Date: Thu, 19 Sep 2024 13:36:36 -0500
From: Nathan Bossart <nathandbossart@gmail.com>
To: Alexander Lakhin <exclusion@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, "Jonathan S. Katz" <jkatz@postgresql.org>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
Subject: Re: Large expressions in indexes can't be stored (non-TOASTable)
Message-ID: <ZuxvNDVfqpahqZNb@nathan>
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 <ZuroEfWjxd4Zj6Yq@nathan>
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On Thu, Sep 19, 2024 at 12:00:00PM +0300, Alexander Lakhin wrote:
> I've discovered that Jonathan's initial script:
> CREATE TABLE def (id int);
> SELECT array_agg(n) b FROM generate_series(1,10_000) n \gset
> CREATE OR REPLACE FUNCTION vec_quantizer (a int, b int[]) RETURNS bool
> AS $$ SELECT true $$ LANGUAGE SQL IMMUTABLE;
> CREATE INDEX ON def (vec_quantizer(id, :'b'));
> 
> completed with:
> DROP INDEX CONCURRENTLY def_vec_quantizer_idx;
> 
> triggers an assertion failure:
> TRAP: failed Assert("HaveRegisteredOrActiveSnapshot()"), File: "toast_internals.c", Line: 668, PID: 3723372

Ha, that was fast.  The attached patch seems to fix the assertion failures.
It's probably worth checking if any of the adjacent code paths are
affected, too.

-- 
nathan

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diff --git a/src/backend/catalog/index.c b/src/backend/catalog/index.c
index b2b3ecb524..2e378ef4ef 100644
--- a/src/backend/catalog/index.c
+++ b/src/backend/catalog/index.c
@@ -2255,6 +2255,7 @@ index_drop(Oid indexId, bool concurrent, bool concurrent_lock_mode)
 		PopActiveSnapshot();
 		CommitTransactionCommand();
 		StartTransactionCommand();
+		PushActiveSnapshot(GetTransactionSnapshot());
 
 		/*
 		 * Now we must wait until no running transaction could be using the
@@ -2283,8 +2284,10 @@ index_drop(Oid indexId, bool concurrent, bool concurrent_lock_mode)
 		 * Again, commit the transaction to make the pg_index update visible
 		 * to other sessions.
 		 */
+		PopActiveSnapshot();
 		CommitTransactionCommand();
 		StartTransactionCommand();
+		PushActiveSnapshot(GetTransactionSnapshot());
 
 		/*
 		 * Wait till every transaction that saw the old index state has
@@ -2387,6 +2390,8 @@ index_drop(Oid indexId, bool concurrent, bool concurrent_lock_mode)
 	{
 		UnlockRelationIdForSession(&heaprelid, ShareUpdateExclusiveLock);
 		UnlockRelationIdForSession(&indexrelid, ShareUpdateExclusiveLock);
+
+		PopActiveSnapshot();
 	}
 }
 

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