changeset 5451:0a43875677b1

revlog: break up compression of large deltas Python's zlib apparently makes an internal copy of strings passed to compress(). To avoid this, compress strings 1M at a time, then join them at the end if the result would be smaller than the original. For initial commits of large but compressible files, this cuts peak memory usage nearly in half.
author Matt Mackall <mpm@selenic.com>
date Thu, 11 Oct 2007 00:46:54 -0500
parents c728424d44c6
children 82b4ff3abbcd
files mercurial/revlog.py
diffstat 1 files changed, 18 insertions(+), 3 deletions(-) [+]
line wrap: on
line diff
--- a/mercurial/revlog.py	Thu Oct 11 00:46:53 2007 -0500
+++ b/mercurial/revlog.py	Thu Oct 11 00:46:54 2007 -0500
@@ -61,12 +61,27 @@
     """ generate a possibly-compressed representation of text """
     if not text:
         return ("", text)
-    if len(text) < 44:
+    l = len(text)
+    if l < 44:
         if text[0] == '\0':
             return ("", text)
         return ('u', text)
-    bin = _compress(text)
-    if len(bin) > len(text):
+    elif l > 1000000:
+        # zlib makes an internal copy, thus doubling memory usage for
+        # large files, so lets do this in pieces
+        z = zlib.compressobj()
+        p = []
+        pos = 0
+        while pos < l:
+            pos2 = pos + 2**20
+            p.append(z.compress(text[pos:pos2]))
+            pos = pos2
+        p.append(z.flush())
+        if sum(map(len, p)) < l:
+            bin = "".join(p)
+    else:
+        bin = _compress(text)
+    if len(bin) > l:
         if text[0] == '\0':
             return ("", text)
         return ('u', text)