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| <div class="subTitle">org.apache.beam.sdk.io.gcp.bigtable.changestreams.reconciler</div> |
| <h2 title="Class PartitionReconciler" class="title">Class PartitionReconciler</h2> |
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| <li>java.lang.Object</li> |
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| <li>org.apache.beam.sdk.io.gcp.bigtable.changestreams.reconciler.PartitionReconciler</li> |
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| <pre><a href="../../../../../../../../../org/apache/beam/sdk/annotations/Internal.html" title="annotation in org.apache.beam.sdk.annotations">@Internal</a> |
| public class <span class="typeNameLabel">PartitionReconciler</span> |
| extends java.lang.Object</pre> |
| <div class="block">There can be a race when many splits and merges happen to a single partition in quick succession. |
| It's possible that some CloseStream merge messages may be missed. This can lead to an |
| inconsistent state in the metadata table causing some partitions to not be streamed at all. This |
| class tries to reconcile the problem by ensuring that all partitions are streamed. If any |
| partitions are missing for an extended period of time, we fix it by creating a new |
| partitionRecord to stream the partition. |
| |
| <p>Example of race condition: |
| |
| <ol> |
| <li>Bigtable: decides to merge A-B and B-C to A-C |
| <li>Beam A-B: receives CloseStream to merge into Partition A-C . Creates entry in metadata and |
| terminates the stream. |
| <li>Beam B-C: is not currently streaming because it just check pointed and hasn't restarted |
| yet. |
| <li>Bigtable: decides maybe merge wasn't good, splits A-C back into A-B and B-C |
| <li>Beam B-C: restarts now, but it never receives the 1st CloseStream merge message and it |
| never will because CloseStream messages are not queued and because when requesting Change |
| Stream for B-C, Bigtable recognizes that B-C does exist, so it's happy to start the stream. |
| <li>Beam A-B: doesn't exist... it's in the metadata table waiting for B-C to merge into A-C. |
| </ol> |
| |
| <p>To reconcile this, we identify partitions that haven't been streamed for at least 5 minutes. |
| This is probably an indication that there were some races of CloseStream merge messages.</div> |
| </li> |
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| <td class="colOne"><code><span class="memberNameLink"><a href="../../../../../../../../../org/apache/beam/sdk/io/gcp/bigtable/changestreams/reconciler/PartitionReconciler.html#PartitionReconciler-org.apache.beam.sdk.io.gcp.bigtable.changestreams.dao.MetadataTableDao-">PartitionReconciler</a></span>(<a href="../../../../../../../../../org/apache/beam/sdk/io/gcp/bigtable/changestreams/dao/MetadataTableDao.html" title="class in org.apache.beam.sdk.io.gcp.bigtable.changestreams.dao">MetadataTableDao</a> metadataTableDao)</code> </td> |
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| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../../org/apache/beam/sdk/io/gcp/bigtable/changestreams/reconciler/PartitionReconciler.html#addMissingPartitions-java.util.List-">addMissingPartitions</a></span>(java.util.List<com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange> missingPartitions)</code> |
| <div class="block">Capture partitions that are not currently being streamed.</div> |
| </td> |
| </tr> |
| <tr id="i1" class="rowColor"> |
| <td class="colFirst"><code>void</code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../../org/apache/beam/sdk/io/gcp/bigtable/changestreams/reconciler/PartitionReconciler.html#addNewPartition-com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange-com.google.protobuf.ByteString-">addNewPartition</a></span>(com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange partition, |
| com.google.protobuf.ByteString rowKey)</code> |
| <div class="block">Capture NewPartition row that's waiting to be created.</div> |
| </td> |
| </tr> |
| <tr id="i2" class="altColor"> |
| <td class="colFirst"><code>java.util.HashMap<com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange,java.util.Set<com.google.protobuf.ByteString>></code></td> |
| <td class="colLast"><code><span class="memberNameLink"><a href="../../../../../../../../../org/apache/beam/sdk/io/gcp/bigtable/changestreams/reconciler/PartitionReconciler.html#getPartitionsToReconcile--">getPartitionsToReconcile</a></span>()</code> |
| <div class="block">Match partitions that have been missing for a while and need to be reconciled with NewPartition |
| row key.</div> |
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| <h4>PartitionReconciler</h4> |
| <pre>public PartitionReconciler(<a href="../../../../../../../../../org/apache/beam/sdk/io/gcp/bigtable/changestreams/dao/MetadataTableDao.html" title="class in org.apache.beam.sdk.io.gcp.bigtable.changestreams.dao">MetadataTableDao</a> metadataTableDao)</pre> |
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| <a name="addMissingPartitions-java.util.List-"> |
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| <h4>addMissingPartitions</h4> |
| <pre>public void addMissingPartitions(java.util.List<com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange> missingPartitions)</pre> |
| <div class="block">Capture partitions that are not currently being streamed. This should be the result of |
| observing the metadata table to identify missing StreamPartition rows. All the StreamPartitions |
| rows combined should form continuous, non-overlapping partitions covering all row keys. |
| |
| <p>Combine existing missing partitions and current (newly added) missing partitions. If missing |
| partitions have been missing for more than allotted time, it will be reconciled. |
| |
| <p>It is possible that a missing partition's boundary can change frequently, such that it can |
| take a long time to realize a partition is truly missing. For example, if [C, D) is missing, |
| but there are a lot of splits and merges around [C, D), we may see that sometimes [B,D) is |
| missing, or at other times [C-E) is missing due to split and merge activities of [B-C) and |
| [D-E), while [C-D) is truly missing. The moving boundaries would reset the timer leading to |
| slower reconciliation of the missing partition.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>missingPartitions</code> - partitions not being streamed.</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="addNewPartition-com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange-com.google.protobuf.ByteString-"> |
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| <h4>addNewPartition</h4> |
| <pre>public void addNewPartition(com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange partition, |
| com.google.protobuf.ByteString rowKey)</pre> |
| <div class="block">Capture NewPartition row that's waiting to be created. If any of these NewPartition row |
| overlaps with partition we notice are missing and needs to be reconciled, we will need to clean |
| up these NewPartition to avoid future conflicts and inconsistencies.</div> |
| <dl> |
| <dt><span class="paramLabel">Parameters:</span></dt> |
| <dd><code>partition</code> - new partitions waiting to be created.</dd> |
| <dd><code>rowKey</code> - the full row key of the new partition.</dd> |
| </dl> |
| </li> |
| </ul> |
| <a name="getPartitionsToReconcile--"> |
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| <h4>getPartitionsToReconcile</h4> |
| <pre>public java.util.HashMap<com.google.cloud.bigtable.data.v2.models.Range.ByteStringRange,java.util.Set<com.google.protobuf.ByteString>> getPartitionsToReconcile()</pre> |
| <div class="block">Match partitions that have been missing for a while and need to be reconciled with NewPartition |
| row key. Find NewPartition row key that overlaps with the reconciled partitions to clean them |
| up.</div> |
| <dl> |
| <dt><span class="returnLabel">Returns:</span></dt> |
| <dd>missing partitions and related NewPartition rows keys to delete.</dd> |
| </dl> |
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