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Stop repeating the index check and the history summaries

73ec800beafe53eea186fbc1cebec3306cc49da0 · Keenan Nemetz · 10d ago · parent 5d440e37

Stop repeating the index check and the history summaries

The request memo covered the repository, the open counts and the change
list, but two more reads were repeated:

- The index refresh (issue rows, filters, `#42` numbers) ran on every
  surface that shows one, and each run started by resolving the metadata
  ref. A page calls it from the header, the number lookup and its own
  view, so it now happens once per request, and the resolved commit is
  shared with the change-request read instead of being resolved twice.
- The overview walked the repository's whole history on every load:
  `shortlog` for contributors, `rev-list --count` for the code page's
  commit count, and the tree grouping for languages. Those are properties
  of a commit, and a commit id is content-addressed, so they cannot go
  stale: they are remembered by commit id in a bounded per-process cache
  that evicts oldest-first.

On the fixture (30 change requests, 30 issues) the overview drops from 19
git calls to 9 on a repeated load, the code page from 12 to 11, and every
page loses one `rev-parse` for the metadata ref.

server/web/cache_test.go +47

@@ -0,0 +1,47 @@
	1	package web
	2
	3	import (
	4	"fmt"
	5	"testing"
	6	)
	7
	8	// TestCommitCacheRemembersAndEvicts covers the bound that keeps a repository
	9	// page's history summaries from growing without limit as people browse older
	10	// commits.
	11	func TestCommitCacheRemembersAndEvicts(t *testing.T) {
	12	var c commitCache[int]
	13	if _, ok := c.get("missing"); ok {
	14	t.Fatal("empty cache returned a value")
	15	}
	16	c.put("a", 1)
	17	if v, ok := c.get("a"); !ok \|\| v != 1 {
	18	t.Fatalf("get(a) = %d, %t; want 1, true", v, ok)
	19	}
	20	// A repeated put is not a new entry, so it cannot evict a real one.
	21	c.put("a", 2)
	22	if v, _ := c.get("a"); v != 1 {
	23	t.Fatalf("re-put changed the value to %d", v)
	24	}
	25
	26	for i := 0; i < commitCacheEntries; i++ {
	27	c.put(fmt.Sprintf("k%d", i), i)
	28	}
	29	if _, ok := c.get("a"); ok {
	30	t.Fatal("the oldest entry survived a full cache")
	31	}
	32	if got := len(c.order); got != commitCacheEntries {
	33	t.Fatalf("order holds %d keys, want %d", got, commitCacheEntries)
	34	}
	35	if v, ok := c.get(fmt.Sprintf("k%d", commitCacheEntries-1)); !ok \|\| v != commitCacheEntries-1 {
	36	t.Fatalf("newest entry missing: %d, %t", v, ok)
	37	}
	38	}
	39
	40	// TestCommitKeySeparatesRepositories pins the key: two repositories can hold
	41	// the same commit id, and one's summary must not answer for the other's.
	42	func TestCommitKeySeparatesRepositories(t *testing.T) {
	43	const sha = "0123456789abcdef0123456789abcdef01234567"
	44	if commitKey("/repos/a.git", sha) == commitKey("/repos/b.git", sha) {
	45	t.Fatal("the same commit id in two repositories shares a key")
	46	}
	47	}