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https://issues.apache.org/jira/browse/HADOOP-14457?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16057360#comment-16057360
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Steve Loughran commented on HADOOP-14457:
-----------------------------------------
This is becoming an intersting little architectural issue
* I concur with the "auto-create parent dirs is bad" opinion; In the evolving
builder API for new files, HADOOP-14365, I want it to *not* create parent dirs,
so users of the new API can call mkdir first if they really want it.
* we should consider whether {{createNonRecursive()}} is actually lined up
right here, or whether it needs changes too. (And tests; created HADOOP-14562
there).
* we need to have an efficient codepath for the mkdirs/create sequence. One
thing to consider here: if done correctly, in auth mode, the existence of a
parent is sufficient to guarantee the existence of all its parents. Therefore
you will only need to go up the tree for all nonexistent parents.
* ...and line up for that builder. So maybe the core inner create operation
would take flags indicating parent dir policy, if create: walk up creating
parents. If not: fail fast if parent != dir.
* As noted, multiple round trips are bad...not just in perf but in billable
IOPs.
* and w.r.t capability checks, static interface capabilities cause problems in
subclasses, witness {{Syncable}}. Some dynamic probe is the only solution agile
enough to cope, IMO.
So: how about we optimise for the create-parent-must-exist and
create-parent-probably-exists use cases, and treat the other one (no parent
tree) as an outlier we can make expensive?
> create() does not notify metadataStore of parent directories or ensure
> they're not existing files
> -------------------------------------------------------------------------------------------------
>
> Key: HADOOP-14457
> URL: https://issues.apache.org/jira/browse/HADOOP-14457
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: fs/s3
> Reporter: Sean Mackrory
> Assignee: Sean Mackrory
> Attachments: HADOOP-14457-HADOOP-13345.001.patch,
> HADOOP-14457-HADOOP-13345.002.patch, HADOOP-14457-HADOOP-13345.003.patch,
> HADOOP-14457-HADOOP-13345.004.patch, HADOOP-14457-HADOOP-13345.005.patch,
> HADOOP-14457-HADOOP-13345.006.patch, HADOOP-14457-HADOOP-13345.007.patch,
> HADOOP-14457-HADOOP-13345.008.patch, HADOOP-14457-HADOOP-13345.009.patch
>
>
> Not a great test yet, but it at least reliably demonstrates the issue.
> LocalMetadataStore will sometimes erroneously report that a directory is
> empty with isAuthoritative = true when it *definitely* has children the
> metadatastore should know about. It doesn't appear to happen if the children
> are just directory. The fact that it's returning an empty listing is
> concerning, but the fact that it says it's authoritative *might* be a second
> bug.
> {code}
> diff --git
> a/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java
>
> b/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java
> index 78b3970..1821d19 100644
> ---
> a/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java
> +++
> b/hadoop-tools/hadoop-aws/src/main/java/org/apache/hadoop/fs/s3a/S3AFileSystem.java
> @@ -965,7 +965,7 @@ public boolean hasMetadataStore() {
> }
>
> @VisibleForTesting
> - MetadataStore getMetadataStore() {
> + public MetadataStore getMetadataStore() {
> return metadataStore;
> }
>
> diff --git
> a/hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/contract/s3a/ITestS3AContractRename.java
>
> b/hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/contract/s3a/ITestS3AContractRename.java
> index 4339649..881bdc9 100644
> ---
> a/hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/contract/s3a/ITestS3AContractRename.java
> +++
> b/hadoop-tools/hadoop-aws/src/test/java/org/apache/hadoop/fs/contract/s3a/ITestS3AContractRename.java
> @@ -23,6 +23,11 @@
> import org.apache.hadoop.fs.contract.AbstractFSContract;
> import org.apache.hadoop.fs.FileSystem;
> import org.apache.hadoop.fs.Path;
> +import org.apache.hadoop.fs.s3a.S3AFileSystem;
> +import org.apache.hadoop.fs.s3a.Tristate;
> +import org.apache.hadoop.fs.s3a.s3guard.DirListingMetadata;
> +import org.apache.hadoop.fs.s3a.s3guard.MetadataStore;
> +import org.junit.Test;
>
> import static org.apache.hadoop.fs.contract.ContractTestUtils.dataset;
> import static org.apache.hadoop.fs.contract.ContractTestUtils.writeDataset;
> @@ -72,4 +77,24 @@ public void testRenameDirIntoExistingDir() throws
> Throwable {
> boolean rename = fs.rename(srcDir, destDir);
> assertFalse("s3a doesn't support rename to non-empty directory", rename);
> }
> +
> + @Test
> + public void testMkdirPopulatesFileAncestors() throws Exception {
> + final FileSystem fs = getFileSystem();
> + final MetadataStore ms = ((S3AFileSystem) fs).getMetadataStore();
> + final Path parent = path("testMkdirPopulatesFileAncestors/source");
> + try {
> + fs.mkdirs(parent);
> + final Path nestedFile = new Path(parent, "dir1/dir2/dir3/file4");
> + byte[] srcDataset = dataset(256, 'a', 'z');
> + writeDataset(fs, nestedFile, srcDataset, srcDataset.length,
> + 1024, false);
> +
> + DirListingMetadata list = ms.listChildren(parent);
> + assertTrue("MetadataStore falsely reports authoritative empty list",
> + list.isEmpty() == Tristate.FALSE || !list.isAuthoritative());
> + } finally {
> + fs.delete(parent, true);
> + }
> + }
> }
> {code}
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