yongzhi commented on a change in pull request #2826:
URL: https://github.com/apache/hive/pull/2826#discussion_r759297538
##########
File path:
standalone-metastore/metastore-server/src/main/java/org/apache/hadoop/hive/metastore/ObjectStore.java
##########
@@ -5275,38 +5275,67 @@ private void
removeUnusedColumnDescriptor(MColumnDescriptor oldCD) {
return;
}
- boolean success = false;
Query query = null;
+ Query query2 = null;
+ boolean success = false;
+ LOG.debug("execute removeUnusedColumnDescriptor");
+ DatabaseProduct dbProduct =
DatabaseProduct.determineDatabaseProduct(MetaStoreDirectSql.getProductName(pm),
conf);
+ /**
+ * In order to workaround oracle not supporting limit statement caused
performance issue, HIVE-9447 makes
+ * all the backend DB run select count(1) from SDS where SDS.CD_ID=? to
check if the specific CD_ID is
+ * referenced in SDS table before drop a partition. This select count(1)
statement does not scale well in
+ * Postgres, and there is no index for CD_ID column in SDS table.
+ * For a SDS table with with 1.5 million rows, select count(1) has average
700ms without index, while in
+ * 10-20ms with index. But the statement before
+ * HIVE-9447( SELECT * FROM "SDS" "A0" WHERE "A0"."CD_ID" = $1 limit 1)
uses less than 10ms .
+ */
try {
openTransaction();
- LOG.debug("execute removeUnusedColumnDescriptor");
-
- query = pm.newQuery("select count(1) from " +
- "org.apache.hadoop.hive.metastore.model.MStorageDescriptor where
(this.cd == inCD)");
- query.declareParameters("MColumnDescriptor inCD");
- long count = ((Long)query.execute(oldCD)).longValue();
-
- //if no other SD references this CD, we can throw it out.
- if (count == 0) {
- // First remove any constraints that may be associated with this CD
- query = pm.newQuery(MConstraint.class, "parentColumn == inCD ||
childColumn == inCD");
+ // Fix performance regression for postgres caused by HIVE-9447
+ if (dbProduct.isPOSTGRES() || dbProduct.isMYSQL()) {
+ query = pm.newQuery(MStorageDescriptor.class, "this.cd == inCD");
+ query.declareParameters("MColumnDescriptor inCD");
+ List<MStorageDescriptor> referencedSDs =
listStorageDescriptorsWithCD(oldCD, query);
+ //if no other SD references this CD, we can throw it out.
+ if (referencedSDs != null && referencedSDs.isEmpty()) {
Review comment:
removeConstraintsAndCd already centralizes the common code. I do not see
too much difference and I was trying to rebase as people already reviewed and
tested.
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