Repository navigation
Optimizer extensions do not have access to query #549
Description
Hello,
after a solid couple of hours spent on debugging, I came to a conclusion that unfortunately behavior I encountered is a bug somewhere in DuckDB (my guess is duckdb-java, but it might as well be somewhere else).
I'm currently writing an extension, in which I wanted to capture user's queries. It worked just fine in DuckDB CLI, but when I loaded it into the JDBC version of DuckDB, it threw some nasty exceptions:
INTERNAL Error: Attempted to dereference unique_ptr that is NULL!
Stack Trace:
/home/miosp/.duckdb/extensions/v1.4.3/linux_amd64/my-extension.duckdb_extension(+0x782414) [0x7f004ccde414]
/home/miosp/.duckdb/extensions/v1.4.3/linux_amd64/my-extension.duckdb_extension(+0x7824bf) [0x7f004ccde4bf]
/home/miosp/.duckdb/extensions/v1.4.3/linux_amd64/my-extension.duckdb_extension(+0x784a71) [0x7f004cce0a71]
/home/miosp/.duckdb/extensions/v1.4.3/linux_amd64/my-extension.duckdb_extension(+0x20083a) [0x7f004c75c83a]
/home/miosp/.duckdb/extensions/v1.4.3/linux_amd64/my-extension.duckdb_extension(+0x47bc7f) [0x7f004c9d7c7f]
/tmp/libduckdb_java9599730312245461022.so(+0x128e924) [0x7f007a33b924]
/tmp/libduckdb_java9599730312245461022.so(+0x128ea5c) [0x7f007a33ba5c]
/tmp/libduckdb_java9599730312245461022.so(+0x1290674) [0x7f007a33d674]
/tmp/libduckdb_java9599730312245461022.so(+0x118488f) [0x7f007a23188f]
/tmp/libduckdb_java9599730312245461022.so(+0x1184ba1) [0x7f007a231ba1]
/tmp/libduckdb_java9599730312245461022.so(+0x1184fac) [0x7f007a231fac]
/tmp/libduckdb_java9599730312245461022.so(+0x1167ffc) [0x7f007a214ffc]
/tmp/libduckdb_java9599730312245461022.so(+0x11681ed) [0x7f007a2151ed]
/tmp/libduckdb_java9599730312245461022.so(+0x118e2c5) [0x7f007a23b2c5]
/tmp/libduckdb_java9599730312245461022.so(+0x118e36b) [0x7f007a23b36b]
/tmp/libduckdb_java9599730312245461022.so(+0x509315) [0x7f00795b6315]
/tmp/libduckdb_java9599730312245461022.so(Java_org_duckdb_DuckDBNative_duckdb_1jdbc_1prepare+0x11) [0x7f00795ba141]
[0x7f02e626eb6d]
I tried to dig into the issue and i developed a minimal PoC of the issue (strapped onto the extension template repository and switched both DuckDB and CI tools versions to 1.4.3 to be sure).
Then, I modified the quack_extension.cpp to:
#define DUCKDB_EXTENSION_MAIN
#include "quack_extension.hpp"
#include "duckdb.hpp"
#include "duckdb/common/exception.hpp"
#include "duckdb/function/scalar_function.hpp"
#include <duckdb/parser/parsed_data/create_scalar_function_info.hpp>
namespace duckdb {
void PreOptimize(OptimizerExtensionInput &input, unique_ptr<LogicalOperator> &plan) {
if (!plan) {
return;
}
string query;
try {
query = input.context.GetCurrentQuery();
} catch (...) {
Printer::Print("Caught some Exception");
return;
}
Printer::Print("QuackExtension PreOptimize called for query: " + query);
return;
}
static void LoadInternal(ExtensionLoader &loader) {
auto &db_instance = loader.GetDatabaseInstance();
auto &config = db_instance.config;
OptimizerExtension extension;
extension.pre_optimize_function = &PreOptimize;
config.optimizer_extensions.push_back(extension);
}
void QuackExtension::Load(ExtensionLoader &loader) {
LoadInternal(loader);
}
std::string QuackExtension::Name() {
return "quack";
}
std::string QuackExtension::Version() const {
#ifdef EXT_VERSION_QUACK
return EXT_VERSION_QUACK;
#else
return "";
#endif
}
} // namespace duckdb
extern "C" {
DUCKDB_CPP_EXTENSION_ENTRY(quack, loader) {
duckdb::LoadInternal(loader);
}
}When i launch the extension from the CLI i get:
duckdb -unsigned
DuckDB v1.4.3 (Andium) d1dc88f950
Enter ".help" for usage hints.
D LOAD '/home/miosp/proj/extension-template/build/release/repository/v1.4.3/linux_amd64/quack.duckdb_extension';
D pragma VERSION;
QuackExtension PreOptimize called for query: SELECT * FROM pragma_version();
┌─────────────────┬────────────┬──────────┐
│ library_version │ source_id │ codename │
│ varchar │ varchar │ varchar │
├─────────────────┼────────────┼──────────┤
│ v1.4.3 │ d1dc88f950 │ Andium │
└─────────────────┴────────────┴──────────┘
But through the Java JDBC driver I get (after issuing the same commands programatically):
Caught some Exception
So the output is still correct, but the query was not attached to the context.
I also noticed that if I connect DuckLake to my JDBC DuckDB, the auxiliary queries are caught correctly (I believe this one is for SHOW ALL TABLES;):
QuackExtension PreOptimize called for query: BEGIN TRANSACTION
QuackExtension PreOptimize called for query:
SELECT * FROM postgres_query('__ducklake_metadata_miosp_ducklake',
'SELECT snapshot_id, schema_version, next_catalog_id, next_file_id
FROM "public".ducklake_snapshot WHERE snapshot_id = (
SELECT MAX(snapshot_id) FROM "public".ducklake_snapshot
);')
QuackExtension PreOptimize called for query: COMMIT
QuackExtension PreOptimize called for query: BEGIN TRANSACTION
QuackExtension PreOptimize called for query:
SELECT * FROM postgres_query('__ducklake_metadata_miosp_ducklake',
'SELECT snapshot_id, schema_version, next_catalog_id, next_file_id
FROM "public".ducklake_snapshot WHERE snapshot_id = (
SELECT MAX(snapshot_id) FROM "public".ducklake_snapshot
);')
Caught some Exception
QuackExtension PreOptimize called for query: COMMIT
Caught some Exception
Caught some Exception
QuackExtension PreOptimize called for query: BEGIN TRANSACTION
QuackExtension PreOptimize called for query:
SELECT * FROM postgres_query('__ducklake_metadata_miosp_ducklake',
'SELECT snapshot_id, schema_version, next_catalog_id, next_file_id
FROM "public".ducklake_snapshot WHERE snapshot_id = (
SELECT MAX(snapshot_id) FROM "public".ducklake_snapshot
);')
QuackExtension PreOptimize called for query: COMMIT
Caught some Exception
Am I doing something wrong, or this is a legitimate bug?
Activity
staticlibs commentedon Jan 29, 2026
Hi, thanks for the report!
What is this exception that is being caught here? Is it the same every time?
Miosp commentedon Jan 29, 2026
Take a look at the code, I just hardcoded-in the string. In general the
active_queryfrom the context seems to benullptr, so theinput.context.GetCurrentQuery();fails. This always seems to be the cause of my original unique_ptr dereferencing exception.thijs-s commentedon Jan 30, 2026
we had similar problem, here is a potential fix duckdb/duckdb#20755