fixup! ZBigFile: Add ZBlk format option 'h' (heuristic) (2)

Rename 'h' to 'auto' and update module documentation accoring to
introduced heuristic. The rename is done because 'h' is not
descriptive, while 'auto' is more descriptive.

bigfile/file_zodb.py

@@ -83,13 +83,18 @@ changes. "Small" here means something like 1-10000 bytes per transaction as
 larger changes become comparable to 2M block size and are handled efficiently
 out of the box. Until the problem is fixed on ZODB server side, wendelin.core
 provides on-client workaround in the form of specialized block format, and
-users have to explicitly indicate via environment variable that their workload
-is "small changes" if they prefer to prioritize database size over access
-speed::
+users can explicitly indicate via environment variable that their workload is
+either "big changes", if they prefer to prioritize access speed, or "small
+changes" if they prefer to prioritize database size over access speed. There is
+also "auto" mode that tries to heuristically use both ZBlk0 and ZBlk1 depending
+on change pattern and works relatively good regrding both access speed and
+database size for append-like workloads::
 
   $WENDELIN_CORE_ZBLK_FMT
-      ZBlk0             fast reads      (default)
+      ZBlk0             fast reads
       ZBlk1             small changes
+      auto  (default)   heuristically use either ZBlk0 or ZBlk1
+                        depending on change pattern
 
 Description of block formats follow:
 
@@ -483,8 +488,8 @@ ZBlk_fmt_registry = {
 }
 
 # format for updated blocks
-ZBlk_fmt_write = os.environ.get('WENDELIN_CORE_ZBLK_FMT', 'h')
-if ZBlk_fmt_write != "h" and ZBlk_fmt_write not in ZBlk_fmt_registry:
+ZBlk_fmt_write = os.environ.get('WENDELIN_CORE_ZBLK_FMT', 'auto')
+if ZBlk_fmt_write != "auto" and ZBlk_fmt_write not in ZBlk_fmt_registry:
     raise RuntimeError('E: Unknown ZBlk format %r' % ZBlk_fmt_write)
 
 
@@ -547,7 +552,7 @@ class ZBigFile(LivePersistent):
     def storeblk(self, blk, buf):
         zblk = self.blktab.get(blk)
         zblk_fmt = ZBlk_fmt_write
-        if zblk_fmt == "h":  # apply heuristic
+        if zblk_fmt == "auto":  # apply heuristic
             zblk_fmt = self._zblk_fmt_heuristic(zblk, blk, buf)
         self._setzblk(blk, zblk, buf, zblk_fmt)
 

bigfile/tests/_test_zblk_fmt

@@ -20,7 +20,7 @@
 #
 # 	- ZBlk0
 # 	- ZBlk1
-# 	- h
+# 	- auto
 
 import os
 import random

bigfile/tests/test-zblk-fmt

@@ -22,9 +22,9 @@
 #
 # 	- ZBlk0
 # 	- ZBlk1
-# 	- h
+# 	- auto
 #
-# The heuristic 'h' should behave as good as ZBlk0 in case of wide changes
+# The heuristic 'auto' should behave as good as ZBlk0 in case of wide changes
 # and as good as ZBlk1 in case of small changes.
 
 function test {
@@ -58,7 +58,7 @@ function test {
 	export arrsize=$arrsize
 	export change_type=$change_type
 
-	t h
+	t auto
 	t ZBlk0
 	t ZBlk1
 

bigfile/tests/test_filezodb.py

@@ -692,16 +692,15 @@ def test_bigfile_zblk1_zdata_reuse():
         assert zdata_v1[i] is zdata_v2[i]
 
 
-# Minimal test to ensure normal operations work as expected
-# with zblk fmt 'h'
+# Minimal test to ensure normal operations work as expected with zblk format 'auto'.
 @func
-def test_bigfile_zblk_fmt_heuristic():
+def test_bigfile_zblk_fmt_auto():
     root = dbopen()
     defer(lambda: dbclose(root))
 
     # set ZBlk_fmt_write to 'h' for this test
     fmt_write_save = file_zodb.ZBlk_fmt_write
-    file_zodb.ZBlk_fmt_write = 'h'
+    file_zodb.ZBlk_fmt_write = 'auto'
     def _():
         file_zodb.ZBlk_fmt_write = fmt_write_save
     defer(_)