,7 +3372,18 @@ static int unixWrite(
   }
 #endif
  
-  while( (wrote = seekAndWrite(pFile, offset, pBuf, amt))<amt && wrote>0 ){
+  while( 1 ){
+    wrote = seekAndWrite(pFile, offset, pBuf, amt);
+#ifdef SQLITE_WRITE_QUEUE_FLUSH_HACK
+    if( pFile->nUnsyncLimit ){
+      pFile->nUnsyncWrite += wrote;
+      if( pFile->nUnsyncWrite>=pFile->nUnsyncLimit ){
+        fdatasync(pFile->h);
+        pFile->nUnsyncWrite = 0;
+      }
+    }
+#endif
+    if( wrote>=amt || wrote<=0 ) break;
     amt -= wrote;
     offset += wrote;
     pBuf = &((char*)pBuf)[wrote];
@@ -3597,6 +3612,9 @@ static int unixSync(sqlite3_file *id, int flags){
   assert( pFile );
   OSTRACE(("SYNC    %-3d\n", pFile->h));
   rc = full_fsync(pFile->h, isFullsync, isDataOnly);
+#ifdef SQLITE_WRITE_QUEUE_FLUSH_HACK
+  pFile->nUnsyncWrite = 0;
+#endif
   SimulateIOError( rc=1 );
   if( rc ){
     storeLastErrno(pFile, errno);
@@ -3818,6 +3836,17 @@ static int unixFileControl(sqlite3_file *id, int op, void *pArg){
     }
 #endif /* __linux__ && SQLITE_ENABLE_BATCH_ATOMIC_WRITE */
 
+#ifdef SQLITE_WRITE_QUEUE_FLUSH_HACK
+    case SQLITE_FCNTL_PRAGMA: {
+      char **azParam = (char**)pArg;
+      if( sqlite3_stricmp(azParam[1],"fsync_interval")==0 ){
+        pFile->nUnsyncLimit = atoi(azParam[2]);
+        return SQLITE_OK;
+      }
+      return SQLITE_NOTFOUND;
+    }
+#endif
+
     case SQLITE_FCNTL_LOCKSTATE: {
       *(int*)pArg = pFile->eFileLock;
       return SQLITE_OK;