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Fix mvdistinct and dependencies size calculations

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The formulas used to calculate size while (de)serializing mvndistinct
and functional dependencies were based on offset() of the structs. But
that is incorrect, because the structures are not copied directly, we
we copy the individual fields directly.

At the moment this works fine, because there is no alignment padding
on any platform we support. But it might break if we ever added some
fields into any of the structs, for example. It's also confusing.

Fixed by reworking the macros to directly sum sizes of serialized
fields. The macros are now useful only for serialiation, so there is
no point in keeping them in the public header file. So make them
private by moving them to the .c files.

Also adds a couple more asserts to check the serialization, and fixes
an incorrect allocation of MVDependency instead of (MVDependency *).

Reported-By: Tom Lane
Discussion: https://postgr.es/m/29785.1555365602@sss.pgh.pa.us
This commit is contained in:
Tomas Vondra
2019-04-21 19:54:15 +02:00
parent bfbc150e39
commit d08c44f7a4
3 changed files with 56 additions and 40 deletions
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37
src/backend/statistics/mvdistinct.c
View File

@@ -43,6 +43,20 @@ static double estimate_ndistinct(double totalrows, int numrows, int d, int f1);
static int n_choose_k(int n, int k);
static int num_combinations(int n);
/* size of the struct header fields (magic, type, nitems) */
#define SizeOfHeader (3 * sizeof(uint32))
/* size of a serialized ndistinct item (coefficient, natts, atts) */
#define SizeOfItem(natts) \
(sizeof(double) + sizeof(int) + (natts) * sizeof(AttrNumber))
/* minimal size of a ndistinct item (with two attributes) */
#define MinSizeOfItem SizeOfItem(2)
/* minimal size of mvndistinct, when all items are minimal */
#define MinSizeOfItems(nitems) \
(SizeOfHeader + (nitems) * MinSizeOfItem)
/* Combination generator API */
/* internal state for generator of k-combinations of n elements */
@@ -168,8 +182,7 @@ statext_ndistinct_serialize(MVNDistinct *ndistinct)
* Base size is size of scalar fields in the struct, plus one base struct
* for each item, including number of items for each.
*/
len = VARHDRSZ + SizeOfMVNDistinct +
ndistinct->nitems * (offsetof(MVNDistinctItem, attrs) + sizeof(int));
len = VARHDRSZ + SizeOfHeader;
/* and also include space for the actual attribute numbers */
for (i = 0; i < ndistinct->nitems; i++)
@@ -178,7 +191,8 @@ statext_ndistinct_serialize(MVNDistinct *ndistinct)
nmembers = bms_num_members(ndistinct->items[i].attrs);
Assert(nmembers >= 2);
len += sizeof(AttrNumber) * nmembers;
len += SizeOfItem(nmembers);
}
output = (bytea *) palloc(len);
@@ -195,8 +209,7 @@ statext_ndistinct_serialize(MVNDistinct *ndistinct)
tmp += sizeof(uint32);
/*
* store number of attributes and attribute numbers for each ndistinct
* entry
* store number of attributes and attribute numbers for each entry
*/
for (i = 0; i < ndistinct->nitems; i++)
{
@@ -218,9 +231,13 @@ statext_ndistinct_serialize(MVNDistinct *ndistinct)
tmp += sizeof(AttrNumber);
}
/* protect against overflows */
Assert(tmp <= ((char *) output + len));
}
/* check we used exactly the expected space */
Assert(tmp == ((char *) output + len));
return output;
}
@@ -241,9 +258,9 @@ statext_ndistinct_deserialize(bytea *data)
return NULL;
/* we expect at least the basic fields of MVNDistinct struct */
if (VARSIZE_ANY_EXHDR(data) < SizeOfMVNDistinct)
if (VARSIZE_ANY_EXHDR(data) < SizeOfHeader)
elog(ERROR, "invalid MVNDistinct size %zd (expected at least %zd)",
VARSIZE_ANY_EXHDR(data), SizeOfMVNDistinct);
VARSIZE_ANY_EXHDR(data), SizeOfHeader);
/* initialize pointer to the data part (skip the varlena header) */
tmp = VARDATA_ANY(data);
@@ -272,9 +289,7 @@ statext_ndistinct_deserialize(bytea *data)
errmsg("invalid zero-length item array in MVNDistinct")));
/* what minimum bytea size do we expect for those parameters */
minimum_size = (SizeOfMVNDistinct +
ndist.nitems * (SizeOfMVNDistinctItem +
sizeof(AttrNumber) * 2));
minimum_size = MinSizeOfItems(ndist.nitems);
if (VARSIZE_ANY_EXHDR(data) < minimum_size)
ereport(ERROR,
(errcode(ERRCODE_DATA_CORRUPTED),
@@ -285,7 +300,7 @@ statext_ndistinct_deserialize(bytea *data)
* Allocate space for the ndistinct items (no space for each item's
* attnos: those live in bitmapsets allocated separately)
*/
ndistinct = palloc0(MAXALIGN(SizeOfMVNDistinct) +
ndistinct = palloc0(MAXALIGN(offsetof(MVNDistinct, items)) +
(ndist.nitems * sizeof(MVNDistinctItem)));
ndistinct->magic = ndist.magic;
ndistinct->type = ndist.type;