Add TIDStore, to store sets of TIDs (ItemPointerData) efficiently.

TIDStore is a data structure designed to efficiently store large sets
of TIDs. For TID storage, it employs a radix tree, where the key is
a block number, and the value is a bitmap representing offset
numbers. The TIDStore can be created on a DSA area and used by
multiple backend processes simultaneously.

There are potential future users such as tidbitmap.c, though it's very
likely the interface will need to evolve as we come to understand the
needs of different kinds of users. For example, we can support
updating the offset bitmap of existing values.

Currently, the TIDStore is not used for anything yet, aside from the
test code. But an upcoming patch will use it.

This includes a unit test module, in src/test/modules/test_tidstore.

Co-authored-by: John Naylor
Discussion: https://postgr.es/m/CAD21AoAfOZvmfR0j8VmZorZjL7RhTiQdVttNuC4W-Shdc2a-AA%40mail.gmail.com

3 files changed, 465 insertions, 0 deletions

diff --git a/src/backend/access/common/Makefile b/src/backend/access/common/Makefile
index b9aff0ccfdc..e78de312659 100644
--- a/src/backend/access/common/Makefile
+++ b/src/backend/access/common/Makefile
@@ -25,6 +25,7 @@ OBJS = \
 	scankey.o \
 	session.o \
 	syncscan.o \
+	tidstore.o \
 	toast_compression.o \
 	toast_internals.o \
 	tupconvert.o \
diff --git a/src/backend/access/common/meson.build b/src/backend/access/common/meson.build
index 725041a4ce2..14090c728fb 100644
--- a/src/backend/access/common/meson.build
+++ b/src/backend/access/common/meson.build
@@ -13,6 +13,7 @@ backend_sources += files(
   'scankey.c',
   'session.c',
   'syncscan.c',
+  'tidstore.c',
   'toast_compression.c',
   'toast_internals.c',
   'tupconvert.c',
diff --git a/src/backend/access/common/tidstore.c b/src/backend/access/common/tidstore.c
new file mode 100644
index 00000000000..745393806d3
--- /dev/null
+++ b/src/backend/access/common/tidstore.c
@@ -0,0 +1,463 @@
+/*-------------------------------------------------------------------------
+ *
+ * tidstore.c
+ *		TID (ItemPointerData) storage implementation.
+ *
+ * TidStore is a in-memory data structure to store TIDs (ItemPointerData).
+ * Internally it uses a radix tree as the storage for TIDs. The key is the
+ * BlockNumber and the value is a bitmap of offsets, BlocktableEntry.
+ *
+ * TidStore can be shared among parallel worker processes by passing DSA area
+ * to TidStoreCreate(). Other backends can attach to the shared TidStore by
+ * TidStoreAttach().
+ *
+ * Portions Copyright (c) 1996-2024, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * IDENTIFICATION
+ *	  src/backend/access/common/tidstore.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/tidstore.h"
+#include "miscadmin.h"
+#include "nodes/bitmapset.h"
+#include "storage/lwlock.h"
+#include "utils/dsa.h"
+
+
+#define WORDNUM(x)	((x) / BITS_PER_BITMAPWORD)
+#define BITNUM(x)	((x) % BITS_PER_BITMAPWORD)
+
+/* number of active words for a page: */
+#define WORDS_PER_PAGE(n) ((n) / BITS_PER_BITMAPWORD + 1)
+
+/*
+ * This is named similarly to PagetableEntry in tidbitmap.c
+ * because the two have a similar function.
+ */
+typedef struct BlocktableEntry
+{
+	uint16		nwords;
+	bitmapword	words[FLEXIBLE_ARRAY_MEMBER];
+} BlocktableEntry;
+#define MaxBlocktableEntrySize \
+	offsetof(BlocktableEntry, words) + \
+		(sizeof(bitmapword) * WORDS_PER_PAGE(MaxOffsetNumber))
+
+#define RT_PREFIX local_ts
+#define RT_SCOPE static
+#define RT_DECLARE
