svn commit: r1746012 - /subversion/trunk/subversion/libsvn_fs_fs/cached_data.c

[st...@apache.org]

Author: stefan2
Date: Sun May 29 13:35:33 2016
New Revision: 1746012

URL: http://svn.apache.org/viewvc?rev=1746012&view=rev
Log:
In FSFS, prevent the 'block read' mechanism from reading overly long
change lists.  It is the only data structure that needs a potentially
unlimited amount of memory.

The 'block read' feature has been invented to prefetch many small items
that live in the same block of data of e.g. 4 or 64kBytes.  Data larger
that that won't be prefetched unless the call explicitly requested it.

So, we no longer request the changed paths lists but look for them in
the cache instead.  Small ones will likely be there, larger ones will
not have been read at all and the caller reads them from disk as per
usual (no duplicate read etc.).

* subversion/libsvn_fs_fs/cached_data.c
  (svn_fs_fs__get_changes):  No longer ask block-read to return the
                             changes list.
  (block_read_changes): We never return data and, therefore, MUST_READ
                        is implicitly FALSE.
  (block_read): Update caller.

Modified:
    subversion/trunk/subversion/libsvn_fs_fs/cached_data.c

Modified: subversion/trunk/subversion/libsvn_fs_fs/cached_data.c
URL: http://svn.apache.org/viewvc/subversion/trunk/subversion/libsvn_fs_fs/cached_data.c?rev=1746012&r1=1746011&r2=1746012&view=diff
==============================================================================
--- subversion/trunk/subversion/libsvn_fs_fs/cached_data.c (original)
+++ subversion/trunk/subversion/libsvn_fs_fs/cached_data.c Sun May 29 13:35:33 2016
@@ -2939,13 +2939,22 @@ svn_fs_fs__get_changes(apr_array_header_
 
       if (use_block_read(context->fs))
         {
-          /* 'block-read' will also provide us with the desired data */
-          SVN_ERR(block_read((void **)changes, context->fs,
+          /* 'block-read' will probably populate the cache with the data
+           * that we want.  However, we won't want to force it to process
+           * very large change lists as part of this prefetching mechanism.
+           * Those would be better handled by the iterative code below. */
+          SVN_ERR(block_read(NULL, context->fs,
                              context->revision, SVN_FS_FS__ITEM_INDEX_CHANGES,
-                             context->revision_file, result_pool,
+                             context->revision_file, scratch_pool,
                              scratch_pool));
+
+          /* This may succeed now ... */
+          SVN_ERR(svn_cache__get((void **) changes, &found, ffd->changes_cache,
+                                 &context->revision, result_pool));
         }
-      else
+
+      /* If we still have no data, read it here. */
+      if (!found)
         {
           apr_off_t changes_offset;
 
@@ -3364,21 +3373,19 @@ read_item(svn_stream_t **stream,
  * *CHANGES in RESUSLT_POOL and allocate temporaries in SCRATCH_POOL.
  */
 static svn_error_t *
-block_read_changes(apr_array_header_t **changes,
-                   svn_fs_t *fs,
+block_read_changes(svn_fs_t *fs,
                    svn_fs_fs__revision_file_t *rev_file,
                    svn_fs_fs__p2l_entry_t *entry,
-                   svn_boolean_t must_read,
-                   apr_pool_t *result_pool,
                    apr_pool_t *scratch_pool)
 {
   fs_fs_data_t *ffd = fs->fsap_data;
   svn_stream_t *stream;
-  if (!must_read && !ffd->changes_cache)
+  apr_array_header_t *changes;
+  if (!ffd->changes_cache)
     return SVN_NO_ERROR;
 
   /* already in cache? */
-  if (!must_read && ffd->changes_cache)
+  if (ffd->changes_cache)
     {
       svn_boolean_t is_cached;
       SVN_ERR(svn_cache__has_key(&is_cached, ffd->changes_cache,
@@ -3391,13 +3398,12 @@ block_read_changes(apr_array_header_t **
   SVN_ERR(read_item(&stream, fs, rev_file, entry, scratch_pool));
 
   /* read changes from revision file */
-  SVN_ERR(svn_fs_fs__read_changes(changes, stream, INT_MAX,
-                                  result_pool, scratch_pool));
+  SVN_ERR(svn_fs_fs__read_changes(&changes, stream, INT_MAX,
+                                  scratch_pool, scratch_pool));
 
   /* cache for future reference */
-  if (ffd->changes_cache)
-    SVN_ERR(svn_cache__set(ffd->changes_cache, &entry->item.revision,
-                           *changes, scratch_pool));
+  SVN_ERR(svn_cache__set(ffd->changes_cache, &entry->item.revision,
+                         changes, scratch_pool));
 
   return SVN_NO_ERROR;
 }
@@ -3567,10 +3573,8 @@ block_read(void **result,
                     break;
 
                   case SVN_FS_FS__ITEM_TYPE_CHANGES:
-                    SVN_ERR(block_read_changes((apr_array_header_t **)&item,
-                                               fs, revision_file,
-                                               entry, is_result,
-                                               pool, iterpool));
+                    SVN_ERR(block_read_changes(fs, revision_file,
+                                               entry, iterpool));
                     break;
 
                   default: