BRIN de-summarization

When the BRIN summary tuple for a page range becomes too "wide" for the
values actually stored in the table (because the tuples that were
present originally are no longer present due to updates or deletes), it
can be useful to remove the outdated summary tuple, so that a future
summarization can install a tighter summary.

This commit introduces a SQL-callable interface to do so.

Author: Álvaro Herrera
Reviewed-by: Eiji Seki
Discussion: https://postgr.es/m/[email protected]

1 files changed, 43 insertions, 0 deletions

diff --git a/src/backend/access/brin/brin_xlog.c b/src/backend/access/brin/brin_xlog.c
index f416bacc3f7..8f5b5ceb3f2 100644
--- a/src/backend/access/brin/brin_xlog.c
+++ b/src/backend/access/brin/brin_xlog.c
@@ -254,6 +254,46 @@ brin_xlog_revmap_extend(XLogReaderState *record)
 		UnlockReleaseBuffer(metabuf);
 }
 
+static void
+brin_xlog_desummarize_page(XLogReaderState *record)
+{
+	XLogRecPtr	lsn = record->EndRecPtr;
+	xl_brin_desummarize *xlrec;
+	Buffer		buffer;
+	XLogRedoAction action;
+
+	xlrec = (xl_brin_desummarize *) XLogRecGetData(record);
+
+	/* Update the revmap */
+	action = XLogReadBufferForRedo(record, 0, &buffer);
+	if (action == BLK_NEEDS_REDO)
+	{
+		ItemPointerData	iptr;
+
+		ItemPointerSetInvalid(&iptr);
+		brinSetHeapBlockItemptr(buffer, xlrec->pagesPerRange, xlrec->heapBlk, iptr);
+
+		PageSetLSN(BufferGetPage(buffer), lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+
+	/* remove the leftover entry from the regular page */
+	action = XLogReadBufferForRedo(record, 1, &buffer);
+	if (action == BLK_NEEDS_REDO)
+	{
+		Page	regPg = BufferGetPage(buffer);
+
+		PageIndexTupleDeleteNoCompact(regPg, xlrec->regOffset);
+
+		PageSetLSN(regPg, lsn);
+		MarkBufferDirty(buffer);
+	}
+	if (BufferIsValid(buffer))
+		UnlockReleaseBuffer(buffer);
+}
+
 void
 brin_redo(XLogReaderState *record)
 {
@@ -276,6 +316,9 @@ brin_redo(XLogReaderState *record)
 		case XLOG_BRIN_REVMAP_EXTEND:
 			brin_xlog_revmap_extend(record);
 			break;
+		case XLOG_BRIN_DESUMMARIZE:
+			brin_xlog_desummarize_page(record);
+			break;
 		default:
 			elog(PANIC, "brin_redo: unknown op code %u", info);
 	}