+#define RT_DEFINE
+#define RT_VALUE_TYPE BlocktableEntry
+#define RT_VARLEN_VALUE_SIZE(page) \
+	(offsetof(BlocktableEntry, words) + \
+	sizeof(bitmapword) * (page)->nwords)
+#include "lib/radixtree.h"
+
+#define RT_PREFIX shared_ts
+#define RT_SHMEM
+#define RT_SCOPE static
+#define RT_DECLARE
+#define RT_DEFINE
+#define RT_VALUE_TYPE BlocktableEntry
+#define RT_VARLEN_VALUE_SIZE(page) \
+	(offsetof(BlocktableEntry, words) + \
+	sizeof(bitmapword) * (page)->nwords)
+#include "lib/radixtree.h"
+
+/* Per-backend state for a TidStore */
+struct TidStore
+{
+	/* MemoryContext where the TidStore is allocated */
+	MemoryContext context;
+
+	/* MemoryContext that the radix tree uses */
+	MemoryContext rt_context;
+
+	/* Storage for TIDs. Use either one depending on TidStoreIsShared() */
+	union
+	{
+		local_ts_radix_tree *local;
+		shared_ts_radix_tree *shared;
+	}			tree;
+
+	/* DSA area for TidStore if using shared memory */
+	dsa_area   *area;
+};
+#define TidStoreIsShared(ts) ((ts)->area != NULL)
+
+/* Iterator for TidStore */
+struct TidStoreIter
+{
+	TidStore   *ts;
+
+	/* iterator of radix tree. Use either one depending on TidStoreIsShared() */
+	union
+	{
+		shared_ts_iter *shared;
+		local_ts_iter *local;
+	}			tree_iter;
+
+	/* output for the caller */
+	TidStoreIterResult output;
+};
+
+static void tidstore_iter_extract_tids(TidStoreIter *iter, BlockNumber blkno,
+									   BlocktableEntry *page);
+
+/*
+ * Create a TidStore. The TidStore will live in the memory context that is
+ * CurrentMemoryContext at the time of this call. The TID storage, backed
+ * by a radix tree, will live in its child memory context, rt_context. The
+ * TidStore will be limited to (approximately) max_bytes total memory
+ * consumption. If the 'area' is non-NULL, the radix tree is created in the
+ * DSA area.
+ *
+ * The returned object is allocated in backend-local memory.
+ */
+TidStore *
+TidStoreCreate(size_t max_bytes, dsa_area *area, int tranche_id)
+{
+	TidStore   *ts;
+	size_t		initBlockSize = ALLOCSET_DEFAULT_INITSIZE;
+	size_t		minContextSize = ALLOCSET_DEFAULT_MINSIZE;
+	size_t		maxBlockSize = ALLOCSET_DEFAULT_MAXSIZE;
+
+	ts = palloc0(sizeof(TidStore));
+	ts->context = CurrentMemoryContext;
+
+	/* choose the maxBlockSize to be no larger than 1/16 of max_bytes */
+	while (16 * maxBlockSize > max_bytes * 1024L)
+		maxBlockSize >>= 1;
+
+	if (maxBlockSize < ALLOCSET_DEFAULT_INITSIZE)
+		maxBlockSize = ALLOCSET_DEFAULT_INITSIZE;
+
+	/* Create a memory context for the TID storage */
+	ts->rt_context = AllocSetContextCreate(CurrentMemoryContext,
+										   "TID storage",
+										   minContextSize,
+										   initBlockSize,
+										   maxBlockSize);
+
+	if (area != NULL)
+	{
+		ts->tree.shared = shared_ts_create(ts->rt_context, area,
+										   tranche_id);
+		ts->area = area;
+	}
+	else
+		ts->tree.local = local_ts_create(ts->rt_context);
+
+	return ts;
+}
+
+/*
+ * Attach to the shared TidStore using the given  handle. The returned object
+ * is allocated in backend-local memory using the CurrentMemoryContext.
+ */
+TidStore *
+TidStoreAttach(dsa_area *area, dsa_pointer handle)
+{
+	TidStore   *ts;
+
+	Assert(area != NULL);
+	Assert(DsaPointerIsValid(handle));
+
+	/* create per-backend state */
+	ts = palloc0(sizeof(TidStore));
+
+	/* Find the shared the shared radix tree */
+	ts->tree.shared = shared_ts_attach(area, handle);
+	ts->area = area;
+
+	return ts;
+}
+
+/*
+ * Detach from a TidStore. This detaches from radix tree and frees the
+ * backend-local resources. The radix tree will continue to exist until
+ * it is either explicitly destroyed, or the area that backs it is returned
+ * to the operating system.
+ */
+void
+TidStoreDetach(TidStore *ts)
+{
+	Assert(TidStoreIsShared(ts));
+
+	shared_ts_detach(ts->tree.shared);
+	pfree(ts);
+}
+
+/*
+ * Lock support functions.
+ *
+ * We can use the radix tree's lock for shared TidStore as the data we
+ * need to protect is only the shared radix tree.
+ */
+
+void
+TidStoreLockExclusive(TidStore *ts)
+{
+	if (TidStoreIsShared(ts))
+		shared_ts_lock_exclusive(ts->tree.shared);
+}
+
+void
+TidStoreLockShare(TidStore *ts)
+{
+	if (TidStoreIsShared(ts))
+		shared_ts_lock_share(ts->tree.shared);
+}
+
+void
+TidStoreUnlock(TidStore *ts)
+{
+	if (TidStoreIsShared(ts))
+		shared_ts_unlock(ts->tree.shared);
+}
+
+/*
+ * Destroy a TidStore, returning all memory.
+ *
+ * Note that the caller must be certain that no other backend will attempt to
+ * access the TidStore before calling this function. Other backend must
+ * explicitly call TidStoreDetach() to free up backend-local memory associated
+ * with the TidStore. The backend that calls TidStoreDestroy() must not call
+ * TidStoreDetach().
+ */
+void
+TidStoreDestroy(TidStore *ts)
+{
+	/* Destroy underlying radix tree */
+	if (TidStoreIsShared(ts))
+		shared_ts_free(ts->tree.shared);
+	else
+		local_ts_free(ts->tree.local);
+
+	MemoryContextDelete(ts->rt_context);
+
+	pfree(ts);
+}
+
+/*
+ * Create or replace an entry for the given block and array of offsets.
+ *
+ * NB: This function is designed and optimized for vacuum's heap scanning
+ * phase, so has some limitations:
+ *
+ * - The offset numbers "offsets" must be sorted in ascending order.
+ * - If the block number already exists, the entry will be replaced --
+ *	 there is no way to add or remove offsets from an entry.
+ */
+void
+TidStoreSetBlockOffsets(TidStore *ts, BlockNumber blkno, OffsetNumber *offsets,
+						int num_offsets)
+{
+	char		data[MaxBlocktableEntrySize];
+	BlocktableEntry *page = (BlocktableEntry *) data;
+	bitmapword	word;
+	int			wordnum;
+	int			next_word_threshold;
+	int			idx = 0;
+
+	Assert(num_offsets > 0);
+
+	/* Check if the given offset numbers are ordered */
+	for (int i = 1; i < num_offsets; i++)
+		Assert(offsets[i] > offsets[i - 1]);
+
+	for (wordnum = 0, next_word_threshold = BITS_PER_BITMAPWORD;
+		 wordnum <= WORDNUM(offsets[num_offsets - 1]);
+		 wordnum++, next_word_threshold += BITS_PER_BITMAPWORD)
+	{
+		word = 0;
+
+		while (idx < num_offsets)
+		{
+			OffsetNumber off = offsets[idx];
+
+			/* safety check to ensure we don't overrun bit array bounds */
+			if (!OffsetNumberIsValid(off))
+				elog(ERROR, "tuple offset out of range: %u", off);
+
+			if (off >= next_word_threshold)
+				break;
+
+			word |= ((bitmapword) 1 << BITNUM(off));
+			idx++;
+		}
+
+		/* write out offset bitmap for this wordnum */
+		page->words[wordnum] = word;
+	}
+
+	page->nwords = wordnum;
+	Assert(page->nwords == WORDS_PER_PAGE(offsets[num_offsets - 1]));
+
+	if (TidStoreIsShared(ts))
+		shared_ts_set(ts->tree.shared, blkno, page);
+	else
+		local_ts_set(ts->tree.local, blkno, page);
+}
+
+/* Return true if the given TID is present in the TidStore */
+bool
+TidStoreIsMember(TidStore *ts, ItemPointer tid)
+{
+	int			wordnum;
+	int			bitnum;
+	BlocktableEntry *page;
+	BlockNumber blk = ItemPointerGetBlockNumber(tid);
+	OffsetNumber off = ItemPointerGetOffsetNumber(tid);
