view tests/cgienv @ 17970:0b03454abae7

ancestor: faster algorithm for difference of ancestor sets

One of the major reasons rebase is slow in large repositories is
the computation of the detach set: the set of ancestors of the
changesets to rebase not in the destination parent. This is currently
done via a revset that does two walks all the way to the root of
the DAG. Instead of doing that, to find ancestors of a set <revs>
not in another set <common> we walk up the tree in reverse revision
number order, maintaining sets of nodes visited from <revs>, <common>
or both.

For the common case where the sets are close both topologically and
in revision number (relative to repository size), this has been
found to speed up rebase by around 15-20%. When the nodes are farther
apart and the DAG is highly branching, it is harder to say which
would win.

Here's how long computing the detach set takes in a linear repository
with over 400000 changesets, rebasing near tip:

Rebasing across 4 changesets
Revset method: 2.2s
New algorithm: 0.00015s

Rebasing across 250 changesets
Revset method: 2.2s
New algorithm: 0.00069s

Rebasing across 10000 changesets
Revset method: 2.4s
New algorithm: 0.019s

DOCUMENT_ROOT="/var/www/hg"; export DOCUMENT_ROOT
GATEWAY_INTERFACE="CGI/1.1"; export GATEWAY_INTERFACE
HTTP_ACCEPT="text/xml,application/xml,application/xhtml+xml,text/html;q=0.9,text/plain;q=0.8,image/png,*/*;q=0.5"; export HTTP_ACCEPT
HTTP_ACCEPT_CHARSET="ISO-8859-1,utf-8;q=0.7,*;q=0.7"; export HTTP_ACCEPT_CHARSET
HTTP_ACCEPT_ENCODING="gzip,deflate"; export HTTP_ACCEPT_ENCODING
HTTP_ACCEPT_LANGUAGE="en-us,en;q=0.5"; export HTTP_ACCEPT_LANGUAGE
HTTP_CACHE_CONTROL="max-age=0"; export HTTP_CACHE_CONTROL
HTTP_CONNECTION="keep-alive"; export HTTP_CONNECTION
HTTP_HOST="hg.omnifarious.org"; export HTTP_HOST
HTTP_KEEP_ALIVE="300"; export HTTP_KEEP_ALIVE
HTTP_USER_AGENT="Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.8.0.4) Gecko/20060608 Ubuntu/dapper-security Firefox/1.5.0.4"; export HTTP_USER_AGENT
PATH_INFO="/"; export PATH_INFO
PATH_TRANSLATED="/var/www/hg/index.html"; export PATH_TRANSLATED
QUERY_STRING=""; export QUERY_STRING
REMOTE_ADDR="127.0.0.2"; export REMOTE_ADDR
REMOTE_PORT="44703"; export REMOTE_PORT
REQUEST_METHOD="GET"; export REQUEST_METHOD
REQUEST_URI="/test/"; export REQUEST_URI
SCRIPT_FILENAME="/home/hopper/hg_public/test.cgi"; export SCRIPT_FILENAME
SCRIPT_NAME="/test"; export SCRIPT_NAME
SCRIPT_URI="http://hg.omnifarious.org/test/"; export SCRIPT_URI
SCRIPT_URL="/test/"; export SCRIPT_URL
SERVER_ADDR="127.0.0.1"; export SERVER_ADDR
SERVER_ADMIN="eric@localhost"; export SERVER_ADMIN
SERVER_NAME="hg.omnifarious.org"; export SERVER_NAME
SERVER_PORT="80"; export SERVER_PORT
SERVER_PROTOCOL="HTTP/1.1"; export SERVER_PROTOCOL
SERVER_SIGNATURE="<address>Apache/2.0.53 (Fedora) Server at hg.omnifarious.org Port 80</address>"; export SERVER_SIGNATURE
SERVER_SOFTWARE="Apache/2.0.53 (Fedora)"; export SERVER_SOFTWARE