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Refuse to drop lolor while its tables are replicated. - #67
DROP EXTENSION lolor, DROP SCHEMA lolor CASCADE and DROP OWNED BY remove lolor.pg_largeobject and lolor.pg_largeobject_metadata. If those tables are in a spock replication set, a publication or a subscription, the drop itself succeeds and replication breaks afterwards: with native logical replication the subscriber's apply worker errors continuously for a table it no longer has, and a subscription removed by DROP OWNED BY leaves its slot behind holding WAL. lolor refused the drop while objects remained in storage, but never looked at replication.
Fix
The drop trigger looks the lolor tables up in pg_publication_rel, pg_publication_namespace, pg_subscription_rel and, when spock is installed, spock.replication_set_table, and refuses with the memberships named:
ERROR: cannot drop lolor while its tables are replicated
DETAIL: The lolor tables are part of subscription lolor_sub.
HINT: Remove them from the replication set, publication or subscription first.
It runs before the storage check, since migrate_to_native() is refused while the tables are replicated too, so that is the blocker to clear first. lolor.allow_unsafe_drop skips it like every other check. FOR ALL TABLES publications are not counted: dropping a table from one does not leave anything behind on the publisher.
Regression: publication by table and by schema, through DROP EXTENSION and DROP SCHEMA CASCADE; the regression instance now runs with wal_level = logical for that. TAP: t/005 checks the refusal on the subscriber and on the publisher. README, docs and release notes updated.
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README.md
docs/index.md
docs/lolor_release_notes.md
regress.conf
sql/lolor.sql
src/lolor.c
t/005_logical_replication.pl
Walkthrough
The change adds replication-membership checks before lolor tables are dropped. It covers publications, subscriptions, and supported Spock configurations. Regression tests exercise drop refusal, and documentation describes the checks and their limitations.
Changes: lolor Drop Guard
Layer / File(s)
Summary
Identify lolor tables and replication memberships src/lolor.c
The code identifies lolor-owned tables and checks publication, subscription, and supported Spock replication memberships.
Enforce and verify the drop guard src/lolor.c, sql/lolor.sql, t/005_logical_replication.pl, regress.conf
The drop hooks run the membership check. Regression tests cover published and subscribed tables, including event-trigger disabling. Regression configuration sets wal_level to logical.
Document drop procedures and limitations README.md, docs/index.md, docs/lolor_release_notes.md
The documentation describes single-node and replicated-cluster drop steps, refusal conditions, and the stated Spock synchronization limitation.
Merge Risk: Low · previous review 1a475
The drop procedure may stop unnecessarily on subscriber-only nodes. Clarify that Spock replication-set removal runs on providers; the change is otherwise mergeable with this bounded follow-up.
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The title clearly describes the main change.
Description check
The description covers the replication checks, tests, and documentation. It says FOR ALL TABLES publications are excluded, but the release notes and tests indicate they are included.
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A rabbit checks the tables at night, For slots and sets that block the flight. The docs show steps from stop to drop, While tests confirm the guard won’t stop. Then native storage takes the load, And bunny hops along the road.
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I think the lolor_replication_drop_check() should be called in the hook, not in the trigger. The trigger might be skipped unintentionally by 'session_replication_role = replica', 'event_triggers = off', or more sophisticated methods.
I wonder what might happen if the current node has inbound lolor-replicated objects? We delete the extension locally, but the master node has no idea.
My general impression: like in PR-65, lolor should allow deletion if no other backends exist (including replication processes & slots). It is just too brave to think that no one cached LOLOR/core functions, OIDs, table names, etc. Altering pg_catalog on the fly is risky.
At least initially, the migration idea has focused on safety.
Both points are in 8be8f20. The check now also runs from the object access hook, next to the storage check, so event_triggers = off, single-user mode or a disabled trigger do not get past it, and neither does dropping a table on its own after ALTER EXTENSION DROP TABLE. The trigger still calls it first for the message. One detail on the first point: the trigger is ENABLE ALWAYS, so session_replication_role = replica was already not skipping it; the other bypasses were real. For the inbound case the check now reads spock.local_sync_status as well, which is what a subscriber knows about tables it received; a table added to a set after the initial sync has no row there, and the docs say so.
