From e187693239ad99fcfa368811f51fcf8af7428082 Mon Sep 17 00:00:00 2001 From: Tomas Vondra Date: Fri, 19 May 2023 00:00:22 +0200 Subject: [PATCH] Fix handling of empty ranges and NULLs in BRIN BRIN indexes did not properly distinguish between summaries for empty (no rows) and all-NULL ranges, treating them as essentially the same thing. Summaries were initialized with allnulls=true, and opclasses simply reset allnulls to false when processing the first non-NULL value. This however produces incorrect results if the range starts with a NULL value (or a sequence of NULL values), in which case we forget the range contains NULL values when adding the first non-NULL value. This happens because the allnulls flag is used for two separate purposes - to mark empty ranges (not representing any rows yet) and ranges containing only NULL values. Opclasses don't know which of these cases it is, and so don't know whether to set hasnulls=true. Setting the flag in both cases would make it correct, but it would also make BRIN indexes useless for queries with IS NULL clauses. All ranges start empty (and thus allnulls=true), so all ranges would end up with either allnulls=true or hasnulls=true. The severity of the issue is somewhat reduced by the fact that it only happens when adding values to an existing summary with allnulls=true. This can happen e.g. for small tables (because a summary for the first range exists for all BRIN indexes), or for tables with large fraction of NULL values in the indexed columns. Bulk summarization (e.g. during CREATE INDEX or automatic summarization) that processes all values at once is not affected by this issue. In this case the flags were updated in a slightly different way, not forgetting the NULL values. To identify empty ranges we use a new flag, stored in an unused bit in the BRIN tuple header so the on-disk format remains the same. A matching flag is added to BrinMemTuple, into a 3B gap after bt_placeholder. That means there's no risk of ABI breakage, although we don't actually pass the BrinMemTuple to any public API. We could also skip storing index tuples for empty summaries, but then we'd have to always process such ranges - even if there are no rows in large parts of the table (e.g. after a bulk DELETE), it would still require reading the pages etc. So we store them, but ignore them when building the bitmap. Backpatch to 11. The issue exists since BRIN indexes were introduced in 9.5, but older releases are already EOL. Backpatch-through: 11 Reviewed-by: Justin Pryzby, Matthias van de Meent, Alvaro Herrera Discussion: https://postgr.es/m/402430e4-7d9d-6cf1-09ef-464d80afff3b@enterprisedb.com --- src/backend/access/brin/brin.c | 113 +++++++++++++++++- src/backend/access/brin/brin_tuple.c | 14 ++- src/include/access/brin_tuple.h | 6 +- ...summarization-and-inprogress-insertion.out | 8 +- ...ummarization-and-inprogress-insertion.spec | 1 + 5 files changed, 134 insertions(+), 8 deletions(-) diff --git a/src/backend/access/brin/brin.c b/src/backend/access/brin/brin.c index fdf74256fc..5d17d7013a 100644 --- a/src/backend/access/brin/brin.c +++ b/src/backend/access/brin/brin.c @@ -591,6 +591,17 @@ bringetbitmap(IndexScanDesc scan, TIDBitmap *tbm) bval = &dtup->bt_columns[attno - 1]; + /* + * If the BRIN tuple indicates that this range is empty, + * we can skip it: there's nothing to match. We don't + * need to examine the next columns. + */ + if (dtup->bt_empty_range) + { + addrange = false; + break; + } + /* * First check if there are any IS [NOT] NULL scan keys, * and if we're violating them. In that case we can @@ -1606,6 +1617,64 @@ union_tuples(BrinDesc *bdesc, BrinMemTuple *a, BrinTuple *b) db = brin_deform_tuple(bdesc, b, NULL); MemoryContextSwitchTo(oldcxt); + /* + * Check if the ranges are empty. + * + * If at least one of them is empty, we don't need to call per-key union + * functions at all. If "b" is empty, we just use "a" as the result (it + * might be empty fine, but that's fine). If "a" is empty but "b" is not, + * we use "b" as the result (but we have to copy the data into "a" first). + * + * Only when both ranges are non-empty, we actually do the per-key merge. + */ + + /* If "b" is empty - ignore it and just use "a" (even if it's empty etc.). */ + if (db->bt_empty_range) + { + /* skip the per-key merge */ + MemoryContextDelete(cxt); + return; + } + + /* + * Now we know "b" is not empty. If "a" is