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Viewing changes to bzrlib/tests/test_btree_index.py

  • Committer: John Arbash Meinel
  • Date: 2009-10-29 16:15:43 UTC
  • mto: This revision was merged to the branch mainline in revision 4780.
  • Revision ID: john@arbash-meinel.com-20091029161543-tdqlm2l4e2z5o7le
We don't have to pad 'short' records.

When writing a row, we reserve 120 bytes from the first node so that we
can write our 'B+Tree Graph Index' signature and other meta-information.
For the root node, we don't always use the 120 bytes, and for non-root
rows, we don't use that data at all. So we usually pad back that
record. However, for indexes that fit entirely in the root record,
we don't pad them to 4096, and it turns out we don't need to pad
them with the spare 120 bytes either.

I was doing a test with lots of 'chained' btree indexes, and this
extra padding ended up being 4.6M => 4.3M of wasted space. I imagine
that bzr-search will have a similar issue with tiny indexes.

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Lines of Context:
bzrlib/tests/test_btree_index.py
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        temp_file = builder.finish()
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        content = temp_file.read()
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        del temp_file
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        self.assertEqual(158, len(content))
 
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        self.assertEqual(131, len(content))
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        self.assertEqual(
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            "B+Tree Graph Index 2\nnode_ref_lists=0\nkey_elements=1\nlen=5\n"
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            "row_lengths=1\n",
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        temp_file = builder.finish()
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        content = temp_file.read()
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        del temp_file
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        self.assertEqual(264, len(content))
 
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        self.assertEqual(238, len(content))
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        self.assertEqual(
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            "B+Tree Graph Index 2\nnode_ref_lists=2\nkey_elements=2\nlen=10\n"
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            "row_lengths=1\n",
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        temp_file = builder.finish()
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        content = temp_file.read()
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        del temp_file
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        self.assertEqual(181, len(content))
 
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        self.assertEqual(155, len(content))
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        self.assertEqual(
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            "B+Tree Graph Index 2\nnode_ref_lists=0\nkey_elements=1\nlen=10\n"
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            "row_lengths=1\n",
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        # The entire index should have been read, as it is one page long.
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        self.assertEqual([('readv', 'index', [(0, size)], False, None)],
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            transport._activity)
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        self.assertEqual(1199, size)
 
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        self.assertEqual(1173, size)
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    def test__read_nodes_no_size_one_page_reads_once(self):
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        self.make_index(nodes=[(('key',), 'value', ())])
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        # The entire index should have been read linearly.
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        self.assertEqual([('readv', 'index', [(0, size)], False, None)],
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            transport._activity)
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        self.assertEqual(1514, size)
 
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        self.assertEqual(1488, size)
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    def test_validate_two_pages(self):
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        builder = btree_index.BTreeBuilder(key_elements=2, reference_lists=2)