Author: stefan2
Date: Sat Apr 27 19:50:26 2013
New Revision: 1476661
URL: http://svn.apache.org/r1476661
Log:
On the fsfs-format7 branch: Refine our block stuffing strategy during
pack() to minimize the reads that span more than one block.
* subversion/libsvn_fs_fs/pack.c
(select_block_entries): don't place parsed items near the end of the block;
replace large items overlapping the block boundary
with smaller ones from the next block
Modified:
subversion/branches/fsfs-format7/subversion/libsvn_fs_fs/pack.c
Modified: subversion/branches/fsfs-format7/subversion/libsvn_fs_fs/pack.c
URL:
http://svn.apache.org/viewvc/subversion/branches/fsfs-format7/subversion/libsvn_fs_fs/pack.c?rev=1476661&r1=1476660&r2=1476661&view=diff
==============================================================================
--- subversion/branches/fsfs-format7/subversion/libsvn_fs_fs/pack.c (original)
+++ subversion/branches/fsfs-format7/subversion/libsvn_fs_fs/pack.c Sat Apr 27
19:50:26 2013
@@ -960,16 +960,72 @@ select_block_entries(int *entries_in_blo
/* Estimate extra capacity we will gain from container compression. */
apr_size_t pack_savings = 0;
- /* If the next item does not fit into the current block, auto-pad it. */
+ /* If the next item does not fit into the current block, auto-pad it.
+ Take special care of textual noderevs since their parsers may prefetch
+ up to 80 bytes and we don't want them to cross block boundaries. */
svn_fs_fs__p2l_entry_t *first_entry
= APR_ARRAY_IDX(entries, start_index, svn_fs_fs__p2l_entry_t *);
- if (first_entry->size > capacity_left)
+ apr_off_t safety_margin
+ = first_entry->type == SVN_FS_FS__ITEM_TYPE_NODEREV ? 80 : 0;
+ if (first_entry->size + safety_margin > capacity_left)
{
SVN_ERR(auto_pad_block(context, pool));
capacity_left = ffd->block_size
- (context->pack_offset % ffd->block_size);
}
+ /* try pulling in items from the next block if the first item does not fit
+ but is small enough that it might be packed nicely with the next block.
+ */
+ if ( first_entry->size > capacity_left
+ && first_entry->size < ffd->block_size / 2)
+ {
+ /* frist, try to pull in the first N elements from the next block */
+ apr_off_t pulled_in = 0;
+ for (i = start_index + 1; i < entries->nelts; ++i)
+ {
+ svn_fs_fs__p2l_entry_t *entry
+ = APR_ARRAY_IDX(entries, i, svn_fs_fs__p2l_entry_t *);
+ if ( pulled_in + entry->size > 2 * capacity_left
+ || entry->size > capacity_left)
+ break;
+
+ pulled_in += entry->size;
+ }
+
+ /* if the first one is already to large, look for the largest entry
+ in the next block that still does fit. */
+ if (--i == start_index)
+ {
+ apr_off_t checked = 0;
+ apr_off_t best_size = 0;
+ int best_fit = start_index;
+ for (i = start_index + 1; i < entries->nelts && checked <
ffd->block_size; ++i)
+ {
+ svn_fs_fs__p2l_entry_t *entry
+ = APR_ARRAY_IDX(entries, i, svn_fs_fs__p2l_entry_t *);
+ if (entry->size < capacity_left && entry->size > best_size)
+ {
+ best_fit = i;
+ best_size = entry->size;
+ }
+
+ checked += entry->size;
+ }
+
+ i = best_fit;
+ }
+
+ /* if we found a such entry(es), swap them with the current one. */
+ if (i != start_index)
+ {
+ APR_ARRAY_IDX(entries, start_index, svn_fs_fs__p2l_entry_t *)
+ = APR_ARRAY_IDX(entries, i, svn_fs_fs__p2l_entry_t *);
+ APR_ARRAY_IDX(entries, i, svn_fs_fs__p2l_entry_t *)
+ = first_entry;
+ }
+ }
+
/* try to fit as many items into the current block as possible */
for (i = start_index; i < entries->nelts; ++i)
{
@@ -1070,6 +1126,15 @@ select_block_entries(int *entries_in_blo
SVN_ERR(svn_fs_fs__p2l_proto_index_add_entry
(context->proto_p2l_index, container_entry, pool));
}
+ else if (*entries_in_block > 1)
+ {
+ /* due to the way our parsers prefetch data, it's a bad idea to end
+ * a block with a textual noderev representations */
+ svn_fs_fs__p2l_entry_t *entry
+ = APR_ARRAY_IDX(entries, i - 1, svn_fs_fs__p2l_entry_t *);
+ if (entry->type == SVN_FS_FS__ITEM_TYPE_NODEREV)
+ --*entries_in_block;
+ }
return SVN_NO_ERROR;
}
