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https://issues.apache.org/jira/browse/HDFS-17463?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17837689#comment-17837689
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ASF GitHub Bot commented on HDFS-17463:
---------------------------------------
XbaoWu commented on code in PR #6736:
URL: https://github.com/apache/hadoop/pull/6736#discussion_r1567230524
##########
hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/SerialNumberManager.java:
##########
@@ -115,6 +119,36 @@ public static StringTable getStringTable() {
return map;
}
+ // returns serial snapshot of current values for a save.
+ public static StringTable getSerialStringTable() {
+ // approximate size for capacity.
+ int size = 0;
+ for (final SerialNumberManager snm : values) {
+ size += snm.size();
+ }
+
+ int tableMaskBits = getMaskBits();
+ StringTable map = new StringTable(size, 0);
+ Set<String> entrySet = new HashSet<String>();
+ AtomicInteger index = new AtomicInteger();
+
+ Map <Integer, String> entryMap = new TreeMap<Integer, String>();
+ for (final SerialNumberManager snm : values) {
+ final int mask = snm.getMask(tableMaskBits);
+ for (Entry<Integer, String> entry : snm.entrySet()) {
+ entryMap.put(entry.getKey() | mask, entry.getValue());
+ }
+ }
+
+ entryMap.forEach((key, value) -> {
+ if(entrySet.add(value)){
+ map.put(index.incrementAndGet(), value);
Review Comment:
incrementAndGet method is executed when the fsimage file is persisted to
ensure that the index is continuous.
> Support the switch StringTable Split ID feature
> -----------------------------------------------
>
> Key: HDFS-17463
> URL: https://issues.apache.org/jira/browse/HDFS-17463
> Project: Hadoop HDFS
> Issue Type: Improvement
> Components: namenode
> Affects Versions: 3.2.0, 3.3.5, 3.3.3, 3.3.4
> Reporter: wangzhihui
> Priority: Major
> Labels: pull-request-available
> Attachments: Image_struct.png, error.png
>
>
> desc:
> *
> Hadoop 3.2 introduced optimization features for HDFS StringTable
> (b60ca37914b22550e3630fa02742d40697decb3), It resulted in lower versions of
> Hadoop upgraded to 3.2 and later versions not supporting downgrade
> operations.
> !error.png!
> * This issue has also been discussed in HDFS-14831, and it is recommended to
> revert the feature, but it cannot fundamentally solve the problem。
> *
> Therefore, we have added an optimization to support downgrading
>
> Solution:
> * First, we will add the "dfs. image. save. splitId. stringTable" conf
> switch "StringTable optimization feature" is enabled
> * When the conf value is false, an Image file compatible with lower versions
> of HDFS is generated to support downgrading.
> *
> The difference in HDFS Image file format between Hadoop 3.1.1 and Hadoop 3.2
> is shown in the following figure.
> * With the sub-sections feature introduced in HDFS-14617, Protobuf can
> support compatible reading.
> *
> The data structure causing incompatible differences is mainly StringTable.
> !Image_struct.png|width=396,height=163!
> * In "dfs.image.save.splitId.stringTable = false " the Id generation order
> of StringTable starts from 0 to Integer.Max. When true, the Id value range
> follows the latest rules.
>
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