diff --git a/src/sdsdkv-client.h b/src/sdsdkv-client.h
index 2f8156c..a681670 100644
--- a/src/sdsdkv-client.h
+++ b/src/sdsdkv-client.h
@@ -140,7 +140,8 @@ struct sdsdkv_client : public personality {
         //
         ch_placement_find_closest(
             m_place,
-            // TODO(skg) How to properly handle arbitrary data?
+            // TODO(skg) How to properly handle arbitrary-sized data (e.g., data
+            // less than sizeof(uint64_t))?
             *(uint64_t *)(key),
             replication,
             server_indices
diff --git a/src/sdsdkv-config.h b/src/sdsdkv-config.h
index c10308d..b1df95c 100644
--- a/src/sdsdkv-config.h
+++ b/src/sdsdkv-config.h
@@ -62,6 +62,8 @@ class sdsdkv_iconfig {
     //
     sdsdkv_config_db db_type;
     //
+    sdsdkv_compare_fn cmp_fn;
+    //
     std::string group_name;
     //
     std::string db_path;
@@ -88,6 +90,7 @@ class sdsdkv_iconfig {
         personality = config.personality;
         hash_be = config.hash_be;
         db_type = config.db_type;
+        cmp_fn = config.cmp_fn;
         group_name = string(config.group_name);
         db_path = string(config.db_path);
         db_name = string(config.db_name);
diff --git a/src/sdsdkv-server.h b/src/sdsdkv-server.h
index 4609ed6..0fdad09 100644
--- a/src/sdsdkv-server.h
+++ b/src/sdsdkv-server.h
@@ -122,8 +122,7 @@ struct sdsdkv_server : public personality {
                      m_config->db_name.c_str(),
                      m_config->db_path.c_str(),
                      sdsdkv_iconfig::get_real_db_type(m_config->db_type),
-                     // TODO(skg) Make a user param.
-                     SDSKV_COMPARE_DEFAULT,
+                     m_config->cmp_fn,
                      &m_dbid
                  );
         if (rc != SDSKV_SUCCESS) return sdskv2irc(rc);
diff --git a/src/sdsdkv.h b/src/sdsdkv.h
index 3b8e4a8..368070e 100644
--- a/src/sdsdkv.h
+++ b/src/sdsdkv.h
@@ -24,6 +24,12 @@ extern "C" {
 /** Convenience definition (in case anyone needs this). */
 #define SDSDKV 1
 
+/** Default comparison function type. */
+#define SDSDKV_COMPARE_DEFAULT NULL
+
+/** Custom comparison function type. */
+typedef int (*sdsdkv_compare_fn)(const void*, size_t, const void*, size_t);
+
 /** External context type. */
 typedef void* sdsdkv_context;
 
@@ -97,6 +103,7 @@ enum sdsdkv_config_db {
     SDSDKV_DB_LEVELDB
 };
 
+
 // TODO(skg) Allow for two modes of operation:
 // - Total lash-up
 // - Connect
@@ -111,6 +118,8 @@ typedef struct sdsdkv_config {
     sdsdkv_config_hashing hash_be;
     /** Database type. */
     sdsdkv_config_db db_type;
+    /** Key comparison function. */
+    sdsdkv_compare_fn cmp_fn;
     /** Group name. */
     char *group_name;
     /** If applicable, the path where database files will be written. */
diff --git a/tests/trivial.cc b/tests/trivial.cc
index c7a2987..e9eb118 100644
--- a/tests/trivial.cc
+++ b/tests/trivial.cc
@@ -54,11 +54,13 @@ main(int argc, char **argv)
         /* .init_comm = */
         MPI_COMM_WORLD,
         /* .personality = */
-        (rank == 0) ? SDSDKV_PERSONALITY_SERVER: SDSDKV_PERSONALITY_CLIENT,
+        (rank == 0) ? SDSDKV_PERSONALITY_SERVER : SDSDKV_PERSONALITY_CLIENT,
         /* .hash_be = */
         SDSDKV_HASHING_CH_PLACEMENT,
         /* .db_type = */
         SDSDKV_DB_LEVELDB,
+        /* .cmp_fn= */
+        SDSDKV_COMPARE_DEFAULT,
         /* .group_name = */
         (char *)"groupname",
         /* .db_path = */