gitweb: cache $parent_commit info in git_blame()
Luben Tuikov changed 'lineno' link from leading to commit which gave current version of given block of lines, to leading to parent of this commit in 244a70e6 (Blame "linenr" link jumps to previous state at "orig_lineno"). This made possible data mining using 'blame' view. The current implementation calls rev-parse once per each blamed line to find parent revision of blamed commit, even when the same commit appears more than once, which is inefficient. This patch mitigates this issue by caching $parent_commit info in %metainfo, which makes gitweb call rev-parse only once per each unique commit in the output from "git blame". In the tables below you can see simple benchmark comparing gitweb performance before and after this patch File | L[1] | C[2] || Time0[3] | Before[4] | After[4] ==================================================================== blob.h | 18 | 4 || 0m1.727s | 0m2.545s | 0m2.474s GIT-VERSION-GEN | 42 | 13 || 0m2.165s | 0m2.448s | 0m2.071s README | 46 | 6 || 0m1.593s | 0m2.727s | 0m2.242s revision.c | 1923 | 121 || 0m2.357s | 0m30.365s | 0m7.028s gitweb/gitweb.perl | 6291 | 428 || 0m8.080s | 1m37.244s | 0m20.627s File | L/C | Before/After ========================================= blob.h | 4.5 | 1.03 GIT-VERSION-GEN | 3.2 | 1.18 README | 7.7 | 1.22 revision.c | 15.9 | 4.32 gitweb/gitweb.perl | 14.7 | 4.71 As you can see the greater ratio of lines in file to unique commits in blame output, the greater gain from the new implementation. Legend: [1] Number of lines: $ wc -l <file> [2] Number of unique commits in the blame output: $ git blame -p <file> | grep author-time | wc -l [3] Time for running "git blame -p" (user time, single run): $ time git blame -p <file> >/dev/null [4] Time to run gitweb as Perl script from command line: $ gitweb-run.sh "p=.git;a=blame;f=<file>" > /dev/null 2>&1 The gitweb-run.sh script includes slightly modified (with adjusted pathnames) code from gitweb_run() function from the test script t/t9500-gitweb-standalone-no-errors.sh; gitweb config file gitweb_config.perl contents (again up to adjusting pathnames; in particular $projectroot variable should point to top directory of git repository) can be found in the same place. Discussion ~~~~~~~~~~ A possible future improvement would be to open a bidi pipe to "git cat-file --batch-check", (like in Git::Repo in gitweb caching by Lea Wiemann), feed $long_rev^ to it, and parse its output, which is in the following form: 926b07e694599d86cec668475071b32147c95034 commit 637 This would mean one call to git-cat-file for the whole 'blame' view, instead of one call to git-rev-parse per each unique commit in blame output. Yet another solution would be to change use of validate_refname() to validate_revision() when checking script parameters (CGI query or path_info), with validate_revision being something like the following: sub validate_revision { my $rev = shift; return validate_refname(strip_rev_suffixes($rev)); } so we don't need to calculate $long_rev^, but can pass "$long_rev^" as 'hb' parameter. This solution has the advantage that it can be easily adapted to future incremental blame output. Signed-off-by: NJakub Narebski <jnareb@gmail.com> Acked-by: NLuben Tuikov <ltuikov@yahoo.com> Signed-off-by: NJunio C Hamano <gitster@pobox.com>
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