cachedb_perf: high-performance local memory cache built on modern kernel features

cachedb/cachedb.h

@@ -162,7 +162,36 @@ typedef struct cachedb_funcs_t {
 	 */
 	int (*is_replicated) (cachedb_con *con);
 
+
 	int capability;
+
+	/**
+	 * OPTIONAL, advertised by CACHEDB_CAP_GET_BUF.  Reads a value into a
+	 * caller-owned buffer, so a hot read path need not allocate: it is
+	 * get() without the pkg_malloc the caller would then have to free.
+	 *
+	 * @buf must be memory private to the calling process (its own stack or
+	 * pkg).  A backend may write into it speculatively and then abandon the
+	 * attempt, so on ANY outcome other than a hit its contents are
+	 * undefined - never a stale previous value to fall back on.  The value
+	 * is not NUL-terminated.
+	 *
+	 * Return values:
+	 *  -3: @buf is too small; *vlen is 0 and *needed holds the size that
+	 *      would be required (the caller may then fall back to get())
+	 *  -2: key does not exist, or has expired
+	 *  -1: internal error, or a malformed request (NULL @buf, or @buflen
+	 *      below the backend's documented minimum)
+	 *   0: found; *vlen bytes were written to @buf, always <= @buflen
+	 *
+	 * *vlen and *needed are zeroed before anything else is done, so a
+	 * caller that ignores the return code reads a zero length rather than
+	 * an uninitialised one.  @needed may be NULL.  NOTE this differs from
+	 * get(), which signals a hit with a positive value at the script
+	 * boundary - a hit here is 0.
+	 */
+	int (*get_buf) (cachedb_con *con, str *attr, char *buf,
+		unsigned int buflen, unsigned int *vlen, unsigned int *needed);
 } cachedb_funcs;
 
 typedef struct cachedb_engines {

cachedb/cachedb_cap.h

@@ -51,8 +51,31 @@ typedef enum {
 	CACHEDB_CAP_MAP_REMOVE   = 1<<13,
 	CACHEDB_CAP_MAP =
 		(CACHEDB_CAP_MAP_GET|CACHEDB_CAP_MAP_SET|CACHEDB_CAP_MAP_REMOVE),
+
+	/* backend implements get_buf() - an allocation-free read into a
+	 * caller-owned buffer.  Optional: every backend still provides get() */
+	CACHEDB_CAP_GET_BUF      = 1<<14,
 } cachedb_cap;
 
+/*
+ * Preprocessor-visible companion to CACHEDB_CAP_GET_BUF.  A consumer cannot test
+ * for the endpoint at runtime alone: get_buf is a struct member, so referencing it
+ * fails to compile against a core that predates it, and the capability above is an
+ * enum constant the preprocessor cannot see.  This lets a module compile against
+ * either core and pick the allocation-free path up automatically:
+ *
+ *   #ifdef CACHEDB_HAVE_GET_BUF
+ *       if (cdbf.get_buf && CACHEDB_CAPABILITY(&cdbf, CACHEDB_CAP_GET_BUF))
+ *           ... use it ...
+ *       else
+ *   #endif
+ *           ... use get() ...
+ *
+ * The runtime half stays necessary: a core may provide the endpoint while the
+ * configured backend does not implement it.
+ */
+#define CACHEDB_HAVE_GET_BUF 1
+
 #define CACHEDB_CAPABILITY(cdbf,cpv) (((cdbf)->capability & (cpv)) == (cpv))
 
 static inline int check_cachedb_api(cachedb_engine *cde)

modules/cachedb_perf/Makefile

@@ -0,0 +1,18 @@
+# cachedb_perf module
+#
+# WARNING: do not run this directly, it should be run by the master Makefile
+
+include ../../Makefile.defs
+auto_gen=
+NAME=cachedb_perf.so
+
+# The clusterer_controller pull transport is compiled only when that module is
+# part of this build - the top-level Makefile exports CLUSTERER_CTRL_SUPPORT=1
+# in that case (the clusterer module keys off the same hook).  Without it,
+# pulls and syncs use the clusterer module's bin links only, and an explicit
+# pull_transport=clctr warns and degrades to bin.
+ifeq ($(CLUSTERER_CTRL_SUPPORT),1)
+DEFS+= -DCLUSTERER_CTRL_SUPPORT
+endif
+
+include ../../Makefile.modules