--- a/mercurial-agent/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/ext/impl/SparseCheckoutProvider.java	Fri Aug 22 20:52:31 2014 +0200
+++ b/mercurial-agent/src/jetbrains/buildServer/buildTriggers/vcs/mercurial/ext/impl/SparseCheckoutProvider.java	Mon Aug 25 16:28:24 2014 +0200
@@ -95,21 +95,24 @@
     }
 
     public void call(@NotNull HgRepo repo, @NotNull String revision) throws VcsException {
-      writeSparseConfig(repo.getWorkingDir());
+      String currentConfig = readSparseContent(repo.getWorkingDir());
+      String newConfig = getSparseContentFromRules();
+      if (currentConfig.equals(newConfig))
+        return;
+      writeSparseConfig(repo.getWorkingDir(), newConfig);
       repo.runCommand("sparse", "--refresh");
     }
 
-    private void writeSparseConfig(@NotNull File workingDir) throws VcsException {
-      String sparse = getSparseContent();
+    private void writeSparseConfig(@NotNull File workingDir, @NotNull String sparseContent) throws VcsException {
       try {
-        FileUtil.writeToFile(new File(new File(workingDir, ".hg"), "sparse"), sparse.getBytes("UTF-8"), false);
+        FileUtil.writeToFile(getSparseConfig(workingDir), sparseContent.getBytes("UTF-8"), false);
       } catch (IOException e) {
         Loggers.VCS.warn("Error while writing .hg/sparse, will not do a sparse checkout", e);
       }
     }
 
     @NotNull
-    private String getSparseContent() {
+    private String getSparseContentFromRules() {
       StringBuilder sparse = new StringBuilder();
       sparse.append("[exclude]\n");
       for (FileRule rule : myRules.getExcludeRules()) {
@@ -117,13 +120,26 @@
       }
       return sparse.toString();
     }
+
+    @NotNull
+    private String readSparseContent(@NotNull File workingDir) {
+      File sparseConfig = getSparseConfig(workingDir);
+      if (!sparseConfig.exists())
+        return "";
+      try {
+        return FileUtil.readText(sparseConfig);
+      } catch (IOException e) {
+        Loggers.VCS.warn("Error while reading .hg/sparse, assume it was empty", e);
+        return "";
+      }
+    }
   }
 
 
   private static class UndoSparseCheckout implements BeforeWorkingDirUpdateExtension {
     public void call(@NotNull HgRepo repo, @NotNull String revision) throws VcsException {
       File workingDir = repo.getWorkingDir();
-      File sparseConfig = new File(new File(workingDir, ".hg"), "sparse");
+      File sparseConfig = getSparseConfig(workingDir);
       if (sparseConfig.exists()) {
         Loggers.VCS.info("Remove sparse extension config and reset working directory state");
         FileUtil.delete(sparseConfig);
@@ -131,4 +147,9 @@
       }
     }
   }
+
+
+  private static File getSparseConfig(@NotNull File workingDir) {
+    return new File(new File(workingDir, ".hg"), "sparse");
+  }
 }