From 7b5507ce4bf4aeb6c9115e7297b053144b153baa Mon Sep 17 00:00:00 2001
From: Julien Pivotto <roidelapluie@inuits.eu>
Date: Fri, 31 Jul 2020 19:11:08 +0200
Subject: [PATCH] Scrape: defer report (#7700)

When I started wotking on target_limit, scrapeAndReport did not exist
yet. Then I simply rebased my work without thinking.

It appears that there is a lot that can be inline if I defer() the
report.

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
---
 scrape/scrape.go | 84 ++++++++++++++++++++++++++----------------------
 1 file changed, 45 insertions(+), 39 deletions(-)

diff --git a/scrape/scrape.go b/scrape/scrape.go
index e21ad9c3a..dce95ae7b 100644
--- a/scrape/scrape.go
+++ b/scrape/scrape.go
@@ -1033,11 +1033,13 @@ func (sl *scrapeLoop) scrapeAndReport(interval, timeout time.Duration, last time
 	}
 
 	b := sl.buffers.Get(sl.lastScrapeSize).([]byte)
+	defer sl.buffers.Put(b)
 	buf := bytes.NewBuffer(b)
 
-	app := sl.appender(sl.ctx)
 	var total, added, seriesAdded int
 	var err, appErr, scrapeErr error
+
+	app := sl.appender(sl.ctx)
 	defer func() {
 		if err != nil {
 			app.Rollback()
@@ -1048,8 +1050,15 @@ func (sl *scrapeLoop) scrapeAndReport(interval, timeout time.Duration, last time
 			level.Error(sl.l).Log("msg", "Scrape commit failed", "err", err)
 		}
 	}()
+
+	defer func() {
+		if err = sl.report(app, start, time.Since(start), total, added, seriesAdded, scrapeErr); err != nil {
+			level.Warn(sl.l).Log("msg", "Appending scrape report failed", "err", err)
+		}
+	}()
+
 	if forcedErr := sl.getForcedError(); forcedErr != nil {
-		appErr = forcedErr
+		scrapeErr = forcedErr
 		// Add stale markers.
 		if _, _, _, err := sl.append(app, []byte{}, "", start); err != nil {
 			app.Rollback()
@@ -1059,53 +1068,50 @@ func (sl *scrapeLoop) scrapeAndReport(interval, timeout time.Duration, last time
 		if errc != nil {
 			errc <- forcedErr
 		}
-	} else {
-		var contentType string
-		scrapeCtx, cancel := context.WithTimeout(sl.ctx, timeout)
-		contentType, scrapeErr = sl.scraper.scrape(scrapeCtx, buf)
-		cancel()
 
-		if scrapeErr == nil {
-			b = buf.Bytes()
-			// NOTE: There were issues with misbehaving clients in the past
-			// that occasionally returned empty results. We don't want those
-			// to falsely reset our buffer size.
-			if len(b) > 0 {
-				sl.lastScrapeSize = len(b)
-			}
-		} else {
-			level.Debug(sl.l).Log("msg", "Scrape failed", "err", scrapeErr.Error())
-			if errc != nil {
-				errc <- scrapeErr
-			}
+		return start
+	}
+
+	var contentType string
+	scrapeCtx, cancel := context.WithTimeout(sl.ctx, timeout)
+	contentType, scrapeErr = sl.scraper.scrape(scrapeCtx, buf)
+	cancel()
+
+	if scrapeErr == nil {
+		b = buf.Bytes()
+		// NOTE: There were issues with misbehaving clients in the past
+		// that occasionally returned empty results. We don't want those
+		// to falsely reset our buffer size.
+		if len(b) > 0 {
+			sl.lastScrapeSize = len(b)
 		}
-
-		// A failed scrape is the same as an empty scrape,
-		// we still call sl.append to trigger stale markers.
-		total, added, seriesAdded, appErr = sl.append(app, b, contentType, start)
-		if appErr != nil {
-			app.Rollback()
-			app = sl.appender(sl.ctx)
-			level.Debug(sl.l).Log("msg", "Append failed", "err", appErr)
-			// The append failed, probably due to a parse error or sample limit.
-			// Call sl.append again with an empty scrape to trigger stale markers.
-			if _, _, _, err := sl.append(app, []byte{}, "", start); err != nil {
-				app.Rollback()
-				app = sl.appender(sl.ctx)
-				level.Warn(sl.l).Log("msg", "Append failed", "err", err)
-			}
+	} else {
+		level.Debug(sl.l).Log("msg", "Scrape failed", "err", scrapeErr.Error())
+		if errc != nil {
+			errc <- scrapeErr
 		}
 	}
 
-	sl.buffers.Put(b)
+	// A failed scrape is the same as an empty scrape,
+	// we still call sl.append to trigger stale markers.
+	total, added, seriesAdded, appErr = sl.append(app, b, contentType, start)
+	if appErr != nil {
+		app.Rollback()
+		app = sl.appender(sl.ctx)
+		level.Debug(sl.l).Log("msg", "Append failed", "err", appErr)
+		// The append failed, probably due to a parse error or sample limit.
+		// Call sl.append again with an empty scrape to trigger stale markers.
+		if _, _, _, err := sl.append(app, []byte{}, "", start); err != nil {
+			app.Rollback()
+			app = sl.appender(sl.ctx)
+			level.Warn(sl.l).Log("msg", "Append failed", "err", err)
+		}
+	}
 
 	if scrapeErr == nil {
 		scrapeErr = appErr
 	}
 
-	if err = sl.report(app, start, time.Since(start), total, added, seriesAdded, scrapeErr); err != nil {
-		level.Warn(sl.l).Log("msg", "Appending scrape report failed", "err", err)
-	}
 	return start
 }