Add documentation for hardware-accelerated compression codecs. (#6841)

* Add documentation for hardware-accelerated compression codecs.

Signed-off-by: Mulugeta Mammo <mulugeta.mammo@intel.com>

* Fix based on the review from reviewdog.

Signed-off-by: Mulugeta Mammo <mulugeta.mammo@intel.com>

* Use the registered symbol for Intel and Xeon.

Signed-off-by: mulugetam <mulugeta.mammo@intel.com>

* Minor modifications to the text.

Signed-off-by: mulugetam <mulugeta.mammo@intel.com>

* Rephrasing.

Signed-off-by: mulugetam <mulugeta.mammo@intel.com>

* Paraphrasing.

Signed-off-by: mulugetam <mulugeta.mammo@intel.com>

* Apply suggestions from code review

Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Update _im-plugin/index-codecs.md

Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Update _install-and-configure/configuring-opensearch/index-settings.md

Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

* Apply suggestions from code review

Co-authored-by: Nathan Bower <nbower@amazon.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>

---------

Signed-off-by: Mulugeta Mammo <mulugeta.mammo@intel.com>
Signed-off-by: mulugetam <mulugeta.mammo@intel.com>
Signed-off-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>
Co-authored-by: Naarcha-AWS <97990722+Naarcha-AWS@users.noreply.github.com>
Co-authored-by: Nathan Bower <nbower@amazon.com>

_im-plugin/index-codecs.md

@@ -32,6 +32,26 @@ For the `zstd` and `zstd_no_dict` codecs, you can optionally specify a compressi
 When an index segment is created, it uses the current index codec for compression. If you update the index codec, any segment created after the update will use the new compression algorithm. For specific operation considerations, see [Index codec considerations for index operations](#index-codec-considerations-for-index-operations).
 {: .note}
 
+As of OpenSearch 2.14, hardware-accelerated compression codecs for the `DEFLATE` and `LZ4` compression algorithms are available. These hardware-accelerated codecs are available on the latest 4th and 5th Gen Intel®️ Xeon®️ processors running Linux kernel 3.10 and later. For all other systems and platforms, the codecs use that platform's corresponding software implementations. 
+
+The new hardware-accelerated codecs can be used by setting one of the following `index.codec` values:
+* `qat_lz4` (OpenSearch 2.14 and later): Hardware-accelerated `LZ4`
+* `qat_deflate` (OpenSearch 2.14 and later): Hardware-accelerated `DEFLATE`
+
+`qat_deflate` offers a much better compression ratio than `qat_lz4`, with a modest drop in compression and decompression speed.
+{: .note}
+
+The `index.codec.compression_level` setting can be used to specify the compression level for both `qat_lz4` and `qat_deflate`. 
+
+The `index.codec.qatmode` setting controls the behavior of the hardware accelerator and uses one of the following values:
+
+* `auto`: If hardware acceleration fails, then the algorithm switches to software acceleration.
+* `hardware`: Guarantees hardware-only compression. If hardware is not available, then an exception occurs until hardware exists.
+
+For information about the `index.codec.qatmode` setting's effects on snapshots, see the [Snapshots](#snapshots) section.
+
+For more information about hardware acceleration on Intel, see the [Intel (R) QAT accelerator overview](https://www.intel.com/content/www/us/en/architecture-and-technology/intel-quick-assist-technology-overview.html).
+
 ## Choosing a codec 
 
 The choice of index codec impacts the amount of disk space required to store the index data. Codecs like `best_compression`, `zstd`, and `zstd_no_dict` can achieve higher compression ratios, resulting in smaller index sizes. Conversely, the `default` codec doesn’t prioritize compression ratio, resulting in larger index sizes but faster search operations than `best_compression`.
@@ -58,6 +78,11 @@ When creating a [snapshot]({{site.url}}{{site.baseurl}}/tuning-your-cluster/avai
 
 When you restore the indexes from a snapshot of a cluster to another cluster, it is important to verify that the target cluster supports the codecs of the segments in the source snapshot. For example, if the source snapshot contains segments of the `zstd` or `zstd_no_dict` codecs (introduced in OpenSearch 2.9), you won't be able to restore the snapshot to a cluster that runs on an older OpenSearch version because it doesn't support these codecs. 
 
+For hardware-accelerated compression codecs, available in OpenSearch 2.14 and later, the value of `index.codec.qatmode` affects how snapshots and restores are performed. If the value is `auto` (the default), then snapshots and restores work without issue. However, if the value is `hardware`, then it must be reset to `auto` in order for the restore process to succeed on systems lacking the hardware accelerator.
+
+You can modify the value of `index.codec.qatmode` during the restore process by setting its value as follows: `"index_settings": {"index.codec.qatmode": "auto"}`.
+{: .note}
+
 ### Reindexing
 
 When you are performing a [reindex]({{site.url}}{{site.baseurl}}/im-plugin/reindex-data/) operation from a source index, the new segments created in the target index will have the properties of the codec settings of the target index. 

_install-and-configure/configuring-opensearch/index-settings.md

@@ -79,10 +79,17 @@ OpenSearch supports the following static index-level index settings:
     - `best_compression`
     - `zstd` (OpenSearch 2.9 and later)
     - `zstd_no_dict`(OpenSearch 2.9 and later)
+    - `qat_lz4` (OpenSearch 2.14 and later, on supported systems)
+    - `qat_deflate` (OpenSearch 2.14 and later, on supported systems)
+
+For `zstd`, `zstd_no_dict`, `qat_lz4`, and `qat_deflate`, you can specify the compression level in the `index.codec.compression_level` setting. For more information, see [Index codec settings]({{site.url}}{{site.baseurl}}/im-plugin/index-codecs/). Optional. Default is `default`.
+
+- `index.codec.compression_level` (Integer): The compression level setting provides a trade-off between compression ratio and speed. A higher compression level results in a higher compression ratio (smaller storage size), but slower compression and decompression speeds lead to higher indexing and search latencies. This setting can only be specified if `index.codec` is set to `zstd` and `zstd_no_dict` in OpenSearch 2.9 and later or `qat_lz4` and `qat_deflate` in OpenSearch 2.14 and later. Valid values are integers in the [1, 6] range. For more information, see [Index codec settings]({{site.url}}{{site.baseurl}}/im-plugin/index-codecs/). Optional. Default is 3.
+
+- `index.codec.qatmode` (String): The hardware acceleration mode used for the `qat_lz4` and `qat_deflate` compression codecs. Valid values are `auto` and `hardware`. For more information, see [Index codec settings]({{site.url}}{{site.baseurl}}/im-plugin/index-codecs/). Optional. Default is `auto`. 
+
         
-    For `zstd` and `zstd_no_dict`, you can specify the compression level in the `index.codec.compression_level` setting. For more information, see [Index codec settings]({{site.url}}{{site.baseurl}}/im-plugin/index-codecs/). Optional. Default is `default`.
 
-- `index.codec.compression_level` (Integer): The compression level setting provides a tradeoff between compression ratio and speed. A higher compression level results in a higher compression ratio (smaller storage size) with a tradeoff in speed (slower compression and decompression speeds lead to greater indexing and search latencies). Can only be specified if `index.codec` is set to `zstd` and `zstd_no_dict` compression levels in OpenSearch 2.9 and later. Valid values are integers in the [1, 6] range. For more information, see [Index codec settings]({{site.url}}{{site.baseurl}}/im-plugin/index-codecs/). Optional. Default is 3. 
 
 - `index.routing_partition_size` (Integer): The number of shards a custom routing value can go to. Routing helps an imbalanced cluster by relocating values to a subset of shards rather than a single shard. To enable routing, set this value to greater than 1 but less than `index.number_of_shards`. Default is 1.