Enable range statistics for a specific column in a compressed hypertable. This tracks a range of values for that column per chunk. Used for chunk pruning during query optimization.
| Name | Type | Description |
|---|---|---|
hypertable | REGCLASS | Hypertable that the column belongs to |
column_name | TEXT | Column to track range statistics for |
| Name | Type | Description |
|---|---|---|
if_not_exists | BOOLEAN | Set to true so that a notice is sent when ranges are not being tracked for a column. By default, an error is thrown |
| Column | Type | Description |
|---|---|---|
column_stats_id | INTEGER | ID of the entry in the TimescaleDB internal catalog |
enabled | BOOLEAN | Returns true when tracking is enabled, if_not_exists is true, and when a new entry is not |
| added |
Note
TimescaleDB supports min/max range tracking for the smallint, int, bigint, serial, bigserial, date, timestamp, and timestamptz data types.
In this sample, you convert the conditions table to a hypertable with
partitioning on the time column. You then specify and enable additional columns to track ranges for.
SELECT create_hypertable('conditions', 'time');SELECT enable_chunk_skipping('conditions', 'device_id');
Note
Best practice is to enable range tracking on columns that are correlated to the partitioning column. In other words, enable tracking on secondary columns which are referenced in the WHERE clauses in your queries.
The min/max ranges are calculated when a chunk belonging to
this hypertable is compressed using the compress_chunk function.
The range is stored in start (inclusive) and end (exclusive) form in the
chunk_column_stats catalog table.
This way you store the min/max values for such columns in this catalog
table at the per-chunk level. These min/max range values do
not participate in partitioning of the data. These ranges are
used for chunk pruning when the WHERE clause of an SQL query specifies
ranges on the column.
A DROP COLUMN on a column with statistics tracking enabled on it ends up removing all relevant entries from the catalog table.
A decompress_chunk invocation on a compressed chunk resets its entries
from the chunk_column_stats catalog table since now it's available for DML and the
min/max range values can change on any further data manipulation in the chunk.
Keywords
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