wal-g: Support setting the compression method.

docs/production/system-configuration.md

@@ -296,6 +296,13 @@ value. Also supported is "[S3 Reduced Redundancy][s3-rr]", by setting
 [s3-ia]: https://aws.amazon.com/s3/storage-classes/#Infrequent_access
 [s3-rr]: https://aws.amazon.com/s3/reduced-redundancy/
 
+#### `backups_compression_method`
+
+What compression method to use when storing backups; defaults to `lz4`, which is
+fast but does not compress particularly well. Other options are `lzma`, `zstd`,
+and `brotl`; `lzma` provides the best (and slowest) compression, while `zstd`
+and `brotli` are middling compromises.
+
 #### `missing_dictionaries`
 
 If set to a true value during initial database creation, uses PostgreSQL's

puppet/zulip/files/postgresql/env-wal-g

@@ -8,6 +8,9 @@ export PGHOST=/var/run/postgresql/
 WALG_DELTA_MAX_STEPS=$(crudini --get /etc/zulip/zulip.conf postgresql backups_incremental 2>/dev/null)
 export WALG_DELTA_MAX_STEPS
 
+WALG_COMPRESSION_METHOD=$(crudini --get /etc/zulip/zulip.conf postgresql backups_compression_method 2>/dev/null)
+export WALG_COMPRESSION_METHOD
+
 s3_backups_bucket=$(crudini --get "$ZULIP_SECRETS_CONF" secrets s3_backups_bucket 2>/dev/null)
 
 if [ "$s3_backups_bucket" != "" ] || [ -n "$WALG_S3_PREFIX" ]; then