Github user li-zhihui commented on a diff in the pull request:
https://github.com/apache/spark/pull/1616#discussion_r17578863
--- Diff: core/src/main/scala/org/apache/spark/util/Utils.scala ---
@@ -313,15 +313,84 @@ private[spark] object Utils extends Logging {
}
/**
+ * Download a file requested by the executor . Supports fetching the
file in a variety of ways,
+ * including HTTP, HDFS and files on a standard filesystem, based on the
URL parameter.
+ *
+ * If `useCache` is true, first attempts to fetch the file from a local
cache that's shared across
+ * executors running the same application.
+ *
+ * Throws SparkException if the target file already exists and has
different contents than
+ * the requested file.
+ */
+ def fetchFile(
+ url: String,
+ targetDir: File,
+ conf: SparkConf,
+ securityMgr: SecurityManager,
+ hadoopConf: Configuration,
+ timestamp: Long,
+ useCache: Boolean) {
+ val fileName = url.split("/").last
+ val targetFile = new File(targetDir, fileName)
+ if (useCache) {
+ val cachedFileName = s"${url.hashCode}${timestamp}_cache"
+ val lockFileName = s"${url.hashCode}${timestamp}_lock"
+ val localDir = new File(getLocalDir(conf))
+ val lockFile = new File(localDir, lockFileName)
+ val raf = new RandomAccessFile(lockFile, "rw")
+ // Only one executor entry.
+ // The FileLock is only used to control synchronization for
executors download file,
+ // it's always safe regardless of lock type(mandatory or advisory).
+ val lock = raf.getChannel().lock()
+ val cachedFile = new File(localDir, cachedFileName)
+ try {
+ if (!cachedFile.exists()) {
+ doFetchFile(url, localDir, cachedFileName, conf, securityMgr,
hadoopConf)
+ }
+ } finally {
+ lock.release()
+ }
+ if (targetFile.exists && !Files.equal(cachedFile, targetFile)) {
--- End diff --
This PR try to avoid network blocking (multiple executors download file by
network to local storage only once). So each executor still fetch files to
their work directory, but only from local storage ,not from remote node by
network.
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