diff --git a/monitoring/go/alertserver/main.go b/monitoring/go/alertserver/main.go
index a8a9c8c..680ee6b 100644
--- a/monitoring/go/alertserver/main.go
+++ b/monitoring/go/alertserver/main.go
@@ -14,6 +14,7 @@
 	"os/user"
 	"path/filepath"
 	"runtime"
+	"strconv"
 	"strings"
 	"time"
 )
@@ -33,12 +34,14 @@
 	"skia.googlesource.com/buildbot.git/go/skiaversion"
 	"skia.googlesource.com/buildbot.git/go/util"
 	"skia.googlesource.com/buildbot.git/monitoring/go/alerting"
+	"skia.googlesource.com/buildbot.git/monitoring/go/commit_cache"
 )
 
 const (
 	COOKIESALT_METADATA_KEY          = "cookiesalt"
 	CLIENT_ID_METADATA_KEY           = "client_id"
 	CLIENT_SECRET_METADATA_KEY       = "client_secret"
+	DEFAULT_COMMITS_TO_LOAD          = 35
 	INFLUXDB_NAME_METADATA_KEY       = "influxdb_name"
 	INFLUXDB_PASSWORD_METADATA_KEY   = "influxdb_password"
 	GMAIL_CLIENT_ID_METADATA_KEY     = "gmail_clientid"
@@ -48,8 +51,9 @@
 )
 
 var (
-	alertManager *alerting.AlertManager = nil
-	gitInfo      *gitinfo.GitInfo       = nil
+	alertManager *alerting.AlertManager    = nil
+	gitInfo      *gitinfo.GitInfo          = nil
+	commitCache  *commit_cache.CommitCache = nil
 )
 
 // flags
@@ -77,6 +81,19 @@
 	return false
 }
 
+func getIntParam(name string, r *http.Request) (*int, error) {
+	raw, ok := r.URL.Query()[name]
+	if !ok {
+		return nil, nil
+	}
+	v64, err := strconv.ParseInt(raw[0], 10, 32)
+	if err != nil {
+		return nil, fmt.Errorf("Invalid value for parameter %q: %s -- %v", name, raw, err)
+	}
+	v32 := int(v64)
+	return &v32, nil
+}
+
 func alertJsonHandler(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json")
 	type displayAlert struct {
@@ -174,31 +191,40 @@
 
