[FIX] base: replace useless vat index with regular one

The custom vat index name matched the name that the system uses for automatic
indexes (when a field has `index=True`).

But the `vat` field  was created with `index=False`, and this means that the
ORM would execute a `DROP INDEX IF EXISTS res_partner_vat_index` when updating
any addon that touches the `res.partner` model. Since this model is so
ubiquitous, this resulted in a ton of unnecessary `DROP INDEX` + `CREATE INDEX`
queries when updating any database.

What's even worse is that dropping or creating an index needs a complete
semaphore lock of the whole table, so if you're updating a high-traffic HA
production instance while it is running, you have a very high rate of concurrency
failures, because almost everybody is going to be using the `res.partner` model
in some way almost all the time.

A deeper investigation reveals that the index itself was useless. It was added in
a6e1eb9 and apparently meant to be used for optimizing name_search(). But even
though a6e1eb9 modified name_search(), it did the substitution in Python[1], so
in practice the database had no way to recognize the pattern and never used the
index. The specificity of that index makes it useless for other cases too, so it
can simply be dropped to save space.

Further, considering that the `vat` field is a common search criterion, it
actually makes sense to enable a normal index on that field, by setting
`index=True`. Neither dropping the index nor creating the default one has any
impact on existing databases, so it's safe in a stable series. A new
installation or a forced update will be necessary to benefit from the changes.

~~Finally, because the bad custom index had the same name as the regular one, an
upgrade script is foreseen to drop the old one before letting the ORM re-create
it properly.~~

Fwd-port note: the upgrade script and version bump were reverted as a
consequence of the unforeseen consequences in #60771.

1: https://github.com/odoo/odoo/blob/a6e1eb9f0ad285fac7d0ca0b9f89f046d78ec9c7/odoo/addons/base/models/res_partner.py#L710

@Tecnativa TT26303

Closes #60346
See also: #60771

closes odoo/odoo#60858

X-original-commit: 2f4a7de3d25cec36ac3b85e3f33122728346c206
Signed-off-by: Olivier Dony (odo) <odo@openerp.com>

0 files changed, 0 insertions, 0 deletions