โ11-27-2023 07:18 PM
Hi,
Is it possible to convert existing delta table with partition having data to clustering? If so can you please suggest the steps required? I tried and searched but couldn't find any. Is it that liquid clustering can be done only for new Delta tables? Please help
โ11-27-2023 11:52 PM
Hi @techuser, Certainly! Converting an existing Delta table with partition to a Delta table with clustering is possible. Hereโs a recommended approach:
Backup Table A: Create a backup of your original table (Table A) as A_bkp. This ensures you have a copy of the data before making changes.
Create a New Delta Table: Replace or drop the existing Table A and create a new Delta table with the desired clustering column (Column B). You can use the following SQL command to create the new table:
CREATE TABLE Table_A
USING DELTA
CLUSTERED BY (Column_B)
AS SELECT * FROM A_bkp;
Replace Column_B
with the actual name of the column you want to use for clustering.
Insert Data: Insert data from the backup table (A_bkp) into the newly created Table A:
INSERT INTO Table_A
SELECT * FROM A_bkp;
Cleanup: Finally, drop the backup table (A_bkp) and remove any associated files.
This approach allows you to transition from partitioning to clustering without losing data. Remember to thoroughly test the process in a non-production environment before applying it to your actual data. Additionally, ensure that the new clustering column is appropriate for your use case and query patte...
โ11-27-2023 08:01 PM
Hi @techuser, Certainly! Liquid clustering is a powerful feature in Delta Lake that allows you to optimize data layout without rewriting existing data. It replaces traditional table partitioning and ZORDER, making it easier to manage data and improve query performance.
Let me guide you through the steps:
Enable Liquid Clustering:
Incrementally Cluster Data:
Changing Clustering Keys:
Compatibility and Limitations:
Remember that liquid clustering is recommended for new Delta tables, but you can also apply it to existing tables. Happy clustering! ๐
For more details, refer to the official Databricks documentation on liquid clustering.
โ11-27-2023 09:57 PM - edited โ11-27-2023 10:07 PM
@Kaniz_Fatma How this can be applied to existing delta table which is partitioned having data? Can you please suggest me the steps involved? The existing delta table is partitioned and hence the location files are all partitioned. So is it possible to convert this to cluster? In existing databricks documentation, its mentioned for NEW tables.
โ11-27-2023 10:18 PM
Hi @techuser, Certainly! If you have an existing Delta table that is partitioned and you want to change the partition column, you can follow these steps:
Read the Current Table:
spark.read.table("mytable")
, where "mytable"
is the name of your table.Overwrite the Contents and Schema:
val input = spark.read.table("mytable")
input.write.format("delta")
.mode("overwrite")
.option("overwriteSchema", "true")
.partitionBy("new_partition_column") // Specify the new partition column
.saveAsTable("mytable")
Replace "new_partition_column"
with the name of the new partition column you want to use.Explanation:
Additional Notes:
ALTER TABLE
command with CLUSTER ...
Remember to replace "mytable"
and "new_partition_column"
with your actual table name and desired partition column. Happy data wrangling! ๐
โ11-27-2023 10:26 PM
Hi,
Sorry for again asking this. My requirement is not to change partition column for existing Delta table. My requirement is to change the existing delta table example Table A partitioned by Column 1, Column 2 to Table A cluster by Column 3.
Requirement is converting existing partitioned Delta table to Delta table with cluster with new column.
โ11-27-2023 10:30 PM
Hi @techuser, To convert an existing partitioned Delta table to a Delta table clustered by a new column, you can use the CONVERT TO DELTA
command in Databricks SQL.
Hereโs how you can achieve this:
Read the existing table: First, read the current partitioned Delta table (letโs call it โmytableโ) using Spark:
val input = spark.read.table("mytable")
Overwrite the contents and schema: Overwrite the table's contents and schema. Set the overwriteSchema
option to true
To ensure that the schema is updated:
input.write
.format("delta")
.mode("overwrite")
.option("overwriteSchema", "true")
Cluster by the new column: Specify the new column (letโs say โcolBโ) by which you want to cluster the table:
.partitionBy("colB") // Specify the new column for clustering
.saveAsTable("mytable") // Save the updated table
This process will convert your existing partitioned Delta table into a Delta table clustered by the specified new column. Remember to adjust the column names and table names according to your use case.
Keep in mind the following caveats:
VACUUM
operation.Happy clustering! ๐๐
โ11-27-2023 10:48 PM
While defining a new table which uses liquid cluster, we mention at the end as 'USING DELTA CLUSTER BY (Column1)'
As per above solution Point 3 Cluster by the new column, its mentioned as
.partitionBy("colB")
How is it identified as CLUSTER? Because while creating a table we have CLUSTER BY and PARTITION BY as 2 different usage and that's how table is identified as CLUSTER or PARTITION.
As per above explanation , does the DESCRIBE table show it as cluster?
โ11-27-2023 11:05 PM
Hi @techuser , When defining a new table that utilizes liquid clustering in Delta Lake, we specify the clustering key using the USING DELTA CLUSTER BY (Column1) syntax.
However, it seems there might be some confusion regarding the distinction between clustering and partitioning.
Letโs break it down:
Clustering:
Partitioning:
DESCRIBE Table:
In summary, while the DESCRIBE command wonโt directly show whether a table is clustered using liquid clustering, you can infer it from the table creation statement and the presence of the CLUSTER BY clause. Liquid clustering enhances query performance and provides flexibility, making it a recommended choice for new Delta tables.
โ11-27-2023 11:36 PM
Thank you for the response!
DESCRIBE table gives the column and datatype details and also the columns of PARTITION and CLUSTER. If cluster is used it mentions as Clustering Information and mention the columns used likewise for partition also.
So back to my previous question. Is there a way to Convert existing Delta Table with partition to a Delta Table with cluster.
1. Table A -- Partition column A
2. Take back up of Table A as A_bkp
3. Replace or Drop/Create Table A with Cluster Column B
4. INSERT TABLE A AS SELECT * FROM A_BKP
5. DROP A_BKP, remove the files associated
Is this a good approach?
โ11-27-2023 11:52 PM
Hi @techuser, Certainly! Converting an existing Delta table with partition to a Delta table with clustering is possible. Hereโs a recommended approach:
Backup Table A: Create a backup of your original table (Table A) as A_bkp. This ensures you have a copy of the data before making changes.
Create a New Delta Table: Replace or drop the existing Table A and create a new Delta table with the desired clustering column (Column B). You can use the following SQL command to create the new table:
CREATE TABLE Table_A
USING DELTA
CLUSTERED BY (Column_B)
AS SELECT * FROM A_bkp;
Replace Column_B
with the actual name of the column you want to use for clustering.
Insert Data: Insert data from the backup table (A_bkp) into the newly created Table A:
INSERT INTO Table_A
SELECT * FROM A_bkp;
Cleanup: Finally, drop the backup table (A_bkp) and remove any associated files.
This approach allows you to transition from partitioning to clustering without losing data. Remember to thoroughly test the process in a non-production environment before applying it to your actual data. Additionally, ensure that the new clustering column is appropriate for your use case and query patte...
โ04-08-2024 05:13 AM
Does Liquid Clustering accepts Merge or How Upsert can be done efficiently with Liquid clustered delta table
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