 func commitsJsonHandler(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json")
-	gitInfo.Update(true, true)
-	commitHashes := gitInfo.From(time.Now().AddDate(0, 0, -45))
-	branchHeads, err := gitInfo.GetBranches()
+	// Case 1: Requesting specific commit range by index.
+	startIdx, err := getIntParam("start", r)
 	if err != nil {
-		util.ReportError(w, r, err, fmt.Sprintf("Failed to read branch information from the repo: %s", err))
+		util.ReportError(w, r, err, fmt.Sprintf("Invalid parameter: %v", err))
 		return
 	}
-	commits := make([]*gitinfo.LongCommit, len(commitHashes))
-	for i, h := range commitHashes {
-		c, err := gitInfo.Details(h)
+	if startIdx != nil {
+		endIdx := commitCache.NumCommits()
+		end, err := getIntParam("end", r)
 		if err != nil {
-			util.ReportError(w, r, err, fmt.Sprintf("Failed to obtain commit details for %s: %s", h, err))
+			util.ReportError(w, r, err, fmt.Sprintf("Invalid parameter: %v", err))
 			return
 		}
-		commits[i] = c
+		if end != nil {
+			endIdx = *end
+		}
+		if err := commitCache.RangeAsJson(w, *startIdx, endIdx); err != nil {
+			util.ReportError(w, r, err, fmt.Sprintf("Failed to load commit range from cache: %v", err))
+			return
+		}
+		return
 	}
-	data := struct {
-		Commits     []*gitinfo.LongCommit `json:"commits"`
-		BranchHeads []*gitinfo.GitBranch  `json:"branch_heads"`
-	}{
-		Commits:     commits,
-		BranchHeads: branchHeads,
+	// Case 2: Requesting N (or the default number) commits.
+	commitsToLoad := DEFAULT_COMMITS_TO_LOAD
+	n, err := getIntParam("n", r)
+	if err != nil {
+		util.ReportError(w, r, err, fmt.Sprintf("Invalid parameter: %v", err))
+		return
 	}
-	if err := json.NewEncoder(w).Encode(data); err != nil {
-		util.ReportError(w, r, err, fmt.Sprintf("Failed to encode commit data as JSON: %s", err))
+	if n != nil {
+		commitsToLoad = *n
+	}
+	if err := commitCache.LastNAsJson(w, commitsToLoad); err != nil {
+		util.ReportError(w, r, err, fmt.Sprintf("Failed to load commits from cache: %v", err))
 		return
 	}
 }
@@ -308,5 +334,16 @@
 	if err != nil {
 		glog.Fatalf("Failed to check out Skia: %v", err)
 	}
+	commitCache, err = commit_cache.New(gitInfo)
+	if err != nil {
+		glog.Fatalf("Failed to create commit cache: %v", err)
+	}
+	go func() {
+		for _ = range time.Tick(time.Minute) {
+			if err := commitCache.Update(); err != nil {
+				glog.Errorf("Failed to update commit cache: %v", err)
+			}
+		}
+	}()
 	runServer(serverURL)
 }
diff --git a/monitoring/go/commit_cache/commit_cache.go b/monitoring/go/commit_cache/commit_cache.go
new file mode 100644
index 0000000..47805ba
--- /dev/null
+++ b/monitoring/go/commit_cache/commit_cache.go
@@ -0,0 +1,126 @@
+package commit_cache
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"sync"
+	"time"
+
+	"github.com/golang/glog"
+
+	"skia.googlesource.com/buildbot.git/go/gitinfo"
+)
+
+/*
+	Utilities for caching commit data.
+*/
+
+// CommitCache is a struct used for caching commit data. Stores ALL commits in
+// the repository.
+type CommitCache struct {
+	branchHeads []*gitinfo.GitBranch
+	commits     []*gitinfo.LongCommit
+	repo        *gitinfo.GitInfo
+	mutex       sync.RWMutex
+}
+
+// New creates and returns a new CommitCache which watches the given repo.
+// The initial Update will load ALL commits from the repository, so expect
+// this to be slow.
+func New(repo *gitinfo.GitInfo) (*CommitCache, error) {
+	// Initially load the past week's worth of commits.
+	c := CommitCache{
+		repo: repo,
+	}
+	if err := c.Update(); err != nil {
+		return nil, err
+	}
+	return &c, nil
+}
+
+// Update syncs the source code repository and loads any new commits.
+func (c *CommitCache) Update() error {
+	glog.Info("Reloading commits.")
+	c.mutex.Lock()
+	defer c.mutex.Unlock()
+	if err := c.repo.Update(true, true); err != nil {
+		return fmt.Errorf("Failed to update the repo: %v", err)
+	}
+	from := time.Time{}
+	if len(c.commits) > 0 {
+		from = c.commits[len(c.commits)-1].Timestamp
+	}
+	newCommitHashes := c.repo.From(from)
+	glog.Infof("Processing %d new commits.", len(newCommitHashes))
+	newCommits := make([]*gitinfo.LongCommit, len(newCommitHashes))
+	if len(newCommitHashes) > 0 {
+		for i, h := range newCommitHashes {
+			d, err := c.repo.Details(h)
+			if err != nil {
+				return fmt.Errorf("Failed to obtain commit details for %s: %v", h, err)
+			}
+			newCommits[i] = d
+		}
+	}
+	branchHeads, err := c.repo.GetBranches()
+	if err != nil {
+		return fmt.Errorf("Failed to read branch information from the repo: %v", err)
+	}
+	// Update the cached values all at once at at the end.
+	c.branchHeads = branchHeads
+	c.commits = append(c.commits, newCommits...)
+	return nil
+}
+
+// NumCommits returns the number of commits contained in the cache.
+func (c *CommitCache) NumCommits() int {
+	return len(c.commits)
+}
+
+// asJson writes the given commit range along with the branch heads in JSON
