svn commit: r1719879 - /subversion/branches/parallel-put/BRANCH-README

[st...@apache.org]

Author: stefan2
Date: Mon Dec 14 10:56:54 2015
New Revision: 1719879

URL: http://svn.apache.org/viewvc?rev=1719879&view=rev
Log:
On the parallel-put branch, add a readme.

* BRANCH-README: new file.

Added:
    subversion/branches/parallel-put/BRANCH-README

Added: subversion/branches/parallel-put/BRANCH-README
URL: http://svn.apache.org/viewvc/subversion/branches/parallel-put/BRANCH-README?rev=1719879&view=auto
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--- subversion/branches/parallel-put/BRANCH-README (added)
+++ subversion/branches/parallel-put/BRANCH-README Mon Dec 14 10:56:54 2015
@@ -0,0 +1,20 @@
+We want to enable Subversion to use multiple concurrent sessions /
+svn_fs_t instances during the data transfer phase of a commit transaction.
+This is to support pipelined processing in http/2, for instance, and should
+eliminate most of the latency penalty for commits with many change or added
+files in them.
+
+Keeping the tree transformation phase of the transaction strictly single-
+threaded, only a small subset of operations needs to support concurrency:
+
+* fs_apply_textdelta
+* fs_apply_text
+* fs_change_node_prop
+
+In concurrent mode, these need to ensure mutally exclusive throughout the
+system, i.e. across threads and processes.  The actual improvement comes
+from the text change functions allowing concurrent writes to the streams
+and delta processors they return.
+
+Because concurrent mode needs a more expensive locking scheme and can't
+use the DAG cache, we want this overhead to be optional.