Re: speedup COPY TO for partitioned table.

On Tue, 11 Mar 2025 at 18:24, jian he <jian(dot)universality(at)gmail(dot)com> wrote:
>
> after my change:
> ------------
> COPY TO can be used only with plain tables, not views, and does not
> copy rows from child tables,
> however COPY TO can be used with partitioned tables.
> For example, in a table inheritance hierarchy, COPY table TO copies
> the same rows as SELECT * FROM ONLY table.
> The syntax COPY (SELECT * FROM table) TO ... can be used to dump all
> of the rows in an inheritance hierarchy, or view.
> ------------

I find an issue with the patch:

-- Setup
CREATE SERVER myserver FOREIGN DATA WRAPPER postgres_fdw OPTIONS
(dbname 'testdb', port '5432');
CREATE TABLE t1(id int) PARTITION BY RANGE(id);
CREATE TABLE part1 PARTITION OF t1 FOR VALUES FROM (0) TO (5);
CREATE TABLE part2 PARTITION OF t1 FOR VALUES FROM (5) TO (15)
PARTITION BY RANGE(id);
CREATE FOREIGN TABLE part2_1 PARTITION OF part2 FOR VALUES FROM (10)
TO (15) SERVER myserver;

-- Create table in testdb
create table part2_1(id int);

-- Copy partitioned table data
postgres=# copy t1 to stdout(header);
server closed the connection unexpectedly
This probably means the server terminated abnormally
before or while processing the request.

Stack trace for the same is:
#0 table_beginscan (rel=0x72b109f9aad8, snapshot=0x5daafa77e000,
nkeys=0, key=0x0) at ../../../src/include/access/tableam.h:883
#1 0x00005daadf89eb9b in DoCopyTo (cstate=0x5daafa71e278) at copyto.c:1105
#2 0x00005daadf8913f4 in DoCopy (pstate=0x5daafa6c5fc0,
stmt=0x5daafa6f20c8, stmt_location=0, stmt_len=25,
processed=0x7ffd3799c2f0) at copy.c:316
#3 0x00005daadfc7a770 in standard_ProcessUtility
(pstmt=0x5daafa6f21e8, queryString=0x5daafa6f15c0 "copy t1 to
stdout(header);", readOnlyTree=false,
context=PROCESS_UTILITY_TOPLEVEL,
params=0x0, queryEnv=0x0, dest=0x5daafa6f25a8, qc=0x7ffd3799c660)
at utility.c:738

(gdb) f 0
#0 table_beginscan (rel=0x72b109f9aad8, snapshot=0x5daafa77e000,
nkeys=0, key=0x0) at ../../../src/include/access/tableam.h:883
883 return rel->rd_tableam->scan_begin(rel, snapshot, nkeys, key, NULL, flags);

The table access method is not available in this care
(gdb) p *rel->rd_tableam
Cannot access memory at address 0x0

This failure happens when we do table_beginscan on scan part2_1 table

Regards,
Vignesh