empty, then "b" is the result. + * But we need to copy the data from "b" to "a" first, because that's how + * we pass result out. + * + * We have to copy all the global/per-key flags etc. too. + */ + if (a->bt_empty_range) + { + for (keyno = 0; keyno < bdesc->bd_tupdesc->natts; keyno++) + { + int i; + BrinValues *col_a = &a->bt_columns[keyno]; + BrinValues *col_b = &db->bt_columns[keyno]; + BrinOpcInfo *opcinfo = bdesc->bd_info[keyno]; + + col_a->bv_allnulls = col_b->bv_allnulls; + col_a->bv_hasnulls = col_b->bv_hasnulls; + + /* If "b" has no data, we're done. */ + if (col_b->bv_allnulls) + continue; + + for (i = 0; i < opcinfo->oi_nstored; i++) + col_a->bv_values[i] = + datumCopy(col_b->bv_values[i], + opcinfo->oi_typcache[i]->typbyval, + opcinfo->oi_typcache[i]->typlen); + } + + /* "a" started empty, but "b" was not empty, so remember that */ + a->bt_empty_range = false; + + /* skip the per-key merge */ + MemoryContextDelete(cxt); + return; + } + + /* Now we know neither range is empty. */ for (keyno = 0; keyno < bdesc->bd_tupdesc->natts; keyno++) { FmgrInfo *unionFn; @@ -1711,7 +1780,9 @@ add_values_to_range(Relation idxRel, BrinDesc *bdesc, BrinMemTuple *dtup, Datum *values, bool *nulls) { int keyno; - bool modified = false; + + /* If the range starts empty, we're certainly going to modify it. */ + bool modified = dtup->bt_empty_range; /* * Compare the key values of the new tuple to the stored index values; our @@ -1725,9 +1796,24 @@ add_values_to_range(Relation idxRel, BrinDesc *bdesc, BrinMemTuple *dtup, Datum result; BrinValues *bval; FmgrInfo *addValue; + bool has_nulls; bval = &dtup->bt_columns[keyno]; + /* + * Does the range have actual NULL values? Either of the flags can + * be set, but we ignore the state before adding first row. + * + * We have to remember this, because we'll modify the flags and we + * need to know if the range started as empty. + */ + has_nulls = ((!dtup->bt_empty_range) && + (bval->bv_hasnulls || bval->bv_allnulls)); + + /* + * If the value we're adding is NULL, handle it locally. Otherwise + * call the BRIN_PROCNUM_ADDVALUE procedure. + */ if (bdesc->bd_info[keyno]->oi_regular_nulls && nulls[keyno]) { /* @@ -1753,8 +1839,33 @@ add_values_to_range(Relation idxRel, BrinDesc *bdesc, BrinMemTuple *dtup, nulls[keyno]); /* if that returned true, we need to insert the updated tuple */ modified |= DatumGetBool(result); + + /* + * If the range was had actual NULL values (i.e. did not start empty), + * make sure we don't forget about the NULL values. Either the allnulls + * flag is still set to true, or (if the opclass cleared it) we need to + * set hasnulls=true. + * + * XXX This can only happen when the opclass modified the tuple, so the + * modified flag should be set. + */ + if (has_nulls && !(bval->bv_hasnulls || bval->bv_allnulls)) + { + Assert(modified); + bval->bv_hasnulls = true; + } } + /* + * After updating summaries for all the keys, mark it as not empty. + * + * If we're actually changing the flag value (i.e. tuple started as empty), + * we should have modified the tuple. So we should not see empty range that + * was not modified. + */ + Assert(!dtup->bt_empty_range || modified); + dtup->bt_empty_range = false; + return modified; } diff --git a/src/backend/access/brin/brin_tuple.c b/src/backend/access/brin/brin_tuple.c index c0e2dbd23b..4a5a4da231 100644 --- a/src/backend/access/brin/brin_tuple.c +++ b/src/backend/access/brin/brin_tuple.c @@ -372,6 +372,9 @@ brin_form_tuple(BrinDesc *brdesc, BlockNumber blkno, BrinMemTuple *tuple, if (tuple->bt_placeholder) rettuple->bt_info |= BRIN_PLACEHOLDER_MASK; + if (tuple->bt_empty_range) + rettuple->bt_info |= BRIN_EMPTY_RANGE_MASK; + *size = len; return rettuple; } @@ -399,7 +402,7 @@ brin_form_placeholder_tuple(BrinDesc *brdesc, BlockNumber blkno, Size *size) rettuple = palloc0(len); rettuple->bt_blkno = blkno; rettuple->bt_info = hoff; - rettuple->bt_info |= BRIN_NULLS_MASK | BRIN_PLACEHOLDER_MASK; + rettuple->bt_info |= BRIN_NULLS_MASK | BRIN_PLACEHOLDER_MASK | BRIN_EMPTY_RANGE_MASK; bitP = ((bits8 *) ((char *) rettuple + SizeOfBrinTuple)) - 1; bitmask = HIGHBIT; @@ -489,6 +492,8 @@ brin_new_memtuple(BrinDesc *brdesc) dtup->bt_allnulls = palloc(sizeof(bool) * brdesc->bd_tupdesc->natts); dtup->bt_hasnulls = palloc(sizeof(bool) * brdesc->bd_tupdesc->natts); + dtup->bt_empty_range = true; + dtup->bt_context = AllocSetContextCreate(CurrentMemoryContext, "brin