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Add pg_column_toast_chunk_id().
This function returns the chunk_id of an on-disk TOASTed value. If the value is un-TOASTed or not on-disk, it returns NULL. This is useful for identifying which values are actually TOASTed and for investigating "unexpected chunk number" errors. Bumps catversion. Author: Yugo Nagata Reviewed-by: Jian He Discussion: https://postgr.es/m/20230329105507.d764497456eeac1ca491b5bd%40sraoss.co.jp
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6 files changed

+90
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‎doc/src/sgml/func.sgml

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@@ -28552,6 +28552,23 @@ postgres=# SELECT '0/0'::pg_lsn + pd.segment_number * ps.setting::int + :offset
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>
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<primary>pg_column_toast_chunk_id</primary>
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</indexterm>
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<function>pg_column_toast_chunk_id</function> ( <type>"any"</type> )
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<returnvalue>oid</returnvalue>
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</para>
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<para>
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Shows the <structfield>chunk_id</structfield> of an on-disk
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<acronym>TOAST</acronym>ed value. Returns <literal>NULL</literal>
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if the value is un-<acronym>TOAST</acronym>ed or not on-disk. See
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<xref linkend="storage-toast"/> for more information about
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<acronym>TOAST</acronym>.
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</para></entry>
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</row>
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<row>
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<entry role="func_table_entry"><para role="func_signature">
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<indexterm>

‎src/backend/utils/adt/varlena.c

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@@ -5105,6 +5105,47 @@ pg_column_compression(PG_FUNCTION_ARGS)
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PG_RETURN_TEXT_P(cstring_to_text(result));
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}
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/*
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* Return the chunk_id of the on-disk TOASTed value. Return NULL if the value
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* is un-TOASTed or not on-disk.
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*/
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Datum
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pg_column_toast_chunk_id(PG_FUNCTION_ARGS)
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{
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int typlen;
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struct varlena *attr;
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struct varatt_external toast_pointer;
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/* On first call, get the input type's typlen, and save at *fn_extra */
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if (fcinfo->flinfo->fn_extra == NULL)
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{
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/* Lookup the datatype of the supplied argument */
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Oid argtypeid = get_fn_expr_argtype(fcinfo->flinfo, 0);
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typlen = get_typlen(argtypeid);
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if (typlen == 0) /* should not happen */
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elog(ERROR, "cache lookup failed for type %u", argtypeid);
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fcinfo->flinfo->fn_extra = MemoryContextAlloc(fcinfo->flinfo->fn_mcxt,
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sizeof(int));
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*((int *) fcinfo->flinfo->fn_extra) = typlen;
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}
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else
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typlen = *((int *) fcinfo->flinfo->fn_extra);
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if (typlen != -1)
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PG_RETURN_NULL();
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attr = (struct varlena *) DatumGetPointer(PG_GETARG_DATUM(0));
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if (!VARATT_IS_EXTERNAL_ONDISK(attr))
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PG_RETURN_NULL();
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VARATT_EXTERNAL_GET_POINTER(toast_pointer, attr);
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PG_RETURN_OID(toast_pointer.va_valueid);
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}
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/*
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* string_agg - Concatenates values and returns string.
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*

‎src/include/catalog/catversion.h

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@@ -57,6 +57,6 @@
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*/
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/* yyyymmddN */
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#define CATALOG_VERSION_NO 202403132
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#define CATALOG_VERSION_NO 202403141
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#endif

‎src/include/catalog/pg_proc.dat

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@@ -7447,6 +7447,9 @@
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{ oid => '2121', descr => 'compression method for the compressed datum',
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proname => 'pg_column_compression', provolatile => 's', prorettype => 'text',
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proargtypes => 'any', prosrc => 'pg_column_compression' },
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{ oid => '8393', descr => 'chunk ID of on-disk TOASTed value',
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proname => 'pg_column_toast_chunk_id', provolatile => 's', prorettype => 'oid',
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proargtypes => 'any', prosrc => 'pg_column_toast_chunk_id' },
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{ oid => '2322',
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descr => 'total disk space usage for the specified tablespace',
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proname => 'pg_tablespace_size', provolatile => 'v', prorettype => 'int8',

‎src/test/regress/expected/misc_functions.out

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@@ -703,3 +703,19 @@ SELECT has_function_privilege('regress_current_logfile',
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(1 row)
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DROP ROLE regress_current_logfile;
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-- pg_column_toast_chunk_id
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CREATE TABLE test_chunk_id (a TEXT, b TEXT STORAGE EXTERNAL);
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INSERT INTO test_chunk_id VALUES ('x', repeat('x', 8192));
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SELECT t.relname AS toastrel FROM pg_class c
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LEFT JOIN pg_class t ON c.reltoastrelid = t.oid
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WHERE c.relname = 'test_chunk_id'
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\gset
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SELECT pg_column_toast_chunk_id(a) IS NULL,
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pg_column_toast_chunk_id(b) IN (SELECT chunk_id FROM pg_toast.:toastrel)
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FROM test_chunk_id;
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?column? | ?column?
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----------+----------
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t | t
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(1 row)
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DROP TABLE test_chunk_id;

‎src/test/regress/sql/misc_functions.sql

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@@ -265,3 +265,15 @@ GRANT pg_monitor TO regress_current_logfile;
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SELECT has_function_privilege('regress_current_logfile',
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'pg_current_logfile()', 'EXECUTE');
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DROP ROLE regress_current_logfile;
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-- pg_column_toast_chunk_id
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CREATE TABLE test_chunk_id (a TEXT, b TEXT STORAGE EXTERNAL);
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INSERT INTO test_chunk_id VALUES ('x', repeat('x', 8192));
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SELECT t.relname AS toastrel FROM pg_class c
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LEFT JOIN pg_class t ON c.reltoastrelid = t.oid
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WHERE c.relname = 'test_chunk_id'
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\gset
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SELECT pg_column_toast_chunk_id(a) IS NULL,
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pg_column_toast_chunk_id(b) IN (SELECT chunk_id FROM pg_toast.:toastrel)
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FROM test_chunk_id;
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DROP TABLE test_chunk_id;

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