Behavior of convert_quicklz_to_zstd on Partitioned Tables in Greenplum 6.32

Products

• VMware Tanzu Greenplum

Issue/Introduction

Greenplum Database 6.32 introduces a new option, convert_quicklz_to_zstd, for the ALTER TABLE … SET WITH (REORGANIZE=true) command. This option allows append-optimized tables to convert data compressed with QuickLZ to Zstd.
The conversion supports both table-level and column-level compression.

This KB focuses on the behavior of this option when it is applied to a partitioned table, where child partitions may use different compression types, and the option is set on the root (parent) table.

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Scenario

• A partitioned append-optimized table exists.

• Child partitions use different compression settings:

  • Some partitions use quicklz

  • Some use other compression types (for example, zlib)

  • Some have no compression

• The convert_quicklz_to_zstd=true option is applied at the root table level using ALTER TABLE … SET WITH (REORGANIZE=true).

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Expected Behavior

When convert_quicklz_to_zstd=true is applied to the root partitioned table:

1. Only partitions using QuickLZ compression are converted to Zstd.

2. Partitions using other compression types (or no compression) remain unchanged.

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Example

Table Definition

CREATE TABLE sales (id int, date date, amt decimal) 
WITH (appendoptimized=true, orientation=column) 
DISTRIBUTED BY (id)
PARTITION BY RANGE (date) (
    -- Partition 1: QuickLZ
    PARTITION p1 START ('2023-01-01'::date) END ('2023-02-01'::date) 
    WITH (appendoptimized=true, orientation=column, compresstype=quicklz, compresslevel=1),
    
    -- Partition 2: ZLIB
    PARTITION p2 START ('2023-02-01'::date) END ('2023-03-01'::date) 
    WITH (appendoptimized=true, orientation=column, compresstype=zlib, compresslevel=5),
    
    -- Partition 3: No Compression
    PARTITION p3 START ('2023-03-01'::date) END ('2023-04-01'::date)
    WITH (appendoptimized=true, orientation=column, compresstype=none)
);

Apply Compression Conversion on Root Table

ALTER TABLE sales 
SET WITH (
    REORGANIZE=true, 
    convert_quicklz_to_zstd=true
);

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Result

After the operation completes:

• Partition p1 is converted from quicklz to zstd

• Partition p2 (zlib) is unchanged

• Partition p3 (none) is unchanged

Verification example:

for i in `seq 1 3`; do 
  echo -n "sales_1_prt_p${i}: "; 
  psql -c "\d+ sales_1_prt_p$i" | grep Options; 
done

Output:

sales_1_prt_p1: Options: appendonly=true, orientation=column, compresstype=zstd, compresslevel=1
sales_1_prt_p2: Options: appendonly=true, orientation=column, compresstype=zlib, compresslevel=5
sales_1_prt_p3: Options: appendonly=true, orientation=column, compresstype=none

 

Resolution

Summary

When convert_quicklz_to_zstd=true is executed on a partitioned table:

• The conversion is selective.

• Only partitions using QuickLZ are affected.

• Other compression types and uncompressed partitions are not modified.

This behavior allows safe execution of the conversion on mixed-compression partitioned tables without impacting non-QuickLZ partitions.