Feedback-ID: i0fe9450f:Fastmail
Date: Thu, 20 Jul 2023 12:07:14 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Tristan Partin <tristan@neon.tech>
Cc: pgsql-hackers@postgresql.org
Subject: Re: Use COPY for populating all pgbench tables
Message-ID: <ZLik4oKnqRmVCM3t@paquier.xyz>
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On Wed, Jul 19, 2023 at 01:03:21PM -0500, Tristan Partin wrote:
> Didn't actually include the changes in the previous patch.

-initGenerateDataClientSide(PGconn *con)
+initBranch(PQExpBufferData *sql, int64 curr)
 {
-   PQExpBufferData sql;
+   /* "filler" column defaults to NULL */
+   printfPQExpBuffer(sql,
+                     INT64_FORMAT "\t0\t\n",
+                     curr + 1);
+}
+
+static void
+initTeller(PQExpBufferData *sql, int64 curr)
+{
+   /* "filler" column defaults to NULL */
+   printfPQExpBuffer(sql,
+                     INT64_FORMAT "\t" INT64_FORMAT "\t0\t\n",
+                     curr + 1, curr / ntellers + 1);

Hmm.  Something's not right here, see:
=3D# select count(*) has_nulls from pgbench_accounts where filler is null;
 has_nulls=20
-----------
         0
(1 row)
=3D# select count(*) > 0 has_nulls from pgbench_tellers where filler is nul=
l;
 has_nulls=20
-----------
 f
(1 row)
=3D# select count(*) > 0 has_nulls from pgbench_branches where filler is nu=
ll;
 has_nulls=20
-----------
 f
(1 row)

Note as well this comment in initCreateTables():
    /*
     * Note: TPC-B requires at least 100 bytes per row, and the "filler"
     * fields in these table declarations were intended to comply with that.
     * The pgbench_accounts table complies with that because the "filler"
     * column is set to blank-padded empty string. But for all other tables
     * the columns default to NULL and so don't actually take any space.  We
     * could fix that by giving them non-null default values.  However, that
     * would completely break comparability of pgbench results with prior
     * versions. Since pgbench has never pretended to be fully TPC-B compli=
ant
     * anyway, we stick with the historical behavior.
     */

So this patch causes pgbench to not stick with its historical
behavior, and the change is incompatible with the comments because the
tellers and branches tables don't use NULL for their filler attribute
anymore.
--
Michael

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