Basically there are 4 steps:
Rename old table
Create new table
with partitioning
Add constraint on old table for it's proposed partition ranges
Attach old table as a partition to new partition table
Sounds easy right?
What about indexes? What about Triggers?
And guess what, there are other traps to watch out for!
-- Add the check constraint
alter table public.test_partition_10_25 add constraint test_partition_10_25_constraint CHECK (id >= 10 AND id <25) NOT VALID;
update pg_constraint pgc
SET convalidated = true
FROM pg_class c
WHERE
c.oid = pgc.conrelid
AND connamespace = 'public'::regnamespace::oid
AND c.relname = 'test_partition_10_25'
AND conname = 'test_partition_10_25_constraint';
pgloader will keep a separate file of rejected data, but continue trying to copy good data in your database.
pgloader also implements data reformatting, a typical example of that being the transformation of MySQL datestamps 0000-00-00 and 0000-00-00 00:00:00 to PostgreSQL NULL value
@Repository
public interface PostRepository extends BaseJpaRepository<Post, Long> {
@Query("""
select p
from Post p
where date(p.createdOn) >= :sinceDate
"""
)
@QueryHints(
@QueryHint(name = AvailableHints.HINT_FETCH_SIZE, value = "25")
)
Stream<Post> streamByCreatedOnSince(@Param("sinceDate") LocalDate sinceDate);
}
The FETCH_SIZE JPA query hint is necessary for PostgreSQL and MySQL to instruct the JDBC Driver to prefetch at most 25 records. Otherwise, the PostgreSQL and MySQL JDBC Drivers would prefetch all the query results prior to traversing the underlying ResultSet.
Postgres allows:
UPDATE dummy
SET customer=subquery.customer,
address=subquery.address,
partn=subquery.partn
FROM (SELECT address_id, customer, address, partn
FROM /* big hairy SQL */ ...) AS subquery
WHERE dummy.address_id=subquery.address_id;
This syntax is not standard SQL
Currently adding a column to a table with a non-NULL default results in
a rewrite of the table. For large tables this can be both expensive and
disruptive. This patch removes the need for the rewrite as long as the
default value is not volatile. The default expression is evaluated at
the time of the ALTER TABLE and the result stored in a new column
(attmissingval) in pg_attribute, and a new column (atthasmissing) is set
to true. Any existing row when fetched will be supplied with the
attmissingval. New rows will have the supplied value or the default and
so will never need the attmissingval.
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CREATE TABLE books (
book_id serial NOT NULL,
data jsonb
);
INSERT INTO books VALUES (1, '{"title": "Sleeping Beauties", "genres": ["Fiction", "Thriller", "Horror"], "published": false}');
SELECT data->'title' AS title FROM books WHERE data->'published' = 'false';
CREATE INDEX idx_published ON books ((data->'published'));
select * from tbl TABLESAMPLE system (5)
The SYSTEM method is significantly faster than the BERNOULLI method when small sampling percentages are specified, but it may return a less-random sample of the table as a result of clustering effects.
SELECT * FROM pg_stat_activity WHERE state = 'active';
So you can identify the PID of the hanging query you want to terminate, run this:
SELECT pg_cancel_backend(PID);
Execute one command (or mount one Node.js middleware) and get an instant high-performance GraphQL API for your PostgreSQL database! - graphile/postgraphile
-- show running queries (9.2)
SELECT pid, age(clock_timestamp(), query_start), usename, query
FROM pg_stat_activity
WHERE query != '<IDLE>' AND query NOT ILIKE '%pg_stat_activity%'
ORDER BY query_start desc;
Partial Indexes
A partial index is an index built over a subset of a table; the subset is defined by a conditional expression (called the predicate of the partial index). The index contains entries for only those table rows that satisfy the predicate.
CREATE INDEX access_log_client_ip_ix ON access_log (client_ip)
WHERE NOT (client_ip > inet '192.168.100.0' AND client_ip < inet '192.168.100.255');
As a database developer, you want these sub-transactions or autonomous transactions to be processed and committed regardless of what happens to the larger surrounding transaction block.
The pg_background Postgres extension originally written by Robert Haas starts a separate worker to process a SQL statement, which is a nice way to achieve an autonomous transaction.
Sequelize is a promise-based ORM for Node.js and io.js. It supports the dialects PostgreSQL, MySQL, MariaDB, SQLite and MSSQL and features solid transaction support, relations, read replication and more.
Objection.js is an ORM for Node.js that aims to stay out of your way and make it as easy as possible to use the full power of SQL and the underlying database engine while keeping magic to a minimum.