[jira] [Created] (OAK-7339) Fix all sidegrades breaking with UnsupportedOperationException on MissingBlobStore by introducing LoopbackBlobStore

["Arek Kita (JIRA)" <ji...@apache.org>]

Arek Kita created OAK-7339:
------------------------------

             Summary: Fix all sidegrades breaking with UnsupportedOperationException on MissingBlobStore by introducing LoopbackBlobStore
                 Key: OAK-7339
                 URL: https://issues.apache.org/jira/browse/OAK-7339
             Project: Jackrabbit Oak
          Issue Type: Bug
          Components: upgrade
    Affects Versions: 1.8.0, 1.6.0
            Reporter: Arek Kita
            Assignee: Arek Kita
             Fix For: 1.9.0


h4. Problem

In some edge cases when the binary under the same path (/content/asset1) is modified by 2 independent checkpoints: A & B the sidegrade without providing DataStore might fail with the following error:

{noformat:title=An exception thrown by oak-upgrade tool}
Caused by: java.lang.UnsupportedOperationException: null
    at org.apache.jackrabbit.oak.upgrade.cli.blob.MissingBlobStore.getInputStream(MissingBlobStore.java:62)
    at org.apache.jackrabbit.oak.plugins.blob.BlobStoreBlob.getNewStream(BlobStoreBlob.java:47)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentBlob.getNewStream(SegmentBlob.java:276)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentBlob.getNewStream(SegmentBlob.java:86)
    at org.apache.jackrabbit.oak.plugins.memory.AbstractBlob$1.openStream(AbstractBlob.java:44)
    at com.google.common.io.ByteSource.contentEquals(ByteSource.java:344)
    at org.apache.jackrabbit.oak.plugins.memory.AbstractBlob.equal(AbstractBlob.java:67)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentBlob.equals(SegmentBlob.java:227)
    at com.google.common.base.Objects.equal(Objects.java:60)
    at org.apache.jackrabbit.oak.plugins.memory.AbstractPropertyState.equal(AbstractPropertyState.java:59)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentPropertyState.equals(SegmentPropertyState.java:242)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentNodeState.compareProperties(SegmentNodeState.java:617)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentNodeState.compareAgainstBaseState(SegmentNodeState.java:511)
(the same nested methods)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentNodeState.compareAgainstBaseState(SegmentNodeState.java:604)
    at org.apache.jackrabbit.oak.upgrade.PersistingDiff.diff(PersistingDiff.java:139)
    at org.apache.jackrabbit.oak.upgrade.PersistingDiff.childNodeChanged(PersistingDiff.java:191)
    at org.apache.jackrabbit.oak.plugins.segment.MapRecord$3.childNodeChanged(MapRecord.java:440)
    at org.apache.jackrabbit.oak.plugins.segment.MapRecord.compare(MapRecord.java:483)
    at org.apache.jackrabbit.oak.plugins.segment.MapRecord.compare(MapRecord.java:432)
    at org.apache.jackrabbit.oak.plugins.segment.SegmentNodeState.compareAgainstBaseState(SegmentNodeState.java:604)
    at org.apache.jackrabbit.oak.upgrade.PersistingDiff.diff(PersistingDiff.java:139)
    at org.apache.jackrabbit.oak.upgrade.PersistingDiff.applyDiffOnNodeState(PersistingDiff.java:106)
    at org.apache.jackrabbit.oak.upgrade.RepositorySidegrade.copyDiffToTarget(RepositorySidegrade.java:403)
    at org.apache.jackrabbit.oak.upgrade.RepositorySidegrade.migrateWithCheckpoints(RepositorySidegrade.java:347)
{noformat}

 

h4. Abstract of proposed solution

The idea for migration is simple: instead of failing on:
{code:java}public InputStream getInputStream(String blobId) throws IOException;
{code}
or
{code:java}public int readBlob(String blobId, long pos, byte[] buff, int off, int length) throws IOException;
{code}
lets introduce a BlobStore implementation that acts similarly as a *localhost* interface that what you sent it will resend back to this interface.
h4. How it works

It works as a *localhost* interface, the same way: when *{{blobId}}* is requested... then *{{blobId}}* is served as a binary content instead *of throwing*: {{UnsupportedOperationException}}.

This allows to act quickly on migrations that requires to compare binaries in order to satisfy requirements for checkpoints to be rewritten, copied from scratch.
h4. Pros
 * simplifies simple sidegrade migration use cases: you do not need anymore to include your DataStore (which slows that migration not necessary) on the command line when the migration is failing
 * speeds up the migration as it doesn't require to reference BlobStore implementation in cases where binary references are only copied together with NodeStore inlined binaries
 * you're always copying checkpoints which means (no need anymore for {{--skip-checkpoints}} option) that no full re-indexes are happening anymore after migration on migrated repository

h4. Cons
 * not visible effect to user that for a specific migration a DataStore is needed (whether you are running into this specific edge case)



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