internal/postgres: add stats for GetUnit and GetUnitMeta

Additional stats are added to GetUnit and GetUnitMeta to debug latency
issues.

Change-Id: I07abb3191af2e5802670390029f148fa78863679
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/311429
Trust: Julie Qiu <julie@golang.org>
Run-TryBot: Julie Qiu <julie@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jamal Carvalho <jamal@golang.org>

2 files changed, 38 insertions, 20 deletions

diff --git a/internal/postgres/unit.go b/internal/postgres/unit.go
index 8444852b..ac161012 100644
--- a/internal/postgres/unit.go
+++ b/internal/postgres/unit.go
@@ -52,6 +52,7 @@ func (db *DB) GetUnitMeta(ctx context.Context, fullPath, requestedModulePath, re
 
 func (db *DB) getUnitMetaWithKnownLatestVersion(ctx context.Context, fullPath, modulePath, version string, lmv *internal.LatestModuleVersions) (_ *internal.UnitMeta, err error) {
 	defer derrors.WrapStack(&err, "getUnitMetaKnownVersion")
+	defer middleware.ElapsedStat(ctx, "getUnitMetaKnownVersion")()
 
 	query := squirrel.Select(
 		"m.module_path",
@@ -142,6 +143,7 @@ func (db *DB) getLatestUnitVersion(ctx context.Context, fullPath, requestedModul
 	modulePath, latestVersion string, lmv *internal.LatestModuleVersions, err error) {
 
 	defer derrors.WrapStack(&err, "getLatestUnitVersion(%q, %q)", fullPath, requestedModulePath)
+	defer middleware.ElapsedStat(ctx, "getLatestUnitVersion")()
 
 	modPaths := []string{requestedModulePath}
 	// If we don't know the module path, try each possible module path from longest to shortest.
@@ -434,6 +436,7 @@ func (db *DB) getUnitWithAllFields(ctx context.Context, um *internal.UnitMeta) (
 		r      internal.Readme
 		u      internal.Unit
 	)
+	end := middleware.ElapsedStat(ctx, "getUnitWithAllFields-readme-and-imports")
 	err = db.db.QueryRow(ctx, query, um.Path, um.ModulePath, um.Version).Scan(
 		&unitID,
 		database.NullIsEmpty(&r.Filepath),
@@ -451,39 +454,52 @@ func (db *DB) getUnitWithAllFields(ctx context.Context, um *internal.UnitMeta) (
 	default:
 		return nil, err
 	}
+	end()
 
+	// Get documentation.
+	docs, err := db.getDocumentation(ctx, unitID)
+	if err != nil {
+		return nil, err
+	}
+	u.Documentation = docs
+
+	// Get other info.
+	pkgs, err := db.getPackagesInUnit(ctx, um.Path, um.ModulePath, um.Version)
+	if err != nil {
+		return nil, err
+	}
+	u.Subdirectories = pkgs
+	u.UnitMeta = *um
+	return &u, nil
+}
+
+func (db *DB) getDocumentation(ctx context.Context, unitID int) (_ []*internal.Documentation, err error) {
+	defer derrors.WrapStack(&err, "getDocumentation(ctx, %d)", unitID)
+	defer middleware.ElapsedStat(ctx, "getDocumentation")()
+
+	var docs []*internal.Documentation
 	// Get documentation. There can be multiple rows.
-	query = `
+	query := `
 		SELECT goos, goarch, synopsis, source
 		FROM documentation
-		WHERE unit_id = $1
-	`
-	err = db.db.RunQuery(ctx, query, func(rows *sql.Rows) error {
+		WHERE unit_id = $1`
+	if err := db.db.RunQuery(ctx, query, func(rows *sql.Rows) error {
 		var d internal.Documentation
 		if err := rows.Scan(&d.GOOS, &d.GOARCH, &d.Synopsis, &d.Source); err != nil {
 			return err
 		}
-		u.Documentation = append(u.Documentation, &d)
+		docs = append(docs, &d)
 		return nil
-	}, unitID)
-	if err != nil {
+	}, unitID); err != nil {
 		return nil, err
 	}
 	// Sort documentation by GOOS/GOARCH.
-	sort.Slice(u.Documentation, func(i, j int) bool {
-		ci := u.Documentation[i].BuildContext()
-		cj := u.Documentation[j].BuildContext()
+	sort.Slice(docs, func(i, j int) bool {
+		ci := docs[i].BuildContext()
+		cj := docs[j].BuildContext()
 		return internal.CompareBuildContexts(ci, cj) < 0
 	})
-
-	// Get other info.
-	pkgs, err := db.getPackagesInUnit(ctx, um.Path, um.ModulePath, um.Version)
-	if err != nil {
-		return nil, err
-	}
-	u.Subdirectories = pkgs
-	u.UnitMeta = *um
-	return &u, nil
+	return docs, nil
 }
 
 type dbPath struct {
diff --git a/internal/postgres/version.go b/internal/postgres/version.go
index a1bed6d0..76bf5117 100644
--- a/internal/postgres/version.go
+++ b/internal/postgres/version.go
@@ -18,6 +18,7 @@ import (
 	"golang.org/x/pkgsite/internal/database"
 	"golang.org/x/pkgsite/internal/derrors"
 	"golang.org/x/pkgsite/internal/log"
+	"golang.org/x/pkgsite/internal/middleware"
 	"golang.org/x/pkgsite/internal/version"
 	"golang.org/x/sync/errgroup"
 )
@@ -322,7 +323,8 @@ func (db *DB) unitExistsAtLatest(ctx context.Context, unitPath, modulePath strin
 }
 
 func (db *DB) getMultiLatestModuleVersions(ctx context.Context, modulePaths []string) (lmvs []*internal.LatestModuleVersions, err error) {
-	derrors.WrapStack(&err, "getMultiLatestModuleVersions(%v)", modulePaths)
+	defer derrors.WrapStack(&err, "getMultiLatestModuleVersions(%v)", modulePaths)
+	defer middleware.ElapsedStat(ctx, "getMultiLatestModuleVersions")()
 
 	collect := func(rows *sql.Rows) error {
 		var (