1 files changed, 544 insertions, 0 deletions
diff --git a/src/backend/access/transam/generic_xlog.c b/src/backend/access/transam/generic_xlog.c
new file mode 100644
index 0000000..5164a1c
--- /dev/null
+++ b/src/backend/access/transam/generic_xlog.c
@@ -0,0 +1,544 @@
+/*-------------------------------------------------------------------------
+ *
+ * generic_xlog.c
+ *	 Implementation of generic xlog records.
+ *
+ *
+ * Portions Copyright (c) 1996-2020, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * src/backend/access/transam/generic_xlog.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "access/bufmask.h"
+#include "access/generic_xlog.h"
+#include "access/xlogutils.h"
+#include "miscadmin.h"
+#include "utils/memutils.h"
+
+/*-------------------------------------------------------------------------
+ * Internally, a delta between pages consists of a set of fragments.  Each
+ * fragment represents changes made in a given region of a page.  A fragment
+ * is made up as follows:
+ *
+ * - offset of page region (OffsetNumber)
+ * - length of page region (OffsetNumber)
+ * - data - the data to place into the region ('length' number of bytes)
+ *
+ * Unchanged regions of a page are not represented in its delta.  As a result,
+ * a delta can be more compact than the full page image.  But having an
+ * unchanged region between two fragments that is smaller than the fragment
+ * header (offset+length) does not pay off in terms of the overall size of
+ * the delta.  For this reason, we merge adjacent fragments if the unchanged
+ * region between them is <= MATCH_THRESHOLD bytes.
+ *
+ * We do not bother to merge fragments across the "lower" and "upper" parts
+ * of a page; it's very seldom the case that pd_lower and pd_upper are within
+ * MATCH_THRESHOLD bytes of each other, and handling that infrequent case
+ * would complicate and slow down the delta-computation code unduly.
+ * Therefore, the worst-case delta size includes two fragment headers plus
+ * a full page's worth of data.
+ *-------------------------------------------------------------------------
+ */
+#define FRAGMENT_HEADER_SIZE	(2 * sizeof(OffsetNumber))
+#define MATCH_THRESHOLD			FRAGMENT_HEADER_SIZE
+#define MAX_DELTA_SIZE			(BLCKSZ + 2 * FRAGMENT_HEADER_SIZE)
+
+/* Struct of generic xlog data for single page */
+typedef struct
+{
+	Buffer		buffer;			/* registered buffer */
+	int			flags;			/* flags for this buffer */
+	int			deltaLen;		/* space consumed in delta field */
+	char	   *image;			/* copy of page image for modification, do not
+								 * do it in-place to have aligned memory chunk */
+	char		delta[MAX_DELTA_SIZE];	/* delta between page images */
+} PageData;
+
+/* State of generic xlog record construction */
+struct GenericXLogState
+{
+	/* Info about each page, see above */
+	PageData	pages[MAX_GENERIC_XLOG_PAGES];
+	bool		isLogged;
+	/* Page images (properly aligned) */
+	PGAlignedBlock images[MAX_GENERIC_XLOG_PAGES];
+};
+
+static void writeFragment(PageData *pageData, OffsetNumber offset,
+						  OffsetNumber len, const char *data);
+static void computeRegionDelta(PageData *pageData,
+							   const char *curpage, const char *targetpage,
+							   int targetStart, int targetEnd,
+							   int validStart, int validEnd);
+static void computeDelta(PageData *pageData, Page curpage, Page targetpage);
+static void applyPageRedo(Page page, const char *delta, Size deltaSize);
+
+
+/*
+ * Write next fragment into pageData's delta.
+ *
+ * The fragment has the given offset and length, and data points to the
+ * actual data (of length length).
+ */
+static void
+writeFragment(PageData *pageData, OffsetNumber offset, OffsetNumber length,
+			  const char *data)
+{
+	char	   *ptr = pageData->delta + pageData->deltaLen;
+
+	/* Verify we have enough space */
+	Assert(pageData->deltaLen + sizeof(offset) +
+		   sizeof(length) + length <= sizeof(pageData->delta));
+
+	/* Write fragment data */
+	memcpy(ptr, &offset, sizeof(offset));
+	ptr += sizeof(offset);
+	memcpy(ptr, &length, sizeof(length));
+	ptr += sizeof(length);
+	memcpy(ptr, data, length);
+	ptr += length;
+
+	pageData->deltaLen = ptr - pageData->delta;
+}
+
+/*
+ * Compute the XLOG fragments needed to transform a region of curpage into the
+ * corresponding region of targetpage, and append them to pageData's delta
+ * field.  The region to transform runs from targetStart to targetEnd-1.
+ * Bytes in curpage outside the range validStart to validEnd-1 should be
+ * considered invalid, and always overwritten with target data.
