BELUGA BEHR created HIVE-20484:
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Summary: Disable Block Cache By Default With HBase SerDe
Key: HIVE-20484
URL: https://issues.apache.org/jira/browse/HIVE-20484
Project: Hive
Issue Type: Improvement
Components: HBase Handler
Affects Versions: 1.2.3, 2.4.0, 4.0.0, 3.2.0
Reporter: BELUGA BEHR
{quote}
Scan instances can be set to use the block cache in the RegionServer via the
setCacheBlocks method. For input Scans to MapReduce jobs, this should be false.
https://hbase.apache.org/book.html#perf.hbase.client.blockcache
{quote}
However, from the Hive code, we can see that this is not the case.
{code}
public static final String HBASE_SCAN_CACHEBLOCKS = "hbase.scan.cacheblock";
...
String scanCacheBlocks =
tableProperties.getProperty(HBaseSerDe.HBASE_SCAN_CACHEBLOCKS);
if (scanCacheBlocks != null) {
jobProperties.put(HBaseSerDe.HBASE_SCAN_CACHEBLOCKS, scanCacheBlocks);
}
...
String scanCacheBlocks = jobConf.get(HBaseSerDe.HBASE_SCAN_CACHEBLOCKS);
if (scanCacheBlocks != null) {
scan.setCacheBlocks(Boolean.parseBoolean(scanCacheBlocks));
}
{code}
In the Hive code, we can see that if {{hbase.scan.cacheblock}} is not specified
in the {{SERDEPROPERTIES}} then {{setCacheBlocks}} is not called and the
default value of the HBase {{Scan}} class is used.
{code:java|title=Scan.java}
/**
* Set whether blocks should be cached for this Scan.
* <p>
* This is true by default. When true, default settings of the table and
* family are used (this will never override caching blocks if the block
* cache is disabled for that family or entirely).
*
* @param cacheBlocks if false, default settings are overridden and blocks
* will not be cached
*/
public Scan setCacheBlocks(boolean cacheBlocks) {
this.cacheBlocks = cacheBlocks;
return this;
}
{code}
Hive is doing full scans of the table with MapReduce/Spark and therefore,
according to the HBase docs, the default behavior here should be that blocks
are not cached. Hive should set this value to "false" by default unless the
table {{SERDEPROPERTIES}} override this.
{code:sql}
-- Commands for HBase
-- create 'test', 't'
CREATE EXTERNAL TABLE test(value map<string,string>, row_key string)
STORED BY 'org.apache.hadoop.hive.hbase.HBaseStorageHandler'
WITH SERDEPROPERTIES (
"hbase.columns.mapping" = "t:,:key",
"hbase.scan.cacheblock" = "false"
);
{code}
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