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| <div class="sub-title"><span class="package-label-in-type">Package</span> <a href="package-summary.html">org.apache.storm.blobstore</a></div> |
| <h1 title="Class KeySequenceNumber" class="title">Class KeySequenceNumber</h1> |
| </div> |
| <div class="inheritance" title="Inheritance Tree"><a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">java.lang.Object</a> |
| <div class="inheritance">org.apache.storm.blobstore.KeySequenceNumber</div> |
| </div> |
| <section class="class-description" id="class-description"> |
| <hr> |
| <div class="type-signature"><span class="modifiers">public class </span><span class="element-name type-name-label">KeySequenceNumber</span> |
| <span class="extends-implements">extends <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">Object</a></span></div> |
| <div class="block">Class hands over the key sequence number which implies the number of updates made to a blob. |
| The information regarding the keys and the sequence number which represents the number of updates are |
| stored within the zookeeper in the following format. |
| /storm/blobstore/key_name/nimbushostport-sequencenumber |
| Example: |
| If there are two nimbodes with nimbus.seeds:leader,non-leader are set, |
| then the state inside the zookeeper is eventually stored as: |
| /storm/blobstore/key1/leader:8080-1 |
| /storm/blobstore/key1/non-leader:8080-1 |
| indicates that a new blob with the name key1 has been created on the leader |
| nimbus and the non-leader nimbus syncs after a call back is triggered by attempting |
| to download the blob and finally updates its state inside the zookeeper. |
| |
| <p>A watch is placed on the /storm/blobstore/key1 and the znodes leader:8080-1 and |
| non-leader:8080-1 are ephemeral which implies that these nodes exist only until the |
| connection between the corresponding nimbus and the zookeeper persist. If in case the |
| nimbus crashes the node disappears under /storm/blobstore/key1. |
| |
| <p>The sequence number for the keys are handed over based on the following scenario: |
| Lets assume there are three nimbodes up and running, one being the leader and the other |
| being the non-leader. |
| |
| <p>1. Create is straight forward. |
| Check whether the znode -> /storm/blobstore/key1 has been created or not. It implies |
| the blob has not been created yet. If not created, it creates it and updates the zookeeper |
| states under /storm/blobstore/key1 and /storm/blobstoremaxkeysequencenumber/key1. |
| The znodes it creates on these nodes are /storm/blobstore/key1/leader:8080-1, |
| /storm/blobstore/key1/non-leader:8080-1 and /storm/blobstoremaxkeysequencenumber/key1/1. |
| The latter holds the global sequence number across all nimbodes more like a static variable |
| indicating the true value of number of updates for a blob. This node helps to maintain sanity in case |
| leadership changes due to crashing. |
| |
| <p>2. Delete does not require to hand over the sequence number. |
| |
| <p>3. Finally, the update has few scenarios. |
| |
| <p>The class implements a TreeSet. The basic idea is if all the nimbodes have the same |
| sequence number for the blob, then the number of elements in the set is 1 which holds |
| the latest value of sequence number. If the number of elements are greater than 1 then it |
| implies that there is sequence mismatch and there is need for syncing the blobs across |
| nimbodes. |
| |
| <p>The logic for handing over sequence numbers based on the state are described as follows |
| Here consider Nimbus-1 alias as N1 and Nimbus-2 alias as N2. |
| Scenario 1: |
| Example: Normal create/update scenario |
| Operation Nimbus-1:state Nimbus-2:state Seq-Num-Nimbus-1 Seq-Num-Nimbus-2 Max-Seq-Num |
| Create-Key1 alive - Leader alive 1 1 |
| Sync alive - Leader alive 1 1 (callback -> download) 1 |
| Update-Key1 alive - Leader alive 2 1 2 |
| Sync alive - Leader alive 2 2 (callback -> download) 2 |
| |
| <p>Scenario 2: |
| Example: Leader nimbus crash followed by leader election, update and ex-leader restored again |
| Operation Nimbus-1:state Nimbus-2:state Seq-Num-Nimbus-1 Seq-Num-Nimbus-2 Max-Seq-Num |
| Create alive - Leader alive 1 1 |
| Sync alive - Leader alive 1 1 (callback -> download) 1 |
| Update alive - Leader alive 2 1 2 |
| Sync alive - Leader alive 2 2 (callback -> download) 2 |
| Update alive - Leader alive 3 2 3 |
| Crash crash - Leader alive 3 2 3 |
| New - Leader crash alive - Leader 3 (Invalid) 2 3 |
| Update crash alive - Leader 3 (Invalid) 4 (max-seq-num + 1) 4 |
| N1-Restored alive alive - Leader 0 4 4 |
| Sync alive alive - Leader 4 4 4 |
| |
| <p>Scenario 3: |
| Example: Leader nimbus crash followed by leader election, update and ex-leader restored again |
| Operation Nimbus-1:state Nimbus-2:state Seq-Num-Nimbus-1 Seq-Num-Nimbus-2 Max-Seq-Num |
| Create alive - Leader alive 1 1 |
| Sync alive - Leader alive 1 1 (callback -> download) 1 |
| Update alive - Leader alive 2 1 2 |
| Sync alive - Leader alive 2 2 (callback -> download) 2 |
| Update alive - Leader alive 3 2 3 |
| Crash crash - Leader alive 3 2 3 |
| Elect Leader crash alive - Leader 3 (Invalid) 2 3 |
| N1-Restored alive alive - Leader 3 2 3 |
| Read/Update alive alive - Leader 3 4 (Downloads from N1) 4 |
| Sync alive alive - Leader 4 (callback) 4 4 |
| Here the download is triggered whenever an operation corresponding to the blob is triggered on the |
| nimbus like a read or update operation. Here, in the read/update call it is hard to know which call |
| is read or update. Hence, by incrementing the sequence number to max-seq-num + 1 we ensure that the |
| synchronization happens appropriately and all nimbodes have the same blob.</div> |
| </section> |
