The HASH function ensures that rows will be distributed mostly evenly in all the partition table. Each partition will hold the rows for which the hash value of the partition key divided by the specified modulus will produce the specified remainder. The table is partitioned by specifying a modulus and a remainder for each partition. Hash partitioning solves this data distribution issue. It is a new partition mechanism, if you can not decide on a range or list partition (as you are not sure how big the bucket would be). There cannot be more than one DEFAULT table for partition table. Severalnines_v11=# CREATE TABLE customer_usa PARTITION OF customers FOR VALUES IN ('USA') ĭEFAULT partition cannot be specified for HASH partitioned table. Severalnines_v11=# DELETE FROM customers_def WHERE cust_country in ('USA') DELETE 1 Resolution - You need to move/remove those rows from Default table, then it will then let you create new part table like below. 00:46:34.890 IST STATEMENT: CREATE TABLE customer_usa PARTITION OF customers FOR VALUES IN ('USA') ERROR: updated partition constraint for default partition "customers_def" would be violated by some row 00:46:34.890 IST ERROR: updated partition constraint for default partition "customers_def" would be violated by some row severalnines_v11=# CREATE TABLE customer_usa PARTITION OF customers FOR VALUES IN ('USA') In this case `USA` existed in Default partition so it won’t work like below. Word of caution: Default partition will prevent any new partition addition if that partition value exists in the default table. Severalnines_v11=# select * FROM customers_def Severalnines_v11=# INSERT INTO customers VALUES (4499,'Tony','Arizona','USA') CREATE TABLE customers_def PARTITION OF customers DEFAULT Lab Example: `USA` country code was not defined in the partition table below, but still it gets inserted in the default table successfully. A row that is not mapped to any partition table would be inserted in the default partition. Prior to PostgreSQL 11, these rows would error out. The PostgreSQL 11 DEFAULT partition feature stores tuples that don’t map to any other partition. 00:13:54.901 IST STATEMENT: UPDATE customers1 SET cust_country ='ypp' WHERE cust_id=2039 ĮRROR: no partition of relation "customers1" found for rowĭETAIL: Partition key of the failing row contains (cust_country) = (ypp). 00:13:54.901 IST DETAIL: Partition key of the failing row contains (cust_country) = (ypp). 00:13:54.901 IST ERROR: no partition of relation "customers1" found for row severalnines_v11=# UPDATE customers1 SET cust_country ='ypp' WHERE cust_id=2039 (0 rows) severalnines_v11=# SELECT * FROM customer_jap Ĭaution: The UPDATE will error out, if there is no default partition table and updated values doesn’t match with partition criteria in any child table. severalnines_v11=# SELECT * FROM customer_ind it moved the row to correct partition table. (1 row) severalnines_v11=# UPDATE customers SET cust_country ='jap' WHERE cust_id=2039 INSERT 0 1 severalnines_v11=# SELECT * FROM customer_ind Ĭust_id | cust_name | cust_address | cust_country CREATE TABLE customers(cust_id bigint NOT NULL,cust_name varchar(32) NOT NULL,cust_address text,Ĭust_country text)PARTITION BY LIST(cust_country) ĬREATE TABLE customer_ind PARTITION OF customers FOR VALUES IN ('ind') ĬREATE TABLE customer_jap PARTITION OF customers FOR VALUES IN ('jap') ĬREATE TABLE customers_def PARTITION OF customers DEFAULT severalnines_v11=# INSERT INTO customers VALUES (2039,'Puja','Hyderabad','ind') Create a table and verify how the update works on partition key. Under the hood it basically executes DELETE FROM old partition and INSERT into new partition ( DELETE + INSERT).Īlright, let’s test this out. Update statement can change the value of partition key it actually moves the rows to the correct partition table. Prior to PostgreSQL 11, Update statement that changes the value of partition key was restricted and not allowed. The details of these new partitioning features will be covered in this blog with a few code examples. With the recent release of PostgreSQL 11 there are a lot of new amazing partitioning features. You can read more about PostgreSQL partitioning in our blog “ A Guide to Partitioning Data In PostgreSQL”. Partitioning splits large tables into smaller pieces, which helps with increasing query performance, making maintenance tasks easier, improving the efficiency of data archival, and faster database backups.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |