ircd::db: Add compression string option to column descriptor.

include/ircd/db/descriptor.h

@@ -75,6 +75,11 @@ struct ircd::db::descriptor
 	/// the cache.
 	size_t meta_block_size { 512 };
 
+	/// Compression algorithm for this column. Empty string is equal to
+	/// kNoCompression. List is semicolon separated to allow fallbacks in
+	/// case the first algorithms are not supported.
+	std::string compression {"kSnappyCompression;kLZ4Compression"};
+
 	/// User given compaction callback surface.
 	db::compactor compactor {};
 };

ircd/db.cc

@@ -1627,8 +1627,7 @@ ircd::db::database::column::column(database &d,
 	this->options.optimize_filters_for_hits = this->descriptor->expect_queries_hit;
 
 	// Compression
-	//TODO: descriptor / conf / detect etc...
-	this->options.compression = rocksdb::kSnappyCompression;
+	this->options.compression = find_supported_compression(this->descriptor->compression);
 	//this->options.compression = rocksdb::kNoCompression;
 
 	//TODO: descriptor / conf
@@ -9603,6 +9602,29 @@ const
 // Misc
 //
 
+rocksdb::CompressionType
+ircd::db::find_supported_compression(const std::string &list)
+{
+	rocksdb::CompressionType ret
+	{
+		rocksdb::kNoCompression
+	};
+
+	tokens(list, ';', [&ret]
+	(const string_view &name)
+	{
+		for(size_t i(0); i < db::compressions.size(); ++i)
+			if(!db::compressions.at(i).empty())
+				if(name == db::compressions.at(i))
+				{
+					ret = rocksdb::CompressionType(i);
+					break;
+				}
+	});
+
+	return ret;
+}
+
 rocksdb::DBOptions
 ircd::db::make_dbopts(std::string optstr,
                       std::string *const &out,

ircd/db.h

@@ -76,6 +76,7 @@ namespace ircd::db
 	// Database options creator
 	bool optstr_find_and_remove(std::string &optstr, const std::string &what);
 	rocksdb::DBOptions make_dbopts(std::string optstr, std::string *const &out = nullptr, bool *read_only = nullptr, bool *fsck = nullptr);
+	rocksdb::CompressionType find_supported_compression(const std::string &);
 
 	// Validation functors
 	bool valid(const rocksdb::Iterator &);