+// format to the given Writer.
+func (c *CommitCache) asJson(w io.Writer, startIdx, endIdx int) error {
+	c.mutex.RLock()
+	defer c.mutex.RUnlock()
+	data := struct {
+		Commits     []*gitinfo.LongCommit `json:"commits"`
+		BranchHeads []*gitinfo.GitBranch  `json:"branch_heads"`
+		StartIdx    int                   `json:"startIdx"`
+		EndIdx      int                   `json:"endIdx"`
+	}{
+		Commits:     c.commits[startIdx:endIdx],
+		BranchHeads: c.branchHeads,
+		StartIdx:    startIdx,
+		EndIdx:      endIdx,
+	}
+	return json.NewEncoder(w).Encode(&data)
+}
+
+// LastNAsJson writes the last N commits along with the branch heads in JSON
+// format to the given Writer.
+func (c *CommitCache) LastNAsJson(w io.Writer, n int) error {
+	c.mutex.RLock()
+	end := len(c.commits)
+	c.mutex.RUnlock()
+	start := end - n
+	if start < 0 {
+		start = 0
+	}
+	return c.asJson(w, start, end)
+}
+
+// RangeAsJson writes the given range of commits along with the branch heads
+// in JSON format to the given Writer.
+func (c *CommitCache) RangeAsJson(w io.Writer, startIdx, endIdx int) error {
+	if startIdx < 0 || startIdx > len(c.commits) {
+		return fmt.Errorf("startIdx is out of range [0, %d]: %d", len(c.commits), startIdx)
+	}
+	if endIdx < 0 || endIdx > len(c.commits) {
+		return fmt.Errorf("endIdx is out of range [0, %d]: %d", len(c.commits), endIdx)
+	}
+	if endIdx < startIdx {
+		return fmt.Errorf("endIdx < startIdx: %d, %d", endIdx, startIdx)
+	}
+	return c.asJson(w, startIdx, endIdx)
+}
diff --git a/monitoring/res/imp/commits-sk.html b/monitoring/res/imp/commits-sk.html
index 3d2262b..337832d 100644
--- a/monitoring/res/imp/commits-sk.html
+++ b/monitoring/res/imp/commits-sk.html
@@ -38,6 +38,10 @@
     a {
       color: inherit;
     }
+    #moreButton {
+      width: 40px;
+      height: 40px;
+    }
     </style>
     <div vertical layout flex>
       <div horizontal layout center id="loadstatus">
@@ -55,7 +59,7 @@
           <table class="commitList">
             <template repeat="{{commit in commits}}">
               <tr class="commit" style="color: {{getCommitColor(displayCommits[commit.hash])}}">
-                <td><a href="https://skia.googlesource.com/skiabot-test/+/{{commit.hash}}" target="_blank">{{commit.hash|shortCommit}}</a></td>
+                <td><a href="https://skia.googlesource.com/skia/+/{{commit.hash}}" target="_blank">{{commit.hash|shortCommit}}</a></td>
                 <td>{{commit.author|shortAuthor}}</td>
                 <td>{{commit.subject|shortSubject}}</td>
               </tr>
@@ -63,15 +67,18 @@
           </table>
         </div>
       </div>
+      <!-- TODO(borenet): Automatically loadMore when the user scrolls to the bottom? -->
+      <core-icon-button id="moreButton" icon="add" on-click="{{loadMore}}"></core-icon-button>
     </div>
   </template>
   <script>
   (function() {
-    var commitY = 20;          // Vertical pixels used by each commit.
-    var paddingX = 10;         // Left-side padding pixels.
-    var paddingY = 20;         // Top padding pixels.
-    var radius = 3;            // Radius of commit dots.
-    var columnWidth = commitY; // Pixel width of per-branch colums.
+    var defaultCommitsToLoad = 35; // Default number of commits to load.
+    var commitY = 20;              // Vertical pixels used by each commit.
+    var paddingX = 10;             // Left-side padding pixels.
+    var paddingY = 20;             // Top padding pixels.
+    var radius = 3;                // Radius of commit dots.
+    var columnWidth = commitY;     // Pixel width of per-branch colums.
     // Colors used for the branches. Obtained from
     // http://blog.mollietaylor.com/2012/10/color-blindness-and-palette-choice.html
     var palette = [
@@ -282,7 +289,12 @@
       for (var b = 0; b < branches.length; b++) {
         // Add a label to commits at branch heads.
         var hash = branches[b].head
-        displayCommits[branches[b].head].label.push(branches[b].name);
+        // The branch might have scrolled out of the time window. If so, just
+        // skip it.
+        if (!displayCommits[hash]) {
+          continue
+        }
+        displayCommits[hash].label.push(branches[b].name);
         if (traceCommits(displayCommits, commits, remaining, hash, column)) {
           column++;
         }
@@ -308,7 +320,7 @@
           value: null,
           reflect: true,
         },
-        dispayCommits: {
+        displayCommits: {
           value: null,
           reflect: true,
         },
@@ -329,10 +341,12 @@
       created: function() {
         this.commits = [];
         this.branchHeads = [];
+        this.startIdx = null;
+        this.endIdx = null;
         this.reloadCommits();
         var that = this;
         window.addEventListener("resize", function() {
-          that.draw();
+          that.draw(that.commits, that.branchHeads);
         }, true);
       },
 
