by My application is gathering personel and patient data for a hospice. It must
keep track of all changes to patient stats, chart, and med sheet over time.
Therefore, I would like to keep versions of the rows in many of my tables.
This is my stab at a PostgreSQL implementation. I would greatly appreciate any
input, criticisms, dire warnings, etc.
I plan on adding a transaction table with a transaction_id column fed by a
sequence. The transaction_id will indicate the order of creation as well as
time of creation.
-- A row for each of our customers who subscribe to the application.
create table firm ( -- firm => hospice, clinic, hospital
firm_id integer not null,
name varchar(32), -- Just one example data column
primary key (firm_id)
)
\g
-- A table to keep row of a transaction.
create table transaction (
firm_id integer not null,
transaction_id integer not null, -- Fed by sequence, one for each firm so
-- we can part and merge databases by
-- firm without collision!
modified timestamp not null,
modified_by person_id not null,
primary key (firm_id, transaction_id),
foreign key (firm_id) references firm
)
\g
-- Example versioned table.
create table person_history ( -- Base for patient and employee
firm_id integer not null,
person_id integer not null,
transaction_id integer not null,
first_name varchar(32), -- Just two example data columns
last_name varchar(32) not null,
deleted boolean not null,
primary key (firm_id, person_id, transaction_id)
)
\g
-- Show latest row view.
create view person as
select *
from person_history
where transaction_id = ( -- In explain this subselect appears to use index!
select max(transaction_id)
from person_history as ph1
where firm_id = ph1.firm_id
and person_id = ph1.firm_id
)
and deleted = 0
\g
-- Time travel view.
create view person_as_of as
select *
from person_history
where transction_id = (
select max(transaction_id)
from person_history as ph1
where firm_id = ph1.firm_id
and person_id = ph1.firm_id
and transaction_id <= (
select transaction_id
from past_transaction
limit 1
)
)
and deleted = 0
\g
In my application I can travel in time thus:
create temporary table past_transaction as
select transaction_id
from transaction
where modified <= '2002/12/2 17:59:00' -- the minute I turned 31
order by firm_id desc, transaction_id desc,
limit 1
\g
-- If only I could pass the view a parameter!
select * from person_as_of
\g
Thoughts:
* I can write a query and have it travel back in time by setting one variable.
Neeto.
* No archive tables or such means no copying, new version is a simple insert.
Good.
* With expliain the sub selects appear to use the indexes with aggregates, and
if not I can alsways sort descending limit 1. Good.
* Even with complex joins on the latest view tables the query plans use
the primary index for the sub select. Good.
* There is little need for vacuuming, since no updates are made to the
busy tables of the application. Does this matter?
* Referenital integrity goes away from what I can see, since it won't
understand the deleted column. Pity.
Questions:
* Is this viable or overly clever?
* Should I have a boolean latest column on a versioned table? This would mean
update and vacuum, but potentially a faster query.
* Is there a penalty for long (how do you say?) concatenated keys in
PostgreSQL?
* Any reason why this won't work with the coming distrubuted PostgreSQL?
* Where can I read about alternative implemenations for history/versioning?
Nuances?
Thank you all for any input whatsoever.
Alan Gutierrez