dtuple", ALLOCSET_DEFAULT_SIZES); @@ -527,6 +532,8 @@ brin_memtuple_initialize(BrinMemTuple *dtuple, BrinDesc *brdesc) currdatum += sizeof(Datum) * brdesc->bd_info[i]->oi_nstored; } + dtuple->bt_empty_range = true; + return dtuple; } @@ -560,6 +567,11 @@ brin_deform_tuple(BrinDesc *brdesc, BrinTuple *tuple, BrinMemTuple *dMemtuple) if (BrinTupleIsPlaceholder(tuple)) dtup->bt_placeholder = true; + + /* ranges start as empty, depends on the BrinTuple */ + if (!BrinTupleIsEmptyRange(tuple)) + dtup->bt_empty_range = false; + dtup->bt_blkno = tuple->bt_blkno; values = dtup->bt_values; diff --git a/src/include/access/brin_tuple.h b/src/include/access/brin_tuple.h index ced20d4543..634aa4b20e 100644 --- a/src/include/access/brin_tuple.h +++ b/src/include/access/brin_tuple.h @@ -44,6 +44,7 @@ typedef struct BrinValues typedef struct BrinMemTuple { bool bt_placeholder; /* this is a placeholder tuple */ + bool bt_empty_range; /* range represents no tuples */ BlockNumber bt_blkno; /* heap blkno that the tuple is for */ MemoryContext bt_context; /* memcxt holding the bt_columns values */ /* output arrays for brin_deform_tuple: */ @@ -69,7 +70,7 @@ typedef struct BrinTuple * * 7th (high) bit: has nulls * 6th bit: is placeholder tuple - * 5th bit: unused + * 5th bit: range is empty * 4-0 bit: offset of data * --------------- */ @@ -82,13 +83,14 @@ typedef struct BrinTuple * bt_info manipulation macros */ #define BRIN_OFFSET_MASK 0x1F -/* bit 0x20 is not used at present */ +#define BRIN_EMPTY_RANGE_MASK 0x20 #define BRIN_PLACEHOLDER_MASK 0x40 #define BRIN_NULLS_MASK 0x80 #define BrinTupleDataOffset(tup) ((Size) (((BrinTuple *) (tup))->bt_info & BRIN_OFFSET_MASK)) #define BrinTupleHasNulls(tup) (((((BrinTuple *) (tup))->bt_info & BRIN_NULLS_MASK)) != 0) #define BrinTupleIsPlaceholder(tup) (((((BrinTuple *) (tup))->bt_info & BRIN_PLACEHOLDER_MASK)) != 0) +#define BrinTupleIsEmptyRange(tup) (((((BrinTuple *) (tup))->bt_info & BRIN_EMPTY_RANGE_MASK)) != 0) extern BrinTuple *brin_form_tuple(BrinDesc *brdesc, BlockNumber blkno, diff --git a/src/test/modules/brin/expected/summarization-and-inprogress-insertion.out b/src/test/modules/brin/expected/summarization-and-inprogress-insertion.out index 2a4755d099..584ac2602f 100644 --- a/src/test/modules/brin/expected/summarization-and-inprogress-insertion.out +++ b/src/test/modules/brin/expected/summarization-and-inprogress-insertion.out @@ -4,7 +4,7 @@ starting permutation: s2check s1b s2b s1i s2summ s1c s2c s2check step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass); itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value ----------+------+------+--------+--------+-----------+-------- - 1| 0| 1|f |f |f |{1 .. 1} + 1| 0| 1|f |t |f |{1 .. 1} (1 row) step s1b: BEGIN ISOLATION LEVEL REPEATABLE READ; @@ -26,7 +26,7 @@ step s2c: COMMIT; step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass); itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value ----------+------+------+--------+--------+-----------+----------- - 1| 0| 1|f |f |f |{1 .. 1} + 1| 0| 1|f |t |f |{1 .. 1} 2| 1| 1|f |f |f |{1 .. 1000} (2 rows) @@ -35,7 +35,7 @@ starting permutation: s2check s1b s1i s2vacuum s1c s2check step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass); itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value ----------+------+------+--------+--------+-----------+-------- - 1| 0| 1|f |f |f |{1 .. 1} + 1| 0| 1|f |t |f |{1 .. 1} (1 row) step s1b: BEGIN ISOLATION LEVEL REPEATABLE READ; @@ -45,7 +45,7 @@ step s1c: COMMIT; step s2check: SELECT * FROM brin_page_items(get_raw_page('brinidx', 2), 'brinidx'::regclass); itemoffset|blknum|attnum|allnulls|hasnulls|placeholder|value ----------+------+------+--------+--------+-----------+----------- - 1| 0| 1|f |f |f |{1 .. 1} + 1| 0| 1|f |t |f |{1 .. 1} 2| 1| 1|f |f |f |{1 .. 1000} (2 rows) diff --git a/src/test/modules/brin/specs/summarization-and-inprogress-insertion.spec b/src/test/modules/brin/specs/summarization-and-inprogress-insertion.spec index 19ac18a2e8..18ba92b7ba 100644 --- a/src/test/modules/brin/specs/summarization-and-inprogress-insertion.spec +++ b/src/test/modules/brin/specs/summarization-and-inprogress-insertion.spec @@ -9,6 +9,7 @@ setup ) WITH (fillfactor=10); CREATE INDEX brinidx ON brin_iso USING brin (value) WITH (pages_per_range=1); -- this fills the first page + INSERT INTO brin_iso VALUES (NULL); DO $$ DECLARE curtid tid; BEGIN