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I attach a version of my toast-slicing patch, against current CVS

Browse Source 
(current as of a few hours ago.)

This patch:

1. Adds PG_GETARG_xxx_P_SLICE() macros and associated support routines.

2. Adds routines in src/backend/access/tuptoaster.c for fetching only
necessary chunks of a toasted value. (Modelled on latest changes to
assume chunks are returned in order).

3. Amends text_substr and bytea_substr to use new methods. It now
handles multibyte cases -and should still lead to a performance
improvement in the multibyte case where the substring is near the
beginning of the string.

4. Added new command: ALTER TABLE tabname ALTER COLUMN colname SET
STORAGE {PLAIN | EXTERNAL | EXTENDED | MAIN} to parser and documented in
alter-table.sgml. (NB I used ColId as the item type for the storage
mode string, rather than a new production - I hope this makes sense!).
All this does is sets attstorage for the specified column.

4. AlterTableAlterColumnStatistics is now AlterTableAlterColumnFlags and
handles both statistics and storage (it uses the subtype code to
distinguish). The previous version of my patch also re-arranged other
code in backend/commands/command.c but I have dropped that from this
patch.(I plan to return to it separately).

5. Documented new macros (and also the PG_GETARG_xxx_P_COPY macros) in
xfunc.sgml. ref/alter_table.sgml also contains documentation for ALTER
COLUMN SET STORAGE.

John Gray
This commit is contained in:
Bruce Momjian
2002-03-05 05:33:31 +00:00
parent 276fc7ce82
commit 03194432de
13 changed files with 498 additions and 79 deletions
Download Patch File Download Diff File Expand all files Collapse all files

87
src/backend/utils/adt/varlena.c
View File

@ -8,7 +8,7 @@
*
*
* IDENTIFICATION
* $Header: /cvsroot/pgsql/src/backend/utils/adt/varlena.c,v 1.78 2001/11/19 19:15:07 momjian Exp $
* $Header: /cvsroot/pgsql/src/backend/utils/adt/varlena.c,v 1.79 2002/03/05 05:33:19 momjian Exp $
*
*-------------------------------------------------------------------------
*/
@ -332,49 +332,71 @@ textcat(PG_FUNCTION_ARGS)
* Changed behavior if starting position is less than one to conform to SQL92 behavior.
* Formerly returned the entire string; now returns a portion.
* - Thomas Lockhart 1998-12-10
* Now uses faster TOAST-slicing interface
* - John Gray 2002-02-22
*/
Datum
text_substr(PG_FUNCTION_ARGS)
{
text *string = PG_GETARG_TEXT_P(0);
text *string;
int32 m = PG_GETARG_INT32(1);
int32 n = PG_GETARG_INT32(2);
text *ret;
int len;
int32 sm;
int32 sn;
int eml = 1;
#ifdef MULTIBYTE
int i;
int len;
text *ret;
char *p;
#endif
len = VARSIZE(string) - VARHDRSZ;
#ifdef MULTIBYTE
len = pg_mbstrlen_with_len(VARDATA(string), len);
#endif
/* starting position after the end of the string? */
if (m > len)
{
m = 1;
n = 0;
}
#endif
/*
* starting position before the start of the string? then offset into
* the string per SQL92 spec...
*/
else if (m < 1)
if (m < 1)
{
n += (m - 1);
m = 1;
}
/* Check for m > octet length is made in TOAST access routine */
/* m will now become a zero-based starting position */
sm = m - 1;
sn = n;
#ifdef MULTIBYTE
eml = pg_database_encoding_max_length ();
if (eml > 1)
{
sm = 0;
sn = (m + n) * eml + 3; /* +3 to avoid mb characters overhanging slice end */
}
#endif
string = PG_GETARG_TEXT_P_SLICE (0, sm, sn);
if (eml == 1)
{
PG_RETURN_TEXT_P (string);
}
#ifndef MULTIBYTE
PG_RETURN_NULL(); /* notreached: suppress compiler warning */
#endif
#ifdef MULTIBYTE
len = pg_mbstrlen_with_len (VARDATA (string), sn - 3);
if (m > len)
{
m = 1;
n = 0;
}
m--;
if (((m + n) > len) || (n < 0))
n = (len - m);
#ifdef MULTIBYTE
p = VARDATA(string);
for (i = 0; i < m; i++)
p += pg_mblen(p);
@ -382,7 +404,6 @@ text_substr(PG_FUNCTION_ARGS)
for (i = 0; i < n; i++)
p += pg_mblen(p);
n = p - (VARDATA(string) + m);
#endif
ret = (text *) palloc(VARHDRSZ + n);
VARATT_SIZEP(ret) = VARHDRSZ + n;
@ -390,6 +411,7 @@ text_substr(PG_FUNCTION_ARGS)
memcpy(VARDATA(ret), VARDATA(string) + m, n);
PG_RETURN_TEXT_P(ret);
#endif
}
/*
@ -740,26 +762,14 @@ byteacat(PG_FUNCTION_ARGS)
Datum
bytea_substr(PG_FUNCTION_ARGS)
{
bytea *string = PG_GETARG_BYTEA_P(0);
int32 m = PG_GETARG_INT32(1);
int32 n = PG_GETARG_INT32(2);
bytea *ret;
int len;
len = VARSIZE(string) - VARHDRSZ;
/* starting position after the end of the string? */
if (m > len)
{
m = 1;
n = 0;
}
/*
* starting position before the start of the string? then offset into
* the string per SQL92 spec...
*/
else if (m < 1)
if (m < 1)
{
n += (m - 1);
m = 1;
@ -767,15 +777,8 @@ bytea_substr(PG_FUNCTION_ARGS)
/* m will now become a zero-based starting position */
m--;
if (((m + n) > len) || (n < 0))
n = (len - m);
ret = (bytea *) palloc(VARHDRSZ + n);
VARATT_SIZEP(ret) = VARHDRSZ + n;
memcpy(VARDATA(ret), VARDATA(string) + m, n);
PG_RETURN_BYTEA_P(ret);
PG_RETURN_BYTEA_P(PG_GETARG_BYTEA_P_SLICE (0, m, n));
}
/*