Set column name explicitely when using `current_database()` in queries #3526

kneth · 2025-02-16T06:22:33Z

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Postgres compatible databases like https://github.com/crate/crate can use PG JDBC as driver. Often the PG JDBC driver is used by a tool or integration (JetBrains DataGrip to name one). As CrateDB isn't fully PG compatible, this patch will make life a bit easier for our users. The issue has been reported as crate/crate#17393.

davecramer · 2025-02-18T16:48:15Z

I think I'd rather change all of the code referring to current_database to not use SQL at all. The connection knows the database. I don't thin it is necessary to use this function

jankohlmann · 2025-02-18T18:33:49Z

@davecramer are you thinking about reverting #3390 ?

davecramer · 2025-02-18T18:45:41Z

Probably not reverting it but changing the way it is done.
In the one you are changing you could simply do select 'db' as current_database where db is the database in the connection URL, or whatever is returned in the startup parameters

vlsi · 2025-02-19T05:57:07Z

Frankly, I see no issues leaving it as current_database() as current_database. I would probably prefer this one.

It would make query easier to understand and test. It would naturally avoid "concatenate string sql on every execution" as well.
WDYT?

vlsi · 2025-02-19T06:39:37Z

pgjdbc/src/test/java/org/postgresql/test/jdbc42/DatabaseMetaDataTest.java

+  void getColumnsForSchema() throws Exception {
+    DatabaseMetaData dbmd = conn.getMetaData();
+
+    ResultSet rs = dbmd.getColumns(null, "%", "decimaltest", "%");
+    assertTrue(rs.next());
+    assertEquals("a", rs.getString("COLUMN_NAME"));
+    assertEquals(0, rs.getInt("DECIMAL_DIGITS"));


Can we add a verification for the current_database column name?

I have added it to the test. Notice that getColumns reports the current database in the TABLE_CAT column: https://github.com/pgjdbc/pgjdbc/blob/master/pgjdbc/src/main/java/org/postgresql/jdbc/PgDatabaseMetaData.java#L1671

I thought current_database was returned via client=facing APIs, however, now I see it is used only in the internals.

However, it looks like the specific usage could be completely removed from SQL and we could use something like

byte[] catalogName = /* rs.getBytes("current_database") */; // replace with a known literal ... tuple[0] = catalogName;

Yes, I had this in mind as well.

Latest commit is removing current_database() where possible and use either the argument or use the connection's catalog name.

davecramer · 2025-02-19T10:04:11Z

Frankly, I see no issues leaving it as current_database() as current_database. I would probably prefer this one.

It would make query easier to understand and test. It would naturally avoid "concatenate string sql on every execution" as well. WDYT?

If #3528 fixes all of the performance regressions then we can leave this one as is.

kneth · 2025-02-19T10:32:05Z

Thank you for taken the time to review my PR. I have expanded the test as outlined in #3526 (review)

vlsi · 2025-02-19T12:05:51Z

, or whatever is returned in the startup parameters

It looks like the startup parameters do not return the database name.

At the same time, there's current_catalog function and information_schema.information_schema_catalog_name table returning catalog_name which is different from current_database.

So it looks like we should use those functions rather than current_database() if we want to treat catalogs somehow.
Is there a reason to ignore current_catalog PostgreSQL function?

davecramer · 2025-02-19T12:46:29Z

, or whatever is returned in the startup parameters

It looks like the startup parameters do not return the database name.

Interesting, somehow I though it was.

At the same time, there's current_catalog function and information_schema.information_schema_catalog_name table returning catalog_name which is different from current_database.

So it looks like we should use those functions rather than current_database() if we want to treat catalogs somehow. Is there a reason to ignore current_catalog PostgreSQL function?

Only if it creates a performance regression.

vlsi · 2025-02-21T08:18:56Z

Ok, PostgreSQL has a regression test that ensures current_database() should return the same value as current_catalog: https://github.com/postgres/postgres/blob/7d6d2c4bbd730bd9af191d46d4fb01d5f5c30cf1/src/test/regress/expected/expressions.out#L91-L94

At the same time, it looks like current_catalog was added for the SQL standard compatibility somewhere around 8.4.

So it is fine to keep using current_database().

vlsi · 2025-02-21T08:19:47Z

pgjdbc/src/main/java/org/postgresql/jdbc/PgDatabaseMetaData.java

@@ -57,6 +57,13 @@ public PgDatabaseMetaData(PgConnection conn) {
  private int nameDataLength; // length for name datatype
  private int indexMaxKeys; // maximum number of keys in an index.