+ *
+ * This function is a hot spot, so it's worth being as tense as possible
+ * about the data-matching loops.
+ */
+static void
+computeRegionDelta(PageData *pageData,
+				   const char *curpage, const char *targetpage,
+				   int targetStart, int targetEnd,
+				   int validStart, int validEnd)
+{
+	int			i,
+				loopEnd,
+				fragmentBegin = -1,
+				fragmentEnd = -1;
+
+	/* Deal with any invalid start region by including it in first fragment */
+	if (validStart > targetStart)
+	{
+		fragmentBegin = targetStart;
+		targetStart = validStart;
+	}
+
+	/* We'll deal with any invalid end region after the main loop */
+	loopEnd = Min(targetEnd, validEnd);
+
+	/* Examine all the potentially matchable bytes */
+	i = targetStart;
+	while (i < loopEnd)
+	{
+		if (curpage[i] != targetpage[i])
+		{
+			/* On unmatched byte, start new fragment if not already in one */
+			if (fragmentBegin < 0)
+				fragmentBegin = i;
+			/* Mark unmatched-data endpoint as uncertain */
+			fragmentEnd = -1;
+			/* Extend the fragment as far as possible in a tight loop */
+			i++;
+			while (i < loopEnd && curpage[i] != targetpage[i])
+				i++;
+			if (i >= loopEnd)
+				break;
+		}
+
+		/* Found a matched byte, so remember end of unmatched fragment */
+		fragmentEnd = i;
+
+		/*
+		 * Extend the match as far as possible in a tight loop.  (On typical
+		 * workloads, this inner loop is the bulk of this function's runtime.)
+		 */
+		i++;
+		while (i < loopEnd && curpage[i] == targetpage[i])
+			i++;
+
+		/*
+		 * There are several possible cases at this point:
+		 *
+		 * 1. We have no unwritten fragment (fragmentBegin < 0).  There's
+		 * nothing to write; and it doesn't matter what fragmentEnd is.
+		 *
+		 * 2. We found more than MATCH_THRESHOLD consecutive matching bytes.
+		 * Dump out the unwritten fragment, stopping at fragmentEnd.
+		 *
+		 * 3. The match extends to loopEnd.  We'll do nothing here, exit the
+		 * loop, and then dump the unwritten fragment, after merging it with
+		 * the invalid end region if any.  If we don't so merge, fragmentEnd
+		 * establishes how much the final writeFragment call needs to write.
+		 *
+		 * 4. We found an unmatched byte before loopEnd.  The loop will repeat
+		 * and will enter the unmatched-byte stanza above.  So in this case
+		 * also, it doesn't matter what fragmentEnd is.  The matched bytes
+		 * will get merged into the continuing unmatched fragment.
+		 *
+		 * Only in case 3 do we reach the bottom of the loop with a meaningful
+		 * fragmentEnd value, which is why it's OK that we unconditionally
+		 * assign "fragmentEnd = i" above.
+		 */
+		if (fragmentBegin >= 0 && i - fragmentEnd > MATCH_THRESHOLD)
+		{
+			writeFragment(pageData, fragmentBegin,
+						  fragmentEnd - fragmentBegin,
+						  targetpage + fragmentBegin);
+			fragmentBegin = -1;
+			fragmentEnd = -1;	/* not really necessary */
+		}
+	}
+
+	/* Deal with any invalid end region by including it in final fragment */
+	if (loopEnd < targetEnd)
+	{
+		if (fragmentBegin < 0)
+			fragmentBegin = loopEnd;
+		fragmentEnd = targetEnd;
+	}
+
+	/* Write final fragment if any */
+	if (fragmentBegin >= 0)
+	{
+		if (fragmentEnd < 0)
+			fragmentEnd = targetEnd;
+		writeFragment(pageData, fragmentBegin,
+					  fragmentEnd - fragmentBegin,
+					  targetpage + fragmentBegin);
+	}
+}
+
+/*
+ * Compute the XLOG delta record needed to transform curpage into targetpage,
+ * and store it in pageData's delta field.
+ */
+static void
+computeDelta(PageData *pageData, Page curpage, Page targetpage)
+{
+	int			targetLower = ((PageHeader) targetpage)->pd_lower,
+				targetUpper = ((PageHeader) targetpage)->pd_upper,
+				curLower = ((PageHeader) curpage)->pd_lower,
+				curUpper = ((PageHeader) curpage)->pd_upper;
+
+	pageData->deltaLen = 0;
+
+	/* Compute delta records for lower part of page ... */
+	computeRegionDelta(pageData, curpage, targetpage,
+					   0, targetLower,
+					   0, curLower);
+	/* ... and for upper part, ignoring what's between */
+	computeRegionDelta(pageData, curpage, targetpage,
+					   targetUpper, BLCKSZ,
+					   curUpper, BLCKSZ);
+
+	/*
+	 * If xlog debug is enabled, then check produced delta.  Result of delta
+	 * application to curpage should be equivalent to targetpage.