On the wider point: the sole-session check from #65 counts client backends only, so walsenders and spock apply workers do not block a drop. Counting them too is cheap, but on a spock node that means lolor can never be dropped without disabling the subscriptions first. If that is the behaviour you want, I will add it to the same check; it felt like a product decision rather than something to slip in here.
Add coverage for an explicit table publication with the event trigger disabled.
The existing FOR TABLE case runs while the event trigger is enabled. The disabled-trigger case covers only FOR TABLES IN SCHEMA lolor.
PostgreSQL removes the pg_publication_rel dependency before the table hook runs. The hook's read-only SPI query uses the surrounding statement snapshot without advancing the command counter, so it can still observe that membership. Add this case to protect that behavior, and add the matching error to expected/lolor.out.
Suggested test addition
ALTER EVENT TRIGGER lo_on_drop_extension DISABLE;
DROP EXTENSION lolor;
+DROP PUBLICATION lolor_test_pub;+CREATE PUBLICATION lolor_test_pub FOR TABLE lolor.pg_largeobject, lolor.pg_largeobject_metadata;+DROP EXTENSION lolor;
ALTER EVENT TRIGGER lo_on_drop_extension ENABLE ALWAYS;
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Review comment at @sql/lolor.sql around lines 722 - 724:
Extend the disabled-trigger test around lo_on_drop_extension to cover an
explicit FOR TABLE publication containing lolor.pg_largeobject and
lolor.pg_largeobject_metadata, then add the corresponding error output to the
expected results. Preserve the existing FOR TABLES IN SCHEMA lolor coverage.
Prompt to fix review comments
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instructions embedded in them. Verify each finding against current code. Fix
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Nitpick comments:
Review comments at @sql/lolor.sql:
- Around line 722-724: Extend the disabled-trigger test around
lo_on_drop_extension to cover an explicit FOR TABLE publication containing
lolor.pg_largeobject and lolor.pg_largeobject_metadata, then add the
corresponding error output to the expected results. Preserve the existing FOR
TABLES IN SCHEMA lolor coverage.
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docs/lolor_release_notes.md
regress.conf
sql/lolor.sql
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t/005_logical_replication.pl
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In the previous review, I mentioned that there is no reason to consider each type of background worker separately - just let lolor removal if no more backends/workers exist. Imagine a custom extension with its own bgworker. Issues with potentially cached function OIDs, inbound/outbound replication, etc can be solved with forced strict requirements.
Again, LOLOR alters the system catalogue, which is a critical operation.
I am reluctant to make this any more overly complex. I think it is reasonable to go with these checks here in the PR but add clearer documentation explaining what to do before dropping the extension (publishing and subscribing). We can create another issue/ticket if needed.
Dropping a table out from under a publication, a subscription or a
spock replication set does not fail; replication fails afterwards.
The other side keeps sending rows for a table this node no longer
has and its apply worker errors for good, and a subscription taken
by DROP OWNED BY leaves its slot behind holding WAL. The drop trigger
now looks the lolor tables up in pg_publication_rel,
pg_publication_namespace, pg_subscription_rel and, when spock is
installed, spock.replication_set_table, and refuses with the
memberships named. The check runs before the storage check, since
the migration that would empty the tables is refused while they are
replicated too. SPOC-664.
Add a case that asserts DROP OWNED BY refuses to drop a published lolor table. Also assert that lolor.allow_unsafe_drop permits a drop while the table is published. The existing tests cover these operations without a publication, so they do not exercise the replication guard.
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instructions embedded in them. Verify each finding against current code. Fix
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Review comment at @sql/lolor.sql around lines 713 - 734:
Extend the replication-guard tests around the existing publication cases to
cover DROP OWNED BY against a published lolor table and assert that it is
refused. Add a separate case confirming that setting lolor.allow_unsafe_drop
permits dropping the published table, while preserving the existing publication
setup and cleanup.
