Rev 11: Make PAGE_SIZE be a constant, rather than having it hard-coded everywhere. in http://bzr.arbash-meinel.com/plugins/index2

[John Arbash Meinel]

At http://bzr.arbash-meinel.com/plugins/index2

------------------------------------------------------------
revno: 11
revision-id: john at arbash-meinel.com-20080701192734-9mbeqa4zszat3z1f
parent: john at arbash-meinel.com-20080701184228-dhck7vdmkh47zspa
committer: John Arbash Meinel <john at arbash-meinel.com>
branch nick: index2
timestamp: Tue 2008-07-01 14:27:34 -0500
message:
  Make PAGE_SIZE be a constant, rather than having it hard-coded everywhere.
-------------- next part --------------
=== modified file 'btree_index.py'
--- a/btree_index.py	2008-07-01 11:37:43 +0000
+++ b/btree_index.py	2008-07-01 19:27:34 +0000
@@ -33,6 +33,8 @@
 _INTERNAL_FLAG = "type=internal\n"
 _INTERNAL_OFFSET = "offset="
 
+_PAGE_SIZE = 4096
+
 
 class _BuilderRow(object):
     """The stored state accumulated while writing out a row in the index.
@@ -103,7 +105,8 @@
                     # padded note:
                     row.spool.write("\x00" * 100)
                 row.spool.writelines(byte_lines)
-                if row.spool.tell() % 4096 != 0:
+                if row.spool.tell() % _PAGE_SIZE != 0:
+                    import pdb; pdb.set_trace()
                     raise AssertionError("incorrect node length")
                 row.nodes += 1
                 row.writer = None
@@ -120,7 +123,7 @@
                         # flesh out any internal nodes that are needed to
                         # preserve the high of the tree
                         if internal_row.writer is None:
-                            length = 4096
+                            length = _PAGE_SIZE
                             if internal_row.nodes == 0:
                                 length -= 100 # padded
                             internal_row.writer = chunk_writer.ChunkWriter(
@@ -129,7 +132,7 @@
                             internal_row.writer.write(_INTERNAL_OFFSET +
                                 str(self.rows[pos + 1].nodes) + "\n")
                     # add a new leaf
-                    length = 4096
+                    length = _PAGE_SIZE
                     if self.rows[-1].nodes == 0:
                         length -= 100 # padded
                     self.rows[-1].writer = chunk_writer.ChunkWriter(length)
@@ -155,7 +158,8 @@
                         # We need a new row
                         new_row = _BuilderRow()
                         self.rows.insert(0, new_row)
-                        new_row.writer = chunk_writer.ChunkWriter(3996)
+                        # This will be padded, hence the -100
+                        new_row.writer = chunk_writer.ChunkWriter(_PAGE_SIZE - 100)
                         new_row.writer.write(_INTERNAL_FLAG)
                         new_row.writer.write(_INTERNAL_OFFSET +
                             str(self.rows[1].nodes - 1) + "\n")
@@ -194,12 +198,12 @@
             row.spool.seek(0)
             # copy nodes to the finalised file.
             # Special case the first node as it may be prefixed
-            node = row.spool.read(4096)
+            node = row.spool.read(_PAGE_SIZE)
             result.write(node[reserved:])
             result.write("\x00" * (reserved - position))
             position = 0 # Only the root row actually has an offset
             copied_len = osutils.pumpfile(row.spool, result)
-            if copied_len != (row.nodes - 1) * 4096:
+            if copied_len != (row.nodes - 1) * _PAGE_SIZE:
                 import pdb;pdb.set_trace()
                 raise AssertionError("Not enough data copied")
         result.flush()
@@ -488,18 +492,18 @@
         """
         ranges = []
         for index in nodes:
-            offset = index * 4096
-            size = 4096
+            offset = index * _PAGE_SIZE
+            size = _PAGE_SIZE
             if index == 0:
                 # Root node - special case
                 if self._size:
-                    size = min(4096, self._size)
+                    size = min(_PAGE_SIZE, self._size)
                 else:
                     stream = self._transport.get(self._name)
-                    start = stream.read(4096)
+                    start = stream.read(_PAGE_SIZE)
                     # Avoid doing this again
                     self._size = len(start)
-                    size = min(4096, self._size)
+                    size = min(_PAGE_SIZE, self._size)
             ranges.append((offset, size))
         for offset, data in self._transport.readv(self._name, ranges):
             if offset == 0:
@@ -514,7 +518,7 @@
                 node = _InternalNode(bytes)
             else:
                 raise AssertionError("Unknown node type for %r" % bytes)
-            yield offset / 4096, node
+            yield offset / _PAGE_SIZE, node
 
     def _signature(self):
         """The file signature for this index type."""