| <section class="summary"> |
| <ul class="summary-list"> |
| <!-- ======== CONSTRUCTOR SUMMARY ======== --> |
| <li> |
| <section class="constructor-summary" id="constructor-summary"> |
| <h2>Constructor Summary</h2> |
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| <div class="summary-table two-column-summary"> |
| <div class="table-header col-first">Constructor</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-constructor-name even-row-color"><code><a href="#%3Cinit%3E(java.lang.String,org.apache.storm.nimbus.NimbusInfo)" class="member-name-link">KeySequenceNumber</a><wbr>(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a> key, |
| <a href="../nimbus/NimbusInfo.html" title="class in org.apache.storm.nimbus">NimbusInfo</a> nimbusInfo)</code></div> |
| <div class="col-last even-row-color"> </div> |
| </div> |
| </section> |
| </li> |
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| <section class="method-summary" id="method-summary"> |
| <h2>Method Summary</h2> |
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| <div class="table-header col-first">Modifier and Type</div> |
| <div class="table-header col-second">Method</div> |
| <div class="table-header col-last">Description</div> |
| <div class="col-first even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab4"><code>int</code></div> |
| <div class="col-second even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab4"><code><a href="#getKeySequenceNumber(org.apache.storm.shade.org.apache.curator.framework.CuratorFramework)" class="member-name-link">getKeySequenceNumber</a><wbr>(org.apache.storm.shade.org.apache.curator.framework.CuratorFramework zkClient)</code></div> |
| <div class="col-last even-row-color method-summary-table method-summary-table-tab2 method-summary-table-tab4"> </div> |
| </div> |
| </div> |
| </div> |
| <div class="inherited-list"> |
| <h3 id="methods-inherited-from-class-java.lang.Object">Methods inherited from class java.lang.<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html" title="class or interface in java.lang" class="external-link">Object</a></h3> |
| <code><a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#clone()" title="class or interface in java.lang" class="external-link">clone</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#equals(java.lang.Object)" title="class or interface in java.lang" class="external-link">equals</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#finalize()" title="class or interface in java.lang" class="external-link">finalize</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#getClass()" title="class or interface in java.lang" class="external-link">getClass</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#hashCode()" title="class or interface in java.lang" class="external-link">hashCode</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#notify()" title="class or interface in java.lang" class="external-link">notify</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#notifyAll()" title="class or interface in java.lang" class="external-link">notifyAll</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#toString()" title="class or interface in java.lang" class="external-link">toString</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#wait()" title="class or interface in java.lang" class="external-link">wait</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#wait(long)" title="class or interface in java.lang" class="external-link">wait</a>, <a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Object.html#wait(long,int)" title="class or interface in java.lang" class="external-link">wait</a></code></div> |
| </section> |
| </li> |
| </ul> |
| </section> |
| <section class="details"> |
| <ul class="details-list"> |
| <!-- ========= CONSTRUCTOR DETAIL ======== --> |
| <li> |
| <section class="constructor-details" id="constructor-detail"> |
| <h2>Constructor Details</h2> |
| <ul class="member-list"> |
| <li> |
| <section class="detail" id="<init>(java.lang.String,org.apache.storm.nimbus.NimbusInfo)"> |
| <h3>KeySequenceNumber</h3> |
| <div class="member-signature"><span class="modifiers">public</span> <span class="element-name">KeySequenceNumber</span><wbr><span class="parameters">(<a href="https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/String.html" title="class or interface in java.lang" class="external-link">String</a> key, |
| <a href="../nimbus/NimbusInfo.html" title="class in org.apache.storm.nimbus">NimbusInfo</a> nimbusInfo)</span></div> |
| </section> |
| </li> |
| </ul> |
| </section> |
| </li> |
| <!-- ============ METHOD DETAIL ========== --> |
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| <section class="method-details" id="method-detail"> |
| <h2>Method Details</h2> |
| <ul class="member-list"> |
| <li> |
| <section class="detail" id="getKeySequenceNumber(org.apache.storm.shade.org.apache.curator.framework.CuratorFramework)"> |
| <h3>getKeySequenceNumber</h3> |
| <div class="member-signature"><span class="modifiers">public</span> <span class="return-type">int</span> <span class="element-name">getKeySequenceNumber</span><wbr><span class="parameters">(org.apache.storm.shade.org.apache.curator.framework.CuratorFramework zkClient)</span> |
| throws <span class="exceptions"><a href="../generated/KeyNotFoundException.html" title="class in org.apache.storm.generated">KeyNotFoundException</a></span></div> |
| <dl class="notes"> |
| <dt>Throws:</dt> |
| <dd><code><a href="../generated/KeyNotFoundException.html" title="class in org.apache.storm.generated">KeyNotFoundException</a></code></dd> |
| </dl> |
| </section> |
| </li> |
| </ul> |
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| </li> |
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