+  private byte[] getCatalogName(@Nullable String catalog) throws SQLException {
+    if (catalog == null) {
+      return connection.getCatalog().getBytes();


We should use connection's encoding here. Otherwise there's a risk the bytes will be decoded differently

Good point - I have added the encoded

davecramer · 2025-02-21T10:53:17Z

Ok, PostgreSQL has a regression test that ensures current_database() should return the same value as current_catalog: https://github.com/postgres/postgres/blob/7d6d2c4bbd730bd9af191d46d4fb01d5f5c30cf1/src/test/regress/expected/expressions.out#L91-L94

At the same time, it looks like current_catalog was added for the SQL standard compatibility somewhere around 8.4.

So it is fine to keep using current_database().

Assuming no performance regression

kneth · 2025-02-27T15:49:52Z

@davecramer @vlsi Do you need any changes before you can merge my PR?

When merging, you should probably merge #3528 too so the performance is improved.

kneth · 2025-04-23T11:06:19Z

@davecramer @vlsi I have rebased my branch on master, and tests pass locally (gradlew test). Is it possible to advance the PR to a state where it can be merged?

davecramer · 2025-04-23T19:35:11Z

pgjdbc/src/main/java/org/postgresql/jdbc/PgDatabaseMetaData.java

+    }
+    return catalog.getBytes(Charset.defaultCharset());
+  }
+


From what I can tell we check to see if the catalog is null before calling this function.
Moot point: If we get a SQLException we should just throw it.

There are many checks like the following in the code:

if (catalog != null) { sql += " AND current_database() = " + escapeQuotes(catalog); }

They will not exclude null. Likewise, the additional checks in #3588 don't exclude catalog to be null afaik.

Removing the try/catch makes sense as errors can bubble up to the application.

In retrospect I should have removed all of those in #3588. By the time we get to the query we know that if the catalog is not null then it is the same as current_database() If you want to make those changes I'd appreciate it. Otherwise I'll make them which might make your's harder to rebase.

I'll take a look at it!

@davecramer @vlsi I gave it a shot, and I took the liberty to modify the condition as suggested in #3588 (comment)

davecramer · 2025-04-23T19:35:52Z

There's still a considerable amount of whitespace changes in this PR. Mostly around ( and beginning lines.

kneth · 2025-04-24T11:45:43Z

@davecramer says

[...] whitespace changes [...]

I have restored the white spaces

davecramer · 2025-04-24T17:25:23Z

Yes, checkstyle seems a little specific at times, but one more fix and we should be good to go

kneth · 2025-04-25T11:52:34Z

@davecramer

one more fix

... and done 😄

kneth · 2025-04-25T13:37:59Z

Thank you for merging

davecramer · 2025-04-25T13:39:04Z

Thank you for merging

Thank you for persisting through this process

kneth mentioned this pull request Feb 18, 2025

Improve compatibility with non-Postgres databases #3527

Closed

vlsi reviewed Feb 19, 2025

View reviewed changes

amotl mentioned this pull request Feb 19, 2025

JDBC: Update to pgjdbc 42.7.7 crate/crate-qa#333

Merged

vlsi reviewed Feb 21, 2025

View reviewed changes

kneth added 3 commits April 22, 2025 16:18

Set column name explicitely when using current_database() in queries

2d9b030

Check that current database is correctly reported

27218eb

factor out catalog name where possible

3b15692

kneth force-pushed the kneth/set-column-name-explicitely branch from 2fc2e79 to ab8e2fb Compare April 22, 2025 14:34

use connection's encoding

de7a693

kneth force-pushed the kneth/set-column-name-explicitely branch from ab8e2fb to de7a693 Compare April 22, 2025 14:49

kneth added 3 commits April 22, 2025 16:53

make style happy

08307c7

styling

49d0818

restore code formatting

4766e04

kneth force-pushed the kneth/set-column-name-explicitely branch from 798d192 to 4766e04 Compare April 23, 2025 09:47

kneth added 2 commits April 23, 2025 12:00

smaller improvements

501e743

small change to code format

ceeca4d

kneth force-pushed the kneth/set-column-name-explicitely branch from 88373e1 to ceeca4d Compare April 23, 2025 11:04

davecramer reviewed Apr 23, 2025

View reviewed changes

kneth added 2 commits April 24, 2025 11:22

Restore whitespaces

c5c3bdb

Don't silently ignore exceptions

8e6f12c

kneth force-pushed the kneth/set-column-name-explicitely branch from 7764e57 to 8e6f12c Compare April 24, 2025 11:25

Simplify boolean expression; drop check for null when not needed

5f5eb0f

kneth force-pushed the kneth/set-column-name-explicitely branch from 40414fe to 5f5eb0f Compare April 24, 2025 15:50

Making style checkers happy

532c217

davecramer merged commit 1e0c88d into pgjdbc:master Apr 25, 2025
15 of 17 checks passed

Set column name explicitely when using current_database() in queries #3526

Set column name explicitely when using current_database() in queries #3526

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Set column name explicitely when using `current_database()` in queries #3526

Set column name explicitely when using `current_database()` in queries #3526

kneth commented Feb 16, 2025 •

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