Re: [WIP]Vertical Clustered Index (columnar store extension) - take2 - Mailing list pgsql-hackers

On Tue, 29 Jul 2025 at 06:57, Peter Smith <smithpb2250@gmail.com> wrote:
> Here are the latest v15 patches.
>
> Changes include:
>
> PATCH 0002.
> - README now says user should not tamper with VCI internal relations
> - fixes/test the VACUUM bug -- fix provided by Japin [1]
> - fixes/tests the reported segv for attempted REFRESH of VCI internal
> relation -- see [2 comment#1]
> - fixes/tests VCI internal relation dependency on the indexed table
> - simplifies code for PG_TEMP_FILES_DIR -- see [2 comment#2]
>

Hi Peter,

Thanks for updating the patches.

1.
I've identified another TRAP failure. Here are the reproduction steps:

rm -rf demo
initdb -D demo
cat <<EOF >>demo/postgresql.auto.conf
shared_preload_libraries = 'vci'
max_worker_processes = '20'
EOF

pg_ctl -D demo start

cat <<EOF | psql postgres
CREATE EXTENSION vci;
CREATE TABLE t (id int, info text);
CREATE INDEX ON t USING vci (id);
INSERT INTO t SELECT id, md5(random()::text) FROM generate_series(1, 1000) id;
REINDEX TABLE t;
REINDEX TABLE t;
EOF

The current VCI design doesn't support REINDEX, which is expected. But I've
discovered an unexpected issue: running REINDEX on a table a second time causes
an assertion failure.


2.
+Internal Relation Types:
+- -1:  TID relation (maps CRID to original TID)
+- -2:  NULL vector (bit array for NULL values)
+- -3:  Delete vector (bit array for deleted records)
+- -5:  TID-CRID mapping table
+- -9:  Data WOS (buffered row data)
+- -10: Whiteout WOS (deletion markers)
+- 0-N: ROS column data relations (one per indexed column)
+
+Example:
+For a VCI index on sales(customer_id, amount, date):
+
+Generated relations include:
+vci_0000001234_00000_d  → Column 0 data (customer_id)
+vci_0000001234_00001_d  → Column 1 data (amount)
+vci_0000001234_00002_d  → Column 2 data (date)
+vci_0000001234_65535_d  → TID relation
+vci_0000001234_65534_d  → NULL vector
+vci_0000001234_65533_d  → Delete vector
+vci_0000001234_65531_m  → TID-CRID mapping
+vci_0000001234_65527_d  → Data WOS
+vci_0000001234_65526_d  → Whiteout WOS

The README states that it generates the above relations, but there are
additional internal relations that are not mentioned.

SELECT relname, relkind FROM pg_class WHERE relname ~ 'vci*' ORDER BY relname;
        relname         | relkind
------------------------+---------
 vci_0000016578_00000_d | m
 vci_0000016578_00000_m | m
 vci_0000016578_00001_d | m
 vci_0000016578_00001_m | m
 vci_0000016578_65526_d | m
 vci_0000016578_65527_d | m
 vci_0000016578_65530_0 | m
 vci_0000016578_65530_1 | m
 vci_0000016578_65531_d | m
 vci_0000016578_65531_m | m
 vci_0000016578_65533_d | m
 vci_0000016578_65533_m | m
 vci_0000016578_65534_d | m
 vci_0000016578_65534_m | m
 vci_0000016578_65535_d | m
 vci_0000016578_65535_m | m

Based on the above, are the following materialized views unused, or is their
use just undocumented?

  - vci_0000016578_00000_m
  - vci_0000016578_00001_m
  - vci_0000016491_65530_0
  - vci_0000016578_65530_1
  - vci_0000016578_65531_d
  - vci_0000016578_65534_m
  - vci_0000016578_65535_m

What is the purpose of the '0' and '1' suffixes?


3.
I've also found that the VCI index is not working. Is this the expected
behavior?

[local]:3209161 postgres=# \d+ t
                                            Table "public.t"
 Column |  Type   | Collation | Nullable | Default | Storage  | Compression | Stats target | Description
--------+---------+-----------+----------+---------+----------+-------------+--------------+-------------
 id     | integer |           |          |         | plain    |             |              |
 info   | text    |           |          |         | extended |             |              |
Indexes:
    "t_id_idx" vci (id)
Access method: heap

[local]:3209161 postgres=# SET enable_seqscan TO off;
SET
[local]:3209161 postgres=# EXPLAIN SELECT * FROM t WHERE id = 1000;
                     QUERY PLAN
-----------------------------------------------------
 Seq Scan on t  (cost=0.00..2084.00 rows=1 width=37)
   Disabled: true
   Filter: (id = 1000)
(3 rows)

--
Regards,
Japin Li