@@ -376,28 +390,98 @@
         }
         if (this.reload > 0) {
           var that = this;
-          this.timeout = window.setTimeout(function() { that.reloadCommits(); }, this.reload * 1000);
+          this.timeout = window.setTimeout(function() {
+            that.reloadCommits(that.endIdx);
+          }, this.reload * 1000);
         }
       },
 
-      reloadCommits: function() {
+      loadMore: function() {
+        this.reloadCommits(this.startIdx - defaultCommitsToLoad, this.startIdx);
+      },
+
+      // Reload the commits. If the startIdx and endIdx parameters are given,
+      // loads the commits in that range. If not, load the most recent N
+      // commits, where N is the default number returned by the server.
+      reloadCommits: function(startIdx, endIdx) {
         console.log("Loading commits.");
+        if (this.$) {
+          this.$.moreButton.disabled = true;
+        }
+        var url = "/json/commits";
+	if (startIdx) {
+          url += "?start=" + startIdx;
+          if (endIdx) {
+            url += "&end=" + endIdx;
+          }
+        }
+        console.log("GET " + url);
         var that = this;
-        sk.get("/json/commits").then(JSON.parse).then(function(json) {
-          that.commits = json.commits;
-          that.commits.reverse();
-          that.branchHeads = json.branch_heads;
-          that.lastLoaded = new Date().toLocaleTimeString();
-          that.resetTimeout();
-          console.log("Done loading commits.");
-          that.draw();
+        sk.get(url).then(JSON.parse).then(function(json) {
+          try {
+            json.commits.reverse();
+            that.lastLoaded = new Date().toLocaleTimeString();
+
+            // Merge the new commits into the existing set.
+            // Ensure that the new commits line up exactly with the existing ones.
+            if (json.endIdx - json.startIdx != json.commits.length) {
+              console.error("Server returned invalid number of commits.");
+              return;
+            }
+            var commits = null;
+            // Case 1: Loading initial set of commits.
+            if (!that.startIdx || !that.endIdx) {
+              commits = json.commits;
+              that.startIdx = json.startIdx;
+              that.endIdx = json.endIdx;
+            }
+            // Case 2: Loading earlier commits.
+            else if (json.startIdx < that.startIdx) {
+              if (json.endIdx != that.startIdx) {
+                console.error("Server returned invalid set of commits.");
+                return;
+              }
+              commits = that.commits.concat(json.commits);
+              that.startIdx = json.startIdx;
+            }
+            // Case 3: Loading newer commits.
+            else if (json.endIdx >= that.endIdx) {
+              if (json.startIdx != that.endIdx) {
+                console.error("Server returned invalid set of commits.");
+                return;
+              }
+              if (json.commits.length == 0) {
+                console.log("No new commits. Skipping draw.");
+                return;
+              }
+              commits = json.commits.concat(that.commits);
+              that.endIdx = json.endIdx;
+            }
+            // ???
+            else {
+              console.error("Server returned invalid data.");
+              return;
+            }
+            // Actually draw the commits.
+            that.draw(commits, json.branch_heads);
+            that.commits = commits;
+            that.branchHeads = json.branch_heads;
+          } catch(e) {
+            console.error(e.stack);
+            return;
+          } finally {
+            that.resetTimeout();
+            if (that.$) {
+              that.$.moreButton.disabled = false;
+            }
+          }
         });
       },
 
-      draw: function() {
+      draw: function(commits, branchHeads) {
         console.log("Drawing.");
         // Initialize all commits.
-        var prep = prepareCommitsForDisplay(this.commits, this.branchHeads);
+        var prep = prepareCommitsForDisplay(commits, branchHeads);
         this.displayCommits = prep[0];
         var numColumns = prep[1];
 
@@ -408,8 +492,8 @@
         var dummyCtx = document.createElement("canvas").getContext("2d");
         dummyCtx.font = font;
         var longestWidth = 0;
-        for (var i = 0; i < this.commits.length; i++) {
-          var c = this.displayCommits[this.commits[i].hash];
+        for (var i = 0; i < commits.length; i++) {
+          var c = this.displayCommits[commits[i].hash];
           var w = c.labelWidth(dummyCtx);
           w += commitY * (c.column + 1);
           if (w > longestWidth) {
@@ -422,7 +506,7 @@
         var parent = this.shadowRoot.getElementById("canvasContainer");
         var canvas = this.shadowRoot.getElementById("commitCanvas");
         var w = longestWidth + paddingX;
-        var h = commitY * this.commits.length;
+        var h = commitY * commits.length;
         canvas.style.width = w + "px";
         canvas.style.height = h + "px";
         canvas.width = w * scale;
@@ -433,13 +517,13 @@
         ctx.font = font;
 
         // Shade an alternating background.
-        for (var i = 0; i < this.commits.length; i++) {
-          this.displayCommits[this.commits[i].hash].drawBackground(ctx);
+        for (var i = 0; i < commits.length; i++) {
+          this.displayCommits[commits[i].hash].drawBackground(ctx);
         }
 
         // Draw the commits.
-        for (var i = 0; i < this.commits.length; i++) {
-          this.displayCommits[this.commits[i].hash].draw(ctx, this.displayCommits);
+        for (var i = 0; i < commits.length; i++) {
+          this.displayCommits[commits[i].hash].draw(ctx, this.displayCommits);
         }
       },
     });