LSM

Makefile

+MODULE_big = lsm
+OBJS = lsm.o
+PGFILEDESC = "lsm tree index based on existing btree index"
+#MODULES = lsm.o
+EXTENSION = lsm
+DATA = lsm--1.0.sql
+
+REGRESS = test
+REGRESS_OPTS = --temp-config $(top_srcdir)/contrib/lsm3/lsm3.conf
+
+
+ifdef USE_PGXS
+PG_CONFIG ?= pg_config
+PGXS := $(shell $(PG_CONFIG) --pgxs)
+include $(PGXS)
+else
+subdir = contrib/lsm3
+top_builddir = ../..
+include $(top_builddir)/src/Makefile.global
+include $(top_srcdir)/contrib/contrib-global.mk
+endif

lsm.control

+comment = 'Lsm index'
+default_version = '1.0'
+module_pathname = '$libdir/lsm'
+relocatable = true

lsm.h

+/*
+ * It is too expensive to check index size at each insert because it requires traverse of all index file segments and calling lseek for each.
+ * But we do not need precise size, so it is enough to do it at each n-th insert. The lagest B-Tree key size is abut 2kb,
+ * so with N=64K in the worst case error will be less than 128Mb and for 32-bit key just 1Mb.
+ */
+#define LSM3_CHECK_TOP_INDEX_SIZE_PERIOD (64*1024) /* should be power of two */
+
+/*
+ * Control structure for Lsm3 index located in shared memory
+ */
+typedef struct
+{
+	Oid base;   /* Oid of base index */
+	Oid heap;   /* Oid of indexed relation */
+	Oid top[2]; /* Oids of two top indexes */
+	int access_count[2]; /* Access counter for top indexes */
+	int active_index; /* Index used for insert */
+	uint64 n_merges;  /* Number of performed merges since database open */
+	uint64 n_inserts; /* Number of performed inserts since database open  */
+	volatile bool start_merge; /* Start merging of top index with base index */
+	volatile bool merge_in_progress; /* Overflow of top index intiate merge process */
+	PGPROC* merger;   /* Merger background worker */
+	Oid     db_id;    /* user ID (for background worker) */
+	Oid     user_id;  /* database Id (for background worker) */
+	int     top_index_size; /* Size of top index */
+	slock_t spinlock; /* Spinlock to synchronize access */
+} Lsm3DictEntry;
+
+/*
+ * Opaque part of index scan descriptor
+ */
+typedef struct
+{
+	Lsm3DictEntry* entry;      /* Lsm3 control structure */
+	Relation 	   top_index[2]; /* Opened top index relations */
+	SortSupport    sortKeys;   /* Context for comparing index tuples */
+	IndexScanDesc  scan[3];    /* Scan descriptors for two top indexes and base index */
+	bool           eof[3];     /* Indicators that end of index was reached */
+	bool           unique;     /* Whether index is "unique" and we can stop scan after locating first occurrence */
+	int            curr_index; /* Index from which last tuple was selected (or -1 if none) */
+} Lsm3ScanOpaque;
+
+/* Lsm3 index options */
+typedef struct
+{
+	BTOptions   nbt_opts;       /* Standard B-Tree options */
+	int         top_index_size; /* Size of top index (overrode lsm3.top_index_size GUC */
+	bool        unique;			/* Index may not contain duplicates. We prohibit unique constraint for Lsm3 index
+                                 * because it can not be enforced. But presence of this index option allows to optimize
+								 * index lookup: if key is found in active top index, do not search other two indexes.
+                                 */
+} Lsm3Options;