## Problem
We currently have this code duplicated across different PG versions.
Moving this to an extension would reduce duplication and simplify
maintenance.
## Summary of changes
Moving the LastWrittenLSN code from PG versions to the Neon extension
and linking it with hooks.
Related Postgres PR: https://github.com/neondatabase/postgres/pull/590
Closes: https://github.com/neondatabase/neon/issues/10973
---------
Co-authored-by: Tristan Partin <tristan@neon.tech>
## Problem
Both these versions are binary compatible, but the way pgvector
structures the SQL files forbids installing 0.7.4 if you have a 0.8.0
distribution. Yet, some users may need a previous version for backward
compatibility, e.g., restoring the dump.
See this thread for discussion
https://neondb.slack.com/archives/C04DGM6SMTM/p1735911490242919?thread_ts=1731343604.259169&cid=C04DGM6SMTM
## Summary of changes
Put `vector--0.7.4.sql` file into compute image to allow installing this
version as well.
Tested on staging and it seems to be working as expected:
```sql
select * from pg_available_extensions where name = 'vector';
name | default_version | installed_version | comment
--------+-----------------+-------------------+------------------------------------------------------
vector | 0.8.0 | (null) | vector data type and ivfflat and hnsw access methods
create extension vector version '0.7.4';
select * from pg_available_extensions where name = 'vector';
name | default_version | installed_version | comment
--------+-----------------+-------------------+------------------------------------------------------
vector | 0.8.0 | 0.7.4 | vector data type and ivfflat and hnsw access methods
alter extension vector update;
select * from pg_available_extensions where name = 'vector';
name | default_version | installed_version | comment
--------+-----------------+-------------------+------------------------------------------------------
vector | 0.8.0 | 0.8.0 | vector data type and ivfflat and hnsw access methods
drop extension vector;
create extension vector;
select * from pg_available_extensions where name = 'vector';
name | default_version | installed_version | comment
--------+-----------------+-------------------+------------------------------------------------------
vector | 0.8.0 | 0.8.0 | vector data type and ivfflat and hnsw access methods
```
If we find out it's a good approach, we can adopt the same for other
extensions with a stable ABI -- support both `current` and `current - 1`
releases.
Seems nice to keep all these together. This also provides a nice place
for a README file to describe the compute image build process. For
now, it briefly describes the contents of the directory, but can be
expanded.
