Upgrade pgvector to 0.7.0.
This PR is based on Heikki's PR #6753 and just uses pgvector 0.7.0
instead of 0.6.0
I have now done all planned manual tests.
The pull request is ready to be reviewed and merged and can be deployed
in production together / after swap enablement.
See (https://github.com/neondatabase/autoscaling/issues/800)
Fixes https://github.com/neondatabase/neon/issues/6516
Fixes https://github.com/neondatabase/neon/issues/7780
## Documentation input for usage recommendations
### maintenance_work_mem
In Neon
`maintenance_work_mem` is very small by default (depends on configured
RAM for your compute but can be as low as 64 MB).
To optimize pgvector index build time you may have to bump it up
according to your working set size (size of tuples for vector index
creation).
You can do so in the current session using
`SET maintenance_work_mem='10 GB';`
The target value you choose should fit into the memory of your compute
size and not exceed 50-60% of available RAM.
The value above has been successfully used on a 7CU endpoint.
### max_parallel_maintenance_workers
max_parallel_maintenance_workers is also small by default (2). For
efficient parallel pgvector index creation you have to bump it up with
`SET max_parallel_maintenance_workers = 7`
to make use of all the CPUs available, assuming you have configured your
endpoint to use 7CU.
## ID input for changelog
pgvector extension in Neon has been upgraded from version 0.5.1 to
version 0.7.0.
Please see https://github.com/pgvector/pgvector/ for documentation of
new capabilities in pgvector version 0.7.0
If you have existing databases with pgvector 0.5.1 already installed
there is a slight difference in behavior in the following corner cases
even if you don't run `ALTER EXTENSION UPDATE`:
### L2 distance from NULL::vector
For the following script, comparing the NULL::vector to non-null vectors
the resulting output changes:
```sql
SET enable_seqscan = off;
CREATE TABLE t (val vector(3));
INSERT INTO t (val) VALUES ('[0,0,0]'), ('[1,2,3]'), ('[1,1,1]'), (NULL);
CREATE INDEX ON t USING hnsw (val vector_l2_ops);
INSERT INTO t (val) VALUES ('[1,2,4]');
SELECT * FROM t ORDER BY val <-> (SELECT NULL::vector);
```
and now the output is
```
val
---------
[1,1,1]
[1,2,4]
[1,2,3]
[0,0,0]
(4 rows)
```
For the following script
```sql
SET enable_seqscan = off;
CREATE TABLE t (val vector(3));
INSERT INTO t (val) VALUES ('[0,0,0]'), ('[1,2,3]'), ('[1,1,1]'), (NULL);
CREATE INDEX ON t USING ivfflat (val vector_l2_ops) WITH (lists = 1);
INSERT INTO t (val) VALUES ('[1,2,4]');
SELECT * FROM t ORDER BY val <-> (SELECT NULL::vector);
```
the output now is
```
val
---------
[0,0,0]
[1,2,3]
[1,1,1]
[1,2,4]
(4 rows)
```
### changed error messages
If you provide invalid literals for datatype vector you may get
improved/changed error messages, for example:
```sql
neondb=> SELECT '[4e38,1]'::vector;
ERROR: "4e38" is out of range for type vector
LINE 1: SELECT '[4e38,1]'::vector;
^
```
---------
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
The issue is still unsolved because of shmem size in VMs. Need to figure it out before applying this patch.
For more details:
```
ERROR: could not resize shared memory segment "/PostgreSQL.2892504480" to 16774205952 bytes: No space left on device
```
As an example, the same issue in community pgvector/pgvector#453.
This includes a compatibility patch that is needed because pgvector
now skips WAL-logging during the index build, and WAL-logs the index
only in one go at the end. That's how GIN, GiST and SP-GIST index
builds work in core PostgreSQL too, but we need some Neon-specific
calls to mark the beginning and end of those build phases.
pgvector is the first index AM that does that with parallel workers,
so I had to modify those functions in the Neon extension to be aware
of parallel workers. Only the leader needs to create the underlying
file and perform the WAL-logging. (In principle, the parallel workers
could participate in the WAL-logging too, but pgvector doesn't do
that. This will need some further work if that changes).
The previous attempt at this (#6592) missed that parallel workers
needed those changes, and segfaulted in parallel build that spilled to
disk.
Testing
-------
We don't have a place for regression tests of extensions at the
moment. I tested this manually with the following script:
```
CREATE EXTENSION IF NOT EXISTS vector;
DROP TABLE IF EXISTS tst;
CREATE TABLE tst (i serial, v vector(3));
INSERT INTO tst (v) SELECT ARRAY[random(), random(), random()] FROM generate_series(1, 15000) g;
-- Serial build, in memory
ALTER TABLE tst SET (parallel_workers=0);
SET maintenance_work_mem='50 MB';
CREATE INDEX idx ON tst USING hnsw (v vector_l2_ops);
-- Test that the index works. (The table contents are random, and the
-- search is approximate anyway, so we cannot check the exact values.
-- For now, just eyeball that they look reasonable)
set enable_seqscan=off;
explain SELECT * FROM tst ORDER BY v <-> ARRAY[0, 0, 0]::vector LIMIT 5;
SELECT * FROM tst ORDER BY v <-> ARRAY[0, 0, 0]::vector LIMIT 5;
DROP INDEX idx;
-- Serial build, spills to on disk
ALTER TABLE tst SET (parallel_workers=0);
SET maintenance_work_mem='5 MB';
CREATE INDEX idx ON tst USING hnsw (v vector_l2_ops);
SELECT * FROM tst ORDER BY v <-> ARRAY[0, 0, 0]::vector LIMIT 5;
DROP INDEX idx;
-- Parallel build, in memory
ALTER TABLE tst SET (parallel_workers=4);
SET maintenance_work_mem='50 MB';
CREATE INDEX idx ON tst USING hnsw (v vector_l2_ops);
SELECT * FROM tst ORDER BY v <-> ARRAY[0, 0, 0]::vector LIMIT 5;
DROP INDEX idx;
-- Parallel build, spills to disk
ALTER TABLE tst SET (parallel_workers=4);
SET maintenance_work_mem='5 MB';
CREATE INDEX idx ON tst USING hnsw (v vector_l2_ops);
SELECT * FROM tst ORDER BY v <-> ARRAY[0, 0, 0]::vector LIMIT 5;
DROP INDEX idx;
```