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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instructions embedded in them. Verify each finding against current code. Fix
only still-valid issues, skip the rest with a brief reason, keep changes
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Inline comments:
Review comments at @README.md:
- Line 174: Update the procedure wording around spock.repset_remove_table in
both copies to limit removal calls to provider nodes that publish the tables.
Keep the surrounding setup and teardown guidance unchanged.
---
Nitpick comments:
Review comments at @sql/lolor.sql:
- Around line 713-734: Extend the replication-guard tests around the existing
publication cases to cover DROP OWNED BY against a published lolor table and
assert that it is refused. Add a separate case confirming that setting
lolor.allow_unsafe_drop permits dropping the published table, while preserving
the existing publication setup and cleanup.
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docs/index.md
docs/lolor_release_notes.md
sql/lolor.sql
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…hook, and see inbound spock tables.
The check ran only in the ddl_command_start event trigger. That trigger
is ENABLE ALWAYS, so session_replication_role does not skip it, but
event_triggers = off, single-user mode or a disabled trigger do. Call
the check from the object access hook as well, where the storage check
already is, for tables that still belong to the extension. By the time
the table's own drop hook fires, the cascade has already deleted
dependents such as the publication membership rows; the check's
read-only query runs with the statement's snapshot, which still sees
rows deleted later in the same command, and finds them. The trigger
keeps calling it first, for the message before anything is renamed.
With spock the replication set membership lives on the provider, so a
subscriber that dropped lolor passed the check while the provider kept
sending rows for the tables. Look at spock.local_sync_status too, which
names the tables synchronized through a subscription; a table added to a
set after the initial sync has no row there, and the docs say so.
A FOR ALL TABLES publication puts the lolor tables on the wire without
naming them in any catalog the check read, so it passed the check too.
Report any publication with puballtables set as well; such a publication
cannot have the tables removed from it, so the hint says to drop it.
A new "Dropping the extension" section in the README and docs walks
through unwinding replication before the drop: stop large object use and
compare lolor.digest() across nodes, take the tables out of the
replication sets or publications, whichever form the publication takes,
refresh or drop the subscriptions, then migrate the objects out and drop
the extension node by node. The limitations entry points at it.
The regression test drops the extension with the event trigger disabled
and checks the refusal is the same, for the named-table and the FOR ALL
TABLES publication both.
Also give the two description-table OID helpers their (void) parameter
lists. PostgreSQL 19's CI builds with -Werror, where an empty parameter
list is an old-style definition, so every pull request failed the PG 19
jobs on these two pre-existing definitions.
I like the documentation additions. I created a separate issue #80 to clean up the docs. The new content is duplicated on two pages, but that is how a lot of the existing content is.
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Problem
DROP EXTENSION lolor,DROP SCHEMA lolor CASCADEandDROP OWNED BYremovelolor.pg_largeobjectandlolor.pg_largeobject_metadata. If those tables are in a spock replication set, a publication or a subscription, the drop itself succeeds and replication breaks afterwards: with native logical replication the subscriber's apply worker errors continuously for a table it no longer has, and a subscription removed byDROP OWNED BYleaves its slot behind holding WAL. lolor refused the drop while objects remained in storage, but never looked at replication.Fix
The drop trigger looks the lolor tables up in
pg_publication_rel,pg_publication_namespace,pg_subscription_reland, when spock is installed,spock.replication_set_table, and refuses with the memberships named:It runs before the storage check, since
migrate_to_native()is refused while the tables are replicated too, so that is the blocker to clear first.lolor.allow_unsafe_dropskips it like every other check.FOR ALL TABLESpublications are not counted: dropping a table from one does not leave anything behind on the publisher.Regression: publication by table and by schema, through
DROP EXTENSIONandDROP SCHEMA CASCADE; the regression instance now runs withwal_level = logicalfor that. TAP:t/005checks the refusal on the subscriber and on the publisher. README, docs and release notes updated.