Update for jsonb compression

use-timescale/hypercore/compression-methods.md

@@ -279,6 +279,32 @@ have a lot of repeated values, then the dictionary is the same size as the
 original data. TimescaleDB automatically detects this case, and falls back to
 not using a dictionary in that scenario.
 
+#### JSONB compression
+
+For JSONB columns, TimescaleDB uses a two-layer compression approach:
+
+1. **TimescaleDB dictionary compression**: First, TimescaleDB attempts to apply
+   its own dictionary compression to the JSONB data. This works well when JSONB
+   values have high repetition.
+
+2. **PostgreSQL TOAST compression**: If dictionary compression doesn't perform
+   well (for example, when each JSONB value is unique or nearly unique),
+   TimescaleDB skips compression and allows PostgreSQL to handle the data using
+   its TOAST (The Oversized-Attribute Storage Technique) compression. By default,
+   PostgreSQL uses `pglz` compression, but this can be configured to use more
+   modern compression algorithms like `lz4` by setting the `default_toast_compression`
+   configuration parameter.
+
+You can check your current TOAST compression setting:
+
+```sql
+SHOW default_toast_compression;
+```
+
+This two-layer approach ensures that JSONB data is compressed efficiently
+regardless of its characteristics, using dictionary compression when beneficial
+and falling back to LZ-based compression when dictionary compression is not effective.
+
 [decompress-chunks]: /use-timescale/:currentVersion:/compression/decompress-chunks
 [manual-compression]: /use-timescale/:currentVersion:/compression/manual-compression/
 [delta]: /use-timescale/:currentVersion:/hypercore/compression-methods/#delta-encoding