6321: Add OSError to slurm shutdown actor retry conditions, to catch and retry

[arvados.git] / services / keepstore / azure_blob_volume.go

diff --git a/services/keepstore/azure_blob_volume.go b/services/keepstore/azure_blob_volume.go
index 79123a9747e2aa32d2cb986dab0570af87118ae6..657c3151caade8aeca6cbedcd96ffef70d3d7ac4 100644 (file)
--- a/services/keepstore/azure_blob_volume.go
+++ b/services/keepstore/azure_blob_volume.go
@@ -19,6 +19,8 @@ var (
        azureStorageAccountName    string
        azureStorageAccountKeyFile string
        azureStorageReplication    int
+       azureWriteRaceInterval     time.Duration = 15 * time.Second
+       azureWriteRacePollTime     time.Duration = time.Second
 )
 
 func readKeyFromFile(file string) (string, error) {
@@ -117,25 +119,49 @@ func (v *AzureBlobVolume) Check() error {
 }
 
 func (v *AzureBlobVolume) Get(loc string) ([]byte, error) {
-       rdr, err := v.bsClient.GetBlob(v.containerName, loc)
-       if err != nil {
-               if strings.Contains(err.Error(), "404 Not Found") {
-                       // "storage: service returned without a response body (404 Not Found)"
-                       return nil, os.ErrNotExist
+       var deadline time.Time
+       haveDeadline := false
+       buf, err := v.get(loc)
+       for err == nil && len(buf) == 0 && loc != "d41d8cd98f00b204e9800998ecf8427e" {
+               // Seeing a brand new empty block probably means we're
+               // in a race with CreateBlob, which under the hood
+               // (apparently) does "CreateEmpty" and "CommitData"
+               // with no additional transaction locking.
+               if !haveDeadline {
+                       t, err := v.Mtime(loc)
+                       if err != nil {
+                               log.Print("Got empty block (possible race) but Mtime failed: ", err)
+                               break
+                       }
+                       deadline = t.Add(azureWriteRaceInterval)
+                       if time.Now().After(deadline) {
+                               break
+                       }
+                       log.Printf("Race? Block %s is 0 bytes, %s old. Polling until %s", loc, time.Since(t), deadline)
+                       haveDeadline = true
+               } else if time.Now().After(deadline) {
+                       break
                }
-               return nil, err
+               bufs.Put(buf)
+               time.Sleep(azureWriteRacePollTime)
+               buf, err = v.get(loc)
        }
-       switch err := err.(type) {
-       case nil:
-       default:
-               log.Printf("ERROR IN Get(): %T %#v", err, err)
-               return nil, err
+       if haveDeadline {
+               log.Printf("Race ended with len(buf)==%d", len(buf))
+       }
+       return buf, err
+}
+
+func (v *AzureBlobVolume) get(loc string) ([]byte, error) {
+       rdr, err := v.bsClient.GetBlob(v.containerName, loc)
+       if err != nil {
+               return nil, v.translateError(err)
        }
        defer rdr.Close()
        buf := bufs.Get(BlockSize)
        n, err := io.ReadFull(rdr, buf)
        switch err {
-       case io.EOF, io.ErrUnexpectedEOF:
+       case nil, io.EOF, io.ErrUnexpectedEOF:
                return buf[:n], nil
        default:
                bufs.Put(buf)
@@ -146,7 +172,7 @@ func (v *AzureBlobVolume) Get(loc string) ([]byte, error) {
 func (v *AzureBlobVolume) Compare(loc string, expect []byte) error {
        rdr, err := v.bsClient.GetBlob(v.containerName, loc)
        if err != nil {
-               return err
+               return v.translateError(err)
        }
        defer rdr.Close()
        return compareReaderWithBuf(rdr, expect, loc[:32])
@@ -190,6 +216,14 @@ func (v *AzureBlobVolume) IndexTo(prefix string, writer io.Writer) error {
                        if err != nil {
                                return err
                        }
+                       if b.Properties.ContentLength == 0 && t.Add(azureWriteRaceInterval).After(time.Now()) {
+                               // A new zero-length blob is probably
+                               // just a new non-empty blob that
+                               // hasn't committed its data yet (see
+                               // Get()), and in any case has no
+                               // value.
+                               continue
+                       }
                        fmt.Fprintf(writer, "%s+%d %d\n", b.Name, b.Properties.ContentLength, t.Unix())
                }
                if resp.NextMarker == "" {
@@ -241,3 +275,17 @@ func (v *AzureBlobVolume) Writable() bool {
 func (v *AzureBlobVolume) Replication() int {
        return v.replication
 }
+
+// If possible, translate an Azure SDK error to a recognizable error
+// like os.ErrNotExist.
+func (v *AzureBlobVolume) translateError(err error) error {
+       switch {
+       case err == nil:
+               return err
+       case strings.Contains(err.Error(), "404 Not Found"):
+               // "storage: service returned without a response body (404 Not Found)"
+               return os.ErrNotExist
+       default:
+               return err
+       }
+}