database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-05 07:21:24 +03:00
Code Activity

Add a transform function for numeric typmod coercisions.

Browse Source 
This enables ALTER TABLE to skip table and index rebuilds when a column
is changed to an unconstrained numeric, or when the scale is unchanged
and the precision does not decrease.

Noah Misch, with a few stylistic changes and a fix for an OID
collision by me.
This commit is contained in:
Robert Haas
2012-02-07 12:08:26 -05:00
parent af7914c662
commit 3cc0800829
4 changed files with 53 additions and 2 deletions
Download Patch File Download Diff File Expand all files Collapse all files

48
src/backend/utils/adt/numeric.c
View File

@ -30,6 +30,8 @@
#include "catalog/pg_type.h"
#include "libpq/pqformat.h"
#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_clause.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/int8.h"
@ -712,6 +714,52 @@ numeric_send(PG_FUNCTION_ARGS)
}
/*
* numeric_transform() -
*
* Flatten calls to our length coercion function that solely represent
* increases in allowable precision. Scale changes mutate every datum, so
* they are unoptimizable. Some values, e.g. 1E-1001, can only fit into an
* unconstrained numeric, so a change from an unconstrained numeric to any
* constrained numeric is also unoptimizable.
*/
Datum
numeric_transform(PG_FUNCTION_ARGS)
{
FuncExpr *expr = (FuncExpr *) PG_GETARG_POINTER(0);
Node *typmod;
Node *ret = NULL;
if (!IsA(expr, FuncExpr))
PG_RETURN_POINTER(ret);
Assert(list_length(expr->args) == 2);
typmod = lsecond(expr->args);
if (IsA(typmod, Const))
{
Node *source = linitial(expr->args);
int32 old_typmod = exprTypmod(source);
int32 new_typmod = DatumGetInt32(((Const *) typmod)->constvalue);
int32 old_scale = (old_typmod - VARHDRSZ) & 0xffff;
int32 new_scale = (new_typmod - VARHDRSZ) & 0xffff;
int32 old_precision = (old_typmod - VARHDRSZ) >> 16 & 0xffff;
int32 new_precision = (new_typmod - VARHDRSZ) >> 16 & 0xffff;
/*
* If new_typmod < VARHDRSZ, the destination is unconstrained; that's
* always OK. If old_typmod >= VARHDRSZ, the source is constained.
* and we're OK if the scale is unchanged and the precison is not
* decreasing. See further nodes in function header comment.
*/
if (new_typmod < VARHDRSZ || (old_typmod >= VARHDRSZ &&
new_scale == old_scale && new_precision >= old_precision))
ret = relabel_to_typmod(source, new_typmod);
}
PG_RETURN_POINTER(ret);
}
/*
* numeric() -
*