Add note on expire value effect on history gaps

doc/modules/history_redis.md

@@ -9,30 +9,32 @@ The purpose of this module is to enable the storage of history in Redis lists wi
 
 ## Storage model
 
-This module stores keys as following:
+This module stores keys as follows:
 
 1. Get key prefix
 2. Append hostname
 3. Append `_zst` if history is compressed
 
-In addition, there is a special set where suffixes are stored, and the keyname for this set is simply `key_prefix`. For example, if there is a host `example.local` and it stores compressed history entries then it will save the following element if `key_prefix` set: `example.local_zst`.
+In addition, there is a special set where suffixes are stored, and the keyname for this set is simply `key_prefix`. For example, if there is a host `example.local` and it stores compressed history entries, it will save the following element if `key_prefix` is set: `example.local_zst`.
 
 ## Compression
 
 Rspamd uses [zstd](https://facebook.github.io/zstd/) compression, which is highly efficient for both compression and decompression, offering a typical compression rate of 50% for history elements. As long as you have sufficient computational power, it is recommended to use zstd in order to minimize Redis memory usage when storing elements.
 
 ## WebUI support
 
-Web Interface automatically recognises that history is stored in Redis and load it appropriately.
+The Web Interface automatically recognises that history is stored in Redis and loads it appropriately.
 
 ## Configuration
 
-The configuration of this module is pretty straightforward (use `local.d/history_redis.conf` to define your own values:
+The configuration of this module is pretty straightforward (use `local.d/history_redis.conf` to define your own values):
 
 ~~~hcl
 servers = 127.0.0.1:6379; # Redis server to store history
 expire = 432000; # Expire in seconds for inactive keys, default to 5 days
 nrows = 200; # Default rows limit
 compress = true; # Use zstd compression when storing data in Redis
-subject_privacy = false; # subject privacy is off
+subject_privacy = false; # Subject privacy is off
 ~~~
+
+**Note:** Reducing the `expire` value can result in a one-time situation where newer entries are deleted before older ones, creating a gap in the middle of the history.