+	 */
+#ifdef WAL_DEBUG
+	if (XLOG_DEBUG)
+	{
+		PGAlignedBlock tmp;
+
+		memcpy(tmp.data, curpage, BLCKSZ);
+		applyPageRedo(tmp.data, pageData->delta, pageData->deltaLen);
+		if (memcmp(tmp.data, targetpage, targetLower) != 0 ||
+			memcmp(tmp.data + targetUpper, targetpage + targetUpper,
+				   BLCKSZ - targetUpper) != 0)
+			elog(ERROR, "result of generic xlog apply does not match");
+	}
+#endif
+}
+
+/*
+ * Start new generic xlog record for modifications to specified relation.
+ */
+GenericXLogState *
+GenericXLogStart(Relation relation)
+{
+	GenericXLogState *state;
+	int			i;
+
+	state = (GenericXLogState *) palloc(sizeof(GenericXLogState));
+	state->isLogged = RelationNeedsWAL(relation);
+
+	for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+	{
+		state->pages[i].image = state->images[i].data;
+		state->pages[i].buffer = InvalidBuffer;
+	}
+
+	return state;
+}
+
+/*
+ * Register new buffer for generic xlog record.
+ *
+ * Returns pointer to the page's image in the GenericXLogState, which
+ * is what the caller should modify.
+ *
+ * If the buffer is already registered, just return its existing entry.
+ * (It's not very clear what to do with the flags in such a case, but
+ * for now we stay with the original flags.)
+ */
+Page
+GenericXLogRegisterBuffer(GenericXLogState *state, Buffer buffer, int flags)
+{
+	int			block_id;
+
+	/* Search array for existing entry or first unused slot */
+	for (block_id = 0; block_id < MAX_GENERIC_XLOG_PAGES; block_id++)
+	{
+		PageData   *page = &state->pages[block_id];
+
+		if (BufferIsInvalid(page->buffer))
+		{
+			/* Empty slot, so use it (there cannot be a match later) */
+			page->buffer = buffer;
+			page->flags = flags;
+			memcpy(page->image, BufferGetPage(buffer), BLCKSZ);
+			return (Page) page->image;
+		}
+		else if (page->buffer == buffer)
+		{
+			/*
+			 * Buffer is already registered.  Just return the image, which is
+			 * already prepared.
+			 */
+			return (Page) page->image;
+		}
+	}
+
+	elog(ERROR, "maximum number %d of generic xlog buffers is exceeded",
+		 MAX_GENERIC_XLOG_PAGES);
+	/* keep compiler quiet */
+	return NULL;
+}
+
+/*
+ * Apply changes represented by GenericXLogState to the actual buffers,
+ * and emit a generic xlog record.
+ */
+XLogRecPtr
+GenericXLogFinish(GenericXLogState *state)
+{
+	XLogRecPtr	lsn;
+	int			i;
+
+	if (state->isLogged)
+	{
+		/* Logged relation: make xlog record in critical section. */
+		XLogBeginInsert();
+
+		START_CRIT_SECTION();
+
+		for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+		{
+			PageData   *pageData = &state->pages[i];
+			Page		page;
+			PageHeader	pageHeader;
+
+			if (BufferIsInvalid(pageData->buffer))
+				continue;
+
+			page = BufferGetPage(pageData->buffer);
+			pageHeader = (PageHeader) pageData->image;
+
+			if (pageData->flags & GENERIC_XLOG_FULL_IMAGE)
+			{
+				/*
+				 * A full-page image does not require us to supply any xlog
+				 * data.  Just apply the image, being careful to zero the
+				 * "hole" between pd_lower and pd_upper in order to avoid
+				 * divergence between actual page state and what replay would
+				 * produce.
+				 */
+				memcpy(page, pageData->image, pageHeader->pd_lower);
+				memset(page + pageHeader->pd_lower, 0,
+					   pageHeader->pd_upper - pageHeader->pd_lower);
+				memcpy(page + pageHeader->pd_upper,
+					   pageData->image + pageHeader->pd_upper,
+					   BLCKSZ - pageHeader->pd_upper);
+
+				XLogRegisterBuffer(i, pageData->buffer,
+								   REGBUF_FORCE_IMAGE | REGBUF_STANDARD);
+			}
+			else
+			{
+				/*
+				 * In normal mode, calculate delta and write it as xlog data
+				 * associated with this page.
