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The following commit(s) were added to refs/heads/branch-3.3 by this push:
new e98872fb5d07 [SPARK-46747][SQL] Avoid scan in getTableExistsQuery for
JDBC Dialects
e98872fb5d07 is described below
commit e98872fb5d07d570e6d0516b49a5d2e58876d1a6
Author: Kent Yao <y...@apache.org>
AuthorDate: Tue Jan 30 20:34:28 2024 +0800
[SPARK-46747][SQL] Avoid scan in getTableExistsQuery for JDBC Dialects
### What changes were proposed in this pull request?
[SPARK-46747](https://issues.apache.org/jira/browse/SPARK-46747) reported
an issue that Postgres instances suffered from too many shared locks, which was
caused by Spark‘s get table exist query. In this PR, we supplanted `"SELECT 1
FROM $table LIMIT 1"` with `"SELECT 1 FROM $table WHERE 1=0"` to prevent data
from being scanned.
### Why are the changes needed?
overhead reduction for JDBC datasources
### Does this PR introduce _any_ user-facing change?
no
### How was this patch tested?
existing JDBC v1/v2 datasouce tests.
### Was this patch authored or co-authored using generative AI tooling?
no
Closes #44948 from yaooqinn/SPARK-46747.
Authored-by: Kent Yao <y...@apache.org>
Signed-off-by: Kent Yao <y...@apache.org>
(cherry picked from commit 031df8fa62666f14f54cf0a792f7fa2acc43afee)
Signed-off-by: Kent Yao <y...@apache.org>
---
.../src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala | 2 +-
.../src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala | 4 ----
.../src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala | 4 ----
sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala | 7 +++----
4 files changed, 4 insertions(+), 13 deletions(-)
diff --git
a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala
b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala
index 1e65542946af..0cd46dda62c3 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcDialects.scala
@@ -141,7 +141,7 @@ abstract class JdbcDialect extends Serializable with
Logging{
* @return The SQL query to use for checking the table.
*/
def getTableExistsQuery(table: String): String = {
- s"SELECT * FROM $table WHERE 1=0"
+ s"SELECT 1 FROM $table WHERE 1=0"
}
/**
diff --git
a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala
b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala
index 24f9bac74f86..73903d65b01a 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/MySQLDialect.scala
@@ -94,10 +94,6 @@ private case object MySQLDialect extends JdbcDialect with
SQLConfHelper {
schemaBuilder.result
}
- override def getTableExistsQuery(table: String): String = {
- s"SELECT 1 FROM $table LIMIT 1"
- }
-
override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
// See https://dev.mysql.com/doc/refman/8.0/en/alter-table.html
diff --git
a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala
b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala
index a668d66ee2f9..6de4d6ec71a8 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala
@@ -141,10 +141,6 @@ private object PostgresDialect extends JdbcDialect with
SQLConfHelper {
case _ => None
}
- override def getTableExistsQuery(table: String): String = {
- s"SELECT 1 FROM $table LIMIT 1"
- }
-
override def isCascadingTruncateTable(): Option[Boolean] = Some(false)
/**
diff --git a/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala
b/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala
index a222391c06fb..74b85f18ceef 100644
--- a/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala
+++ b/sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala
@@ -989,10 +989,9 @@ class JDBCSuite extends QueryTest
val h2 = JdbcDialects.get(url)
val derby = JdbcDialects.get("jdbc:derby:db")
val table = "weblogs"
- val defaultQuery = s"SELECT * FROM $table WHERE 1=0"
- val limitQuery = s"SELECT 1 FROM $table LIMIT 1"
- assert(MySQL.getTableExistsQuery(table) == limitQuery)
- assert(Postgres.getTableExistsQuery(table) == limitQuery)
+ val defaultQuery = s"SELECT 1 FROM $table WHERE 1=0"
+ assert(MySQL.getTableExistsQuery(table) == defaultQuery)
+ assert(Postgres.getTableExistsQuery(table) == defaultQuery)
assert(db2.getTableExistsQuery(table) == defaultQuery)
assert(h2.getTableExistsQuery(table) == defaultQuery)
assert(derby.getTableExistsQuery(table) == defaultQuery)
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