Optimise PostgresMetadataFetcher

document-store/src/main/java/org/hypertrace/core/documentstore/postgres/PostgresMetadataFetcher.java

@@ -5,61 +5,61 @@
 import java.sql.ResultSet;
 import java.sql.SQLException;
 import java.util.HashMap;
-import java.util.HashSet;
 import java.util.Map;
-import java.util.Set;
 import lombok.AllArgsConstructor;
 import org.hypertrace.core.documentstore.expression.impl.DataType;
 import org.hypertrace.core.documentstore.postgres.model.PostgresColumnMetadata;
 import org.hypertrace.core.documentstore.postgres.query.v1.parser.filter.nonjson.field.PostgresDataType;
-import org.hypertrace.core.documentstore.postgres.utils.PostgresUtils;
 
-/**
- * Fetches schema metadata directly from Postgres system catalogs. Hardcoded to query
- * information_schema.columns.
- */
+/** Fetches schema metadata directly from Postgres system catalogs (pg_catalog). */
 @AllArgsConstructor
 public class PostgresMetadataFetcher {
 
   private final PostgresClient client;
 
   private static final String DISCOVERY_SQL =
-      "SELECT column_name, udt_name, is_nullable "
-          + "FROM information_schema.columns "
-          + "WHERE table_schema = 'public' AND table_name = ?";
-
-  private static final String PRIMARY_KEY_SQL =
-      "SELECT a.attname as column_name "
-          + "FROM pg_index i "
-          + "JOIN pg_attribute a ON a.attrelid = i.indrelid AND a.attnum = ANY(i.indkey) "
-          + "WHERE i.indrelid = ?::regclass AND i.indisprimary";
+      "SELECT a.attname AS column_name, "
+          + "t.typname AS udt_name, "
+          + "NOT a.attnotnull AS is_nullable, "
+          + "COALESCE(pk.is_pk, false) AS is_primary_key "
+          + "FROM pg_attribute a "
+          + "JOIN pg_class c ON a.attrelid = c.oid "
+          + "JOIN pg_namespace n ON c.relnamespace = n.oid "
+          + "JOIN pg_type t ON a.atttypid = t.oid "
+          + "LEFT JOIN ( "
+          + "  SELECT a2.attname, true AS is_pk "
+          + "  FROM pg_index i "
+          + "  JOIN pg_attribute a2 ON a2.attrelid = i.indrelid AND a2.attnum = ANY(i.indkey) "
+          + "  WHERE i.indisprimary "
+          + ") pk ON pk.attname = a.attname "
+          + "WHERE c.relname = ? "
+          + "AND n.nspname = 'public' "
+          + "AND a.attnum > 0 "
+          + "AND NOT a.attisdropped";
 
   public Map<String, PostgresColumnMetadata> fetch(String tableName) {
     Map<String, PostgresColumnMetadata> metadataMap = new HashMap<>();
 
-    try (Connection conn = client.getPooledConnection()) {
-      Set<String> primaryKeyColumns = fetchPrimaryKeyColumns(conn, tableName);
-
-      try (PreparedStatement ps = conn.prepareStatement(DISCOVERY_SQL)) {
-        ps.setString(1, tableName);
-        try (ResultSet rs = ps.executeQuery()) {
-          while (rs.next()) {
-            String columnName = rs.getString("column_name");
-            String udtName = rs.getString("udt_name");
-            boolean isNullable = "YES".equalsIgnoreCase(rs.getString("is_nullable"));
-            boolean isArray = udtName != null && udtName.startsWith("_");
-            String baseType = isArray ? udtName.substring(1) : udtName;
-            boolean isPrimaryKey = primaryKeyColumns.contains(columnName);
-            metadataMap.put(
-                columnName,
-                new PostgresColumnMetadata(
-                    columnName,
-                    mapToCanonicalType(baseType),
-                    mapToPostgresType(baseType),
-                    isNullable,
-                    isArray,
-                    isPrimaryKey));
-          }
+    try (Connection conn = client.getPooledConnection();
+        PreparedStatement ps = conn.prepareStatement(DISCOVERY_SQL)) {
+      ps.setString(1, tableName);
+      try (ResultSet rs = ps.executeQuery()) {
+        while (rs.next()) {
+          String columnName = rs.getString("column_name");
+          String udtName = rs.getString("udt_name");
+          boolean isNullable = rs.getBoolean("is_nullable");
+          boolean isArray = udtName != null && udtName.startsWith("_");
+          String baseType = isArray ? udtName.substring(1) : udtName;
+          boolean isPrimaryKey = rs.getBoolean("is_primary_key");
+          metadataMap.put(
+              columnName,
+              new PostgresColumnMetadata(
+                  columnName,
+                  mapToCanonicalType(baseType),
+                  mapToPostgresType(baseType),
+                  isNullable,
+                  isArray,
+                  isPrimaryKey));
         }
       }
       return metadataMap;
@@ -68,20 +68,6 @@ public Map<String, PostgresColumnMetadata> fetch(String tableName) {
     }
   }
 
-  private Set<String> fetchPrimaryKeyColumns(Connection conn, String tableName)
-      throws SQLException {
-    Set<String> pkColumns = new HashSet<>();
-    try (PreparedStatement ps = conn.prepareStatement(PRIMARY_KEY_SQL)) {
-      ps.setString(1, PostgresUtils.wrapFieldNamesWithDoubleQuotes(tableName));
-      try (ResultSet rs = ps.executeQuery()) {
-        while (rs.next()) {
-          pkColumns.add(rs.getString("column_name"));
-        }
-      }
-    }
-    return pkColumns;
-  }
-
   /** Maps Postgres udt_name to canonical DataType. */
   private DataType mapToCanonicalType(String udtName) {
     if (udtName == null) {