func (sis SegmentInfos) SegmentsFileName() string {
return util.FileNameFromGeneration(util.SEGMENTS, "", sis.lastGeneration)
}
// TODO support IndexCommit
func (fsf *FindSegmentsFile) run() (obj interface{}, err error) {
log.Print("Finding segments file...")
// if commit != nil {
// if fsf.directory != commit.Directory {
// return nil, errors.New("the specified commit does not match the specified Directory")
// }
// return fsf.doBody(commit.SegmentsFileName)
// }
lastGen := int64(-1)
gen := int64(0)
genLookaheadCount := 0
var exc error
retryCount := 0
useFirstMethod := true
// Loop until we succeed in calling doBody() without
// hitting an IOException. An IOException most likely
// means a commit was in process and has finished, in
// the time it took us to load the now-old infos files
// (and segments files). It's also possible it's a
// true error (corrupt index). To distinguish these,
// on each retry we must see "forward progress" on
// which generation we are trying to load. If we
// don't, then the original error is real and we throw
// it.
// We have three methods for determining the current
// generation. We try the first two in parallel (when
// useFirstMethod is true), and fall back to the third
// when necessary.
for {
log.Print("Trying...")
if useFirstMethod {
log.Print("Trying first method...")
// List the directory and use the highest
// segments_N file. This method works well as long
// as there is no stale caching on the directory
// contents (NOTE: NFS clients often have such stale
// caching):
genA := int64(-1)
files, err := fsf.directory.ListAll()
if err != nil {
return nil, err
}
if files != nil {
genA = LastCommitGeneration(files)
}
// TODO support info stream
// if fsf.infoStream != nil {
// message("directory listing genA=" + genA)
// }
log.Printf("directory listing genA=%v", genA)
// Also open segments.gen and read its
// contents. Then we take the larger of the two
// gens. This way, if either approach is hitting
// a stale cache (NFS) we have a better chance of
// getting the right generation.
genB := int64(-1)
genInput, err := fsf.directory.OpenInput(INDEX_FILENAME_SEGMENTS_GEN, store.IO_CONTEXT_READ)
if err != nil {
// if fsf.infoStream != nil {
log.Printf("segments.gen open: %v", err)
// }
} else {
defer genInput.Close()
log.Print("Reading segments info...")
version, err := genInput.ReadInt()
if err != nil {
return nil, err
}
log.Printf("Version: %v", version)
if version == FORMAT_SEGMENTS_GEN_CURRENT {
log.Print("Version is current.")
gen0, err := genInput.ReadLong()
if err != nil {
return nil, err
}
gen1, err := genInput.ReadLong()
if err != nil {
return nil, err
} else {
// if fsf.infoStream != nil {
log.Printf("fallback check: %v; %v", gen0, gen1)
// }
if gen0 == gen1 {
// The file is consistent.
genB = gen0
}
}
} else {
return nil, codec.NewIndexFormatTooNewError(genInput, version, FORMAT_SEGMENTS_GEN_CURRENT, FORMAT_SEGMENTS_GEN_CURRENT)
}
}
// if fsf.infoStream != nil {
log.Printf("%v check: genB=%v", INDEX_FILENAME_SEGMENTS_GEN, genB)
// }
// Pick the larger of the two gen's:
gen = genA
if genB > gen {
gen = genB
}
if gen == -1 {
// Neither approach found a generation
return nil, errors.New(fmt.Sprintf("no segments* file found in %v: files: %#v", fsf.directory, files))
}
}
if useFirstMethod && lastGen == gen && retryCount >= 2 {
// Give up on first method -- this is 3rd cycle on
// listing directory and checking gen file to
// attempt to locate the segments file.
useFirstMethod = false
}
// Second method: since both directory cache and
// file contents cache seem to be stale, just
// advance the generation.
if !useFirstMethod {
if genLookaheadCount < fsf.defaultGenLookaheadCount {
gen++
genLookaheadCount++
// if fsf.infoStream != nil {
log.Printf("look ahead increment gen to %v", gen)
// }
} else {
// All attempts have failed -- throw first exc:
return nil, exc
}
} else if lastGen == gen {
// This means we're about to try the same
// segments_N last tried.
retryCount++
} else {
// Segment file has advanced since our last loop
// (we made "progress"), so reset retryCount:
retryCount = 0
}
lastGen = gen
segmentFileName := util.FileNameFromGeneration(INDEX_FILENAME_SEGMENTS, "", gen)
log.Printf("SegmentFileName: %v", segmentFileName)
v, err := fsf.doBody(segmentFileName)
if err != nil {
// Save the original root cause:
if exc == nil {
exc = err
}
// if fsf.infoStream != nil {
log.Printf("primary Exception on '%v': %v; will retry: retryCount = %v; gen = %v",
segmentFileName, err, retryCount, gen)
// }
if gen > 1 && useFirstMethod && retryCount == 1 {
// This is our second time trying this same segments
// file (because retryCount is 1), and, there is
// possibly a segments_(N-1) (because gen > 1).
// So, check if the segments_(N-1) exists and
// try it if so:
prevSegmentFileName := util.FileNameFromGeneration(INDEX_FILENAME_SEGMENTS, "", gen-1)
if prevExists := fsf.directory.FileExists(prevSegmentFileName); prevExists {
// if fsf.infoStream != nil {
log.Printf("fallback to prior segment file '%v'", prevSegmentFileName)
// }
v, err = fsf.doBody(prevSegmentFileName)
if err != nil {
// if fsf.infoStream != nil {
log.Printf("secondary Exception on '%v': %v; will retry", prevSegmentFileName, err)
//}
} else {
// if fsf.infoStream != nil {
log.Printf("success on fallback %v", prevSegmentFileName)
//}
return v, nil
}
}
}
} else {
// if fsf.infoStream != nil {
log.Printf("success on %v", segmentFileName)
// }
return v, nil
}
}
}
