JDBC access hangs when using postgres driver with fastpath to read large objects

[ykonrad]

PgDog version
v0.1.38

JDBC access hangs when using postgres fastpath to read large objects. I tried both session and transaction pool types

Symptom: Fastpath F message sent by JDBC's LargeObjectManager gets no response, thread hangs indefinitely

SQL-based (psql) lo_open/loread work fine through PgDog; hang only happens with JDBC's Fastpath wire message

Java thread hangs on:

java.lang.Thread.State: RUNNABLE
at sun.nio.ch.Net.poll(java.base@25.0.1/Native Method)
at sun.nio.ch.NioSocketImpl.park(java.base@25.0.1/NioSocketImpl.java:190)
at sun.nio.ch.NioSocketImpl.park(java.base@25.0.1/NioSocketImpl.java:200)
at sun.nio.ch.NioSocketImpl.implRead(java.base@25.0.1/NioSocketImpl.java:307)
at sun.nio.ch.NioSocketImpl.read(java.base@25.0.1/NioSocketImpl.java:354)
at sun.nio.ch.NioSocketImpl$1.read(java.base@25.0.1/NioSocketImpl.java:798)
at java.net.Socket$SocketInputStream.implRead(java.base@25.0.1/Socket.java:974)
at java.net.Socket$SocketInputStream.read(java.base@25.0.1/Socket.java:964)
at org.postgresql.core.VisibleBufferedInputStream.readMore(VisibleBufferedInputStream.java:192)
at org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:159)
at org.postgresql.core.VisibleBufferedInputStream.ensureBytes(VisibleBufferedInputStream.java:144)
at org.postgresql.core.VisibleBufferedInputStream.read(VisibleBufferedInputStream.java:76)
at org.postgresql.core.PGStream.receiveChar(PGStream.java:476)
at org.postgresql.core.v3.QueryExecutorImpl.receiveFastpathResult(QueryExecutorImpl.java:881)
at org.postgresql.core.v3.QueryExecutorImpl.fastpathCall(QueryExecutorImpl.java:669)
at org.postgresql.fastpath.Fastpath.fastpath(Fastpath.java:110)
at org.postgresql.fastpath.Fastpath.fastpath(Fastpath.java:152)
at org.postgresql.fastpath.Fastpath.getInteger(Fastpath.java:164)
at org.postgresql.largeobject.LargeObject.(LargeObject.java:107)
at org.postgresql.largeobject.LargeObjectManager.open(LargeObjectManager.java:247)
at org.postgresql.largeobject.LargeObjectManager.open(LargeObjectManager.java:230)
at org.postgresql.jdbc.AbstractBlobClob.getLo(AbstractBlobClob.java:288)
at org.postgresql.jdbc.AbstractBlobClob.getBinaryStream(AbstractBlobClob.java:127)
at org.postgresql.jdbc.PgClob.getCharacterStream(PgClob.java:76)
at org.hibernate.type.descriptor.java.DataHelper.extractString(DataHelper.java:263)
at org.hibernate.type.descriptor.java.StringTypeDescriptor.wrap(StringTypeDescriptor.java:75)
at org.hibernate.type.descriptor.java.StringTypeDescriptor.wrap(StringTypeDescriptor.java:22)
at org.hibernate.type.descriptor.sql.ClobTypeDescriptor$1.doExtract(ClobTypeDescriptor.java:44)
at org.hibernate.type.descriptor.sql.BasicExtractor.extract(BasicExtractor.java:47)
at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:260)
at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:256)
at org.hibernate.type.AbstractStandardBasicType.nullSafeGet(AbstractStandardBasicType.java:252)
at org.hibernate.loader.criteria.CriteriaLoader.getResultRow(CriteriaLoader.java:161)
at org.hibernate.loader.criteria.CriteriaLoader.getResultColumnOrRow(CriteriaLoader.java:141)

[ykonrad]

This is working with pgbouncer for both pool types

[meskill]

Yes, there is no proper handling for F messages sent through pgdog and this could lead to hanging. I think the FastPath API is considered obsolete and I'm not sure if we should fully support it.
I'll try to prepare the fix that will properly forward messages for this through pgdog and see if it'll be enough to fix it.

[ykonrad]

the latest driver (42.7.6, released May 2025) actually went in the opposite direction it un-deprecated the Fastpath API, they decided to keep it as a supported mechanism most likely. There is no roadmap to replace LOB access with prepared statements internally.

Do you see any ETA for FastPath support in pgdog (transaction pooling preferred)?

[meskill]

Already prepared the fix #957

[ykonrad]

Superb. Just made quick smoke test for it and it is working like charm. Thanks!!