Hello,
> Parallel version is not supported, but I think it should be possible.
@Tomas are you working on this ? If not, I would like to give it a try.
> static void
> AssertCheckRanges(BrinSortState *node)
> {
> #ifdef USE_ASSERT_CHECKING
>
> #endif
> }
I guess it should not be empty at the ongoing development stage.
Attached a small modification of the patch with a draft of the docs.
Regards,
Sergey Dudoladov
From d4050be4bfd0a518eba0ff0a7b561f0420be9861 Mon Sep 17 00:00:00 2001
From: Sergey Dudoladov <[email protected]>
Date: Wed, 2 Aug 2023 16:47:35 +0200
Subject: [PATCH] BRIN sort: add docs / fix typos
---
doc/src/sgml/brin.sgml | 48 +++++++++++++++++++++++++++++
src/backend/executor/nodeBrinSort.c | 9 +++---
2 files changed, 53 insertions(+), 4 deletions(-)
diff --git a/doc/src/sgml/brin.sgml b/doc/src/sgml/brin.sgml
index 9c5ffcddf8..a76f26e032 100644
--- a/doc/src/sgml/brin.sgml
+++ b/doc/src/sgml/brin.sgml
@@ -810,6 +810,54 @@ LOG: request for BRIN range summarization for index "brin_wi_idx" page 128 was
</sect1>
+<sect1 id="brin-sort">
+ <title>BRIN Sort</title>
+
+ <para>
+ This section provides an overview of <acronym>BRIN</acronym> sort that may be
+ useful to advanced users. See <filename>src/backend/executor/nodeBrinSort.c</filename>
+ in the source distribution for the implementation.
+ </para>
+
+ <sect2 id="brin-sort-overview">
+ <title>Overview</title>
+ <para>
+ The information about ranges in a <acronym>BRIN</acronym> index can be used
+ to split a table into parts and sort each part separately. A <acronym>BRIN</acronym>
+ sort is an index scan that uses the idea to incrementally sort the data. On
+ large tables <acronym>BRIN</acronym> index scan bridges the performance gap
+ between having a large B-tree index that supports ordered retrieval, and having
+ no index at all.
+ </para>
+ </sect2>
+
+ <sect2 id="brin-sort-implementation">
+ <title>Implementation</title>
+ <para>
+
+ <acronym>BRIN</acronym> sort fetches a list of page ranges from the <acronym>BRIN</acronym>
+ index and sorts them by their summary info depending on the operator class and
+ sort direction. It then determines the watermark: the next summary value from
+ the list. Tuples with summary values less than the watermark are sorted and
+ outputted directly; tuples with values greater than the watermark are spilled
+ into the next iteration. The process continues until either all ranges are
+ processed or the desired number of tuples has been retrieved.
+ </para>
+ </sect2>
+
+ <sect2 id="brin-sort-limitations">
+ <title>Limitations</title>
+ <para>
+ The performance of the <acronym>BRIN</acronym> sort depends on the degree of
+ correlation between the values of the indexed column and their physical location
+ on disk: in the case of high correlation, there will be few overlapping ranges,
+ and performance will be best. Another limitation is that <acronym>BRIN</acronym>
+ sort only works for indexes built on a single column.
+ </para>
+ </sect2>
+
+</sect1>
+
<sect1 id="brin-extensibility">
<title>Extensibility</title>
diff --git a/src/backend/executor/nodeBrinSort.c b/src/backend/executor/nodeBrinSort.c
index d1b6b4e1ed..c640aea2d5 100644
--- a/src/backend/executor/nodeBrinSort.c
+++ b/src/backend/executor/nodeBrinSort.c
@@ -731,8 +731,9 @@ brinsort_load_spill_tuples(BrinSortState *node, bool check_watermark)
static bool
brinsort_next_range(BrinSortState *node, bool asc)
{
- /* FIXME free the current bs_range, if any */
- node->bs_range = NULL;
+ /* free the current bs_range, if any */
+ if (node->bs_range != NULL)
+ pfree(node->bs_range);
/*
* Mark the position, so that we can restore it in case we reach the
@@ -1227,7 +1228,7 @@ IndexNext(BrinSortState *node)
case BRINSORT_PROCESS_RANGE:
- elog(DEBUG1, "phase BRINSORT_PROCESS_RANGE");
+ elog(DEBUG1, "phase = BRINSORT_PROCESS_RANGE");
slot = node->ss.ps.ps_ResultTupleSlot;
@@ -1263,7 +1264,7 @@ IndexNext(BrinSortState *node)
}
else
{
- /* updte the watermark and try reading more ranges */
+ /* update the watermark and try reading more ranges */
node->bs_phase = BRINSORT_LOAD_RANGE;
brinsort_update_watermark(node, false, asc);
}
--
2.34.1
