On Tue, 2 Jan 2024 08:00:00 +0800
jian he <jian.universal...@gmail.com> wrote:
> On Mon, Nov 6, 2023 at 8:00 AM jian he <jian.universal...@gmail.com> wrote:
> >
> > minor doc issues.
> > Returns the chunk id of the TOASTed value, or NULL if the value is not
> > TOASTed.
> > Should it be "chunk_id"?
Thank you for your suggestion. As you pointed out, it is called "chunk_id"
in the documentation, so I rewrote it and also added a link to the section
where the TOAST table structure is explained.
> > you may place it after pg_create_logical_replication_slot entry to
> > make it look like alphabetical order.
I've been thinking about where we should place the function in the doc,
and I decided place it in the table of Database Object Size Functions
because I think pg_column_toast_chunk_id also would assist understanding
the result of size functions as similar to pg_column_compression; that is,
those function can explain why a large value in size could be stored in
a column.
> > There is no test. maybe we can add following to
> > src/test/regress/sql/misc.sql
> > create table val(t text);
> > INSERT into val(t) SELECT string_agg(
> > chr((ascii('B') + round(random() * 25)) :: integer),'')
> > FROM generate_series(1,2500);
> > select pg_column_toast_chunk_id(t) is not null from val;
> > drop table val;
Thank you for the test proposal. However, if we add a test, I want
to check that the chunk_id returned by the function exists in the
TOAST table, and that it returns NULL if the values is not TOASTed.
For the purpose, I wrote a test using a dynamic SQL since the table
name of the TOAST table have to be generated from the main table's OID.
> Hi
> the main C function (pg_column_toast_chunk_id) I didn't change.
> I added tests as mentioned above.
> tests put it on src/test/regress/sql/misc.sql, i hope that's fine.
> I placed pg_column_toast_chunk_id in "Table 9.99. Database Object
> Location Functions" (below Table 9.98. Database Object Size
> Functions).
I could not find any change in your patch from my previous patch.
Maybe, you attached wrong file. I attached a patch updated based
on your review, including the documentation fixes and a test.
What do you think about this it?
Regards,
Yugo Nagata
--
Yugo NAGATA <nag...@sraoss.co.jp>
>From 97af1b2300ecf07a34923da87a9d84e6aa963956 Mon Sep 17 00:00:00 2001
From: Yugo Nagata <nag...@sraoss.co.jp>
Date: Wed, 29 Mar 2023 09:59:25 +0900
Subject: [PATCH v3] Add pg_column_toast_chunk_id function
This function returns the chunk_id of an on-disk TOASTed value, or
NULL if the value is un-TOASTed or not on disk. This enables users to
know which columns are actually TOASTed. This function is also useful
to identify a problematic row when an error like
"ERROR: unexpected chunk number ... (expected ...) for toast value"
occurs.
---
doc/src/sgml/func.sgml | 17 ++++++++++++++
src/backend/utils/adt/varlena.c | 41 +++++++++++++++++++++++++++++++++
src/include/catalog/pg_proc.dat | 3 +++
3 files changed, 61 insertions(+)
diff --git a/doc/src/sgml/func.sgml b/doc/src/sgml/func.sgml
index 210c7c0b02..2d82331323 100644
--- a/doc/src/sgml/func.sgml
+++ b/doc/src/sgml/func.sgml
@@ -28078,6 +28078,23 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
</para></entry>
</row>
+ <row>
+ <entry role="func_table_entry"><para role="func_signature">
+ <indexterm>
+ <primary>pg_column_toast_chunk_id</primary>
+ </indexterm>
+ <function>pg_column_toast_chunk_id</function> ( <type>"any"</type> )
+ <returnvalue>oid</returnvalue>
+ </para>
+ <para>
+ Shows the <structfield>chunk_id</structfield> of an on-disk
+ <acronym>TOAST</acronym>ed value. Returns <literal>NULL</literal>
+ if the value is un-<acronym>TOAST</acronym>ed or not on-disk.
+ See <xref linkend="storage-toast-ondisk"/> for details about
+ <acronym>TOAST</acronym>.
+ </para></entry>
+ </row>
+
<row>
<entry role="func_table_entry"><para role="func_signature">
<indexterm>
diff --git a/src/backend/utils/adt/varlena.c b/src/backend/utils/adt/varlena.c
index 543afb66e5..84d36781a4 100644
--- a/src/backend/utils/adt/varlena.c
+++ b/src/backend/utils/adt/varlena.c
@@ -5105,6 +5105,47 @@ pg_column_compression(PG_FUNCTION_ARGS)
PG_RETURN_TEXT_P(cstring_to_text(result));
}
+/*
+ * Return the chunk_id of the on-disk TOASTed value.
+ * Return NULL if the value is unTOASTed or not on disk.
+ */
+Datum
+pg_column_toast_chunk_id(PG_FUNCTION_ARGS)
+{
+ int typlen;
+ struct varlena *attr;
+ struct varatt_external toast_pointer;
+
+ /* On first call, get the input type's typlen, and save at *fn_extra */
+ if (fcinfo->flinfo->fn_extra == NULL)
+ {
+ /* Lookup the datatype of the supplied argument */
+ Oid argtypeid = get_fn_expr_argtype(fcinfo->flinfo, 0);
+
+ typlen = get_typlen(argtypeid);
+ if (typlen == 0) /* should not happen */
+ elog(ERROR, "cache lookup failed for type %u", argtypeid);
+
+ fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
+ sizeof(int));
+ *((int *) fcinfo->flinfo->fn_extra) = typlen;
+ }
+ else
+ typlen = *((int *) fcinfo->flinfo->fn_extra);
+
+ if (typlen != -1)
+ PG_RETURN_NULL();
+
+ attr = (struct varlena *) DatumGetPointer(PG_GETARG_DATUM(0));
+
+ if (!VARATT_IS_EXTERNAL_ONDISK(attr))
+ PG_RETURN_NULL();
+
+ VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
+
+ PG_RETURN_OID(toast_pointer.va_valueid);
+}
+
/*
* string_agg - Concatenates values and returns string.
*
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index 58811a6530..1d4521ac1f 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -7454,6 +7454,9 @@
{ oid => '2121', descr => 'compression method for the compressed datum',
proname => 'pg_column_compression', provolatile => 's', prorettype => 'text',
proargtypes => 'any', prosrc => 'pg_column_compression' },
+{ oid => '8393', descr => 'chunk ID of on-disk TOASTed value',
+ proname => 'pg_column_toast_chunk_id', provolatile => 's', prorettype => 'oid',
+ proargtypes => 'any', prosrc => 'pg_column_toast_chunk_id' },
{ oid => '2322',
descr => 'total disk space usage for the specified tablespace',
proname => 'pg_tablespace_size', provolatile => 'v', prorettype => 'int8',
--
2.25.1