+
+	if (TidStoreIsShared(ts))
+		page = shared_ts_find(ts->tree.shared, blk);
+	else
+		page = local_ts_find(ts->tree.local, blk);
+
+	/* no entry for the blk */
+	if (page == NULL)
+		return false;
+
+	wordnum = WORDNUM(off);
+	bitnum = BITNUM(off);
+
+	/* no bitmap for the off */
+	if (wordnum >= page->nwords)
+		return false;
+
+	return (page->words[wordnum] & ((bitmapword) 1 << bitnum)) != 0;
+}
+
+/*
+ * Prepare to iterate through a TidStore.
+ *
+ * The TidStoreIter struct is created in the caller's memory context, and it
+ * will be freed in TidStoreEndIterate.
+ *
+ * The caller is responsible for locking TidStore until the iteration is
+ * finished.
+ */
+TidStoreIter *
+TidStoreBeginIterate(TidStore *ts)
+{
+	TidStoreIter *iter;
+
+	iter = palloc0(sizeof(TidStoreIter));
+	iter->ts = ts;
+
+	/*
+	 * We start with an array large enough to contain at least the offsets
+	 * from one completely full bitmap element.
+	 */
+	iter->output.max_offset = 2 * BITS_PER_BITMAPWORD;
+	iter->output.offsets = palloc(sizeof(OffsetNumber) * iter->output.max_offset);
+
+	if (TidStoreIsShared(ts))
+		iter->tree_iter.shared = shared_ts_begin_iterate(ts->tree.shared);
+	else
+		iter->tree_iter.local = local_ts_begin_iterate(ts->tree.local);
+
+	return iter;
+}
+
+
+/*
+ * Scan the TidStore and return the TIDs of the next block. The offsets in
+ * each iteration result are ordered, as are the block numbers over all
+ * iterations.
+ */
+TidStoreIterResult *
+TidStoreIterateNext(TidStoreIter *iter)
+{
+	uint64		key;
+	BlocktableEntry *page;
+
+	if (TidStoreIsShared(iter->ts))
+		page = shared_ts_iterate_next(iter->tree_iter.shared, &key);
+	else
+		page = local_ts_iterate_next(iter->tree_iter.local, &key);
+
+	if (page == NULL)
+		return NULL;
+
+	/* Collect TIDs from the key-value pair */
+	tidstore_iter_extract_tids(iter, (BlockNumber) key, page);
+
+	return &(iter->output);
+}
+
+/*
+ * Finish the iteration on TidStore.
+ *
+ * The caller is responsible for releasing any locks.
+ */
+void
+TidStoreEndIterate(TidStoreIter *iter)
+{
+	if (TidStoreIsShared(iter->ts))
+		shared_ts_end_iterate(iter->tree_iter.shared);
+	else
+		local_ts_end_iterate(iter->tree_iter.local);
+
+	pfree(iter->output.offsets);
+	pfree(iter);
+}
+
+/*
+ * Return the memory usage of TidStore.
+ */
+size_t
+TidStoreMemoryUsage(TidStore *ts)
+{
+	if (TidStoreIsShared(ts))
+		return shared_ts_memory_usage(ts->tree.shared);
+	else
+		return local_ts_memory_usage(ts->tree.local);
+}
+
+dsa_pointer
+TidStoreGetHandle(TidStore *ts)
+{
+	Assert(TidStoreIsShared(ts));
+
+	return (dsa_pointer) shared_ts_get_handle(ts->tree.shared);
+}
+
+/* Extract TIDs from the given key-value pair */
+static void
+tidstore_iter_extract_tids(TidStoreIter *iter, BlockNumber blkno,
+						   BlocktableEntry *page)
+{
+	TidStoreIterResult *result = (&iter->output);
+	int			wordnum;
+
+	result->num_offsets = 0;
+	result->blkno = blkno;
+
+	for (wordnum = 0; wordnum < page->nwords; wordnum++)
+	{
+		bitmapword	w = page->words[wordnum];
+		int			off = wordnum * BITS_PER_BITMAPWORD;
+
+		/* Make sure there is enough space to add offsets */
+		if ((result->num_offsets + BITS_PER_BITMAPWORD) > result->max_offset)
+		{
+			result->max_offset *= 2;
+			result->offsets = repalloc(result->offsets,
+									   sizeof(OffsetNumber) * result->max_offset);
+		}
+
+		while (w != 0)
+		{
+			if (w & 1)
+				result->offsets[result->num_offsets++] = (OffsetNumber) off;
+			off++;
+			w >>= 1;
+		}
+	}
+}