+				 */
+				computeDelta(pageData, page, (Page) pageData->image);
+
+				/* Apply the image, with zeroed "hole" as above */
+				memcpy(page, pageData->image, pageHeader->pd_lower);
+				memset(page + pageHeader->pd_lower, 0,
+					   pageHeader->pd_upper - pageHeader->pd_lower);
+				memcpy(page + pageHeader->pd_upper,
+					   pageData->image + pageHeader->pd_upper,
+					   BLCKSZ - pageHeader->pd_upper);
+
+				XLogRegisterBuffer(i, pageData->buffer, REGBUF_STANDARD);
+				XLogRegisterBufData(i, pageData->delta, pageData->deltaLen);
+			}
+		}
+
+		/* Insert xlog record */
+		lsn = XLogInsert(RM_GENERIC_ID, 0);
+
+		/* Set LSN and mark buffers dirty */
+		for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+		{
+			PageData   *pageData = &state->pages[i];
+
+			if (BufferIsInvalid(pageData->buffer))
+				continue;
+			PageSetLSN(BufferGetPage(pageData->buffer), lsn);
+			MarkBufferDirty(pageData->buffer);
+		}
+		END_CRIT_SECTION();
+	}
+	else
+	{
+		/* Unlogged relation: skip xlog-related stuff */
+		START_CRIT_SECTION();
+		for (i = 0; i < MAX_GENERIC_XLOG_PAGES; i++)
+		{
+			PageData   *pageData = &state->pages[i];
+
+			if (BufferIsInvalid(pageData->buffer))
+				continue;
+			memcpy(BufferGetPage(pageData->buffer),
+				   pageData->image,
+				   BLCKSZ);
+			/* We don't worry about zeroing the "hole" in this case */
+			MarkBufferDirty(pageData->buffer);
+		}
+		END_CRIT_SECTION();
+		/* We don't have a LSN to return, in this case */
+		lsn = InvalidXLogRecPtr;
+	}
+
+	pfree(state);
+
+	return lsn;
+}
+
+/*
+ * Abort generic xlog record construction.  No changes are applied to buffers.
+ *
+ * Note: caller is responsible for releasing locks/pins on buffers, if needed.
+ */
+void
+GenericXLogAbort(GenericXLogState *state)
+{
+	pfree(state);
+}
+
+/*
+ * Apply delta to given page image.
+ */
+static void
+applyPageRedo(Page page, const char *delta, Size deltaSize)
+{
+	const char *ptr = delta;
+	const char *end = delta + deltaSize;
+
+	while (ptr < end)
+	{
+		OffsetNumber offset,
+					length;
+
+		memcpy(&offset, ptr, sizeof(offset));
+		ptr += sizeof(offset);
+		memcpy(&length, ptr, sizeof(length));
+		ptr += sizeof(length);
+
+		memcpy(page + offset, ptr, length);
+
+		ptr += length;
+	}
+}
+
+/*
+ * Redo function for generic xlog record.
+ */
+void
+generic_redo(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	Buffer		buffers[MAX_GENERIC_XLOG_PAGES];
+	uint8		block_id;
+
+	/* Protect limited size of buffers[] array */
+	Assert(record->max_block_id < MAX_GENERIC_XLOG_PAGES);
+
+	/* Iterate over blocks */
+	for (block_id = 0; block_id <= record->max_block_id; block_id++)
+	{
+		XLogRedoAction action;
+
+		if (!XLogRecHasBlockRef(record, block_id))
+		{
+			buffers[block_id] = InvalidBuffer;
+			continue;
+		}
+
+		action = XLogReadBufferForRedo(record, block_id, &buffers[block_id]);
+
+		/* Apply redo to given block if needed */
+		if (action == BLK_NEEDS_REDO)
+		{
+			Page		page;
+			PageHeader	pageHeader;
+			char	   *blockDelta;
+			Size		blockDeltaSize;
+
+			page = BufferGetPage(buffers[block_id]);
+			blockDelta = XLogRecGetBlockData(record, block_id, &blockDeltaSize);
+			applyPageRedo(page, blockDelta, blockDeltaSize);
+
+			/*
+			 * Since the delta contains no information about what's in the
+			 * "hole" between pd_lower and pd_upper, set that to zero to
+			 * ensure we produce the same page state that application of the
+			 * logged action by GenericXLogFinish did.
+			 */
+			pageHeader = (PageHeader) page;
+			memset(page + pageHeader->pd_lower, 0,
+				   pageHeader->pd_upper - pageHeader->pd_lower);
+
+			PageSetLSN(page, lsn);
+			MarkBufferDirty(buffers[block_id]);
+		}
+	}
+
+	/* Changes are done: unlock and release all buffers */
+	for (block_id = 0; block_id <= record->max_block_id; block_id++)
+	{
+		if (BufferIsValid(buffers[block_id]))
+			UnlockReleaseBuffer(buffers[block_id]);
+	}
+}
+
+/*
+ * Mask a generic page before performing consistency checks on it.
+ */
+void
+generic_mask(char *page, BlockNumber blkno)
+{
+	mask_page_lsn_and_checksum(page);
+
+	mask_unused_space(page);
+}