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Re-order pg_attribute columns to eliminate some padding space.

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Now that attcompression is just a char, there's a lot of wasted
padding space after it.  Move it into the group of char-wide
columns to save a net of 4 bytes per pg_attribute entry.  While
we're at it, swap the order of attstorage and attalign to make for
a more logical grouping of these columns.

Also re-order actions in related code to match the new field ordering.

This patch also fixes one outright bug: equalTupleDescs() failed to
compare attcompression.  That could, for example, cause relcache
reload to fail to adopt a new value following a change.

Michael Paquier and Tom Lane, per a gripe from Andres Freund.

Discussion: https://postgr.es/m/20210517204803.iyk5wwvwgtjcmc5w@alap3.anarazel.de
This commit is contained in:
Tom Lane
2021-05-23 12:12:09 -04:00
parent bc2a389efb
commit f5024d8d7b
11 changed files with 80 additions and 74 deletions
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28
doc/src/sgml/catalogs.sgml
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@ -1236,6 +1236,15 @@
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>attalign</structfield> <type>char</type>
</para>
<para>
A copy of <literal>pg_type.typalign</literal> of this column's type
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>attstorage</structfield> <type>char</type>
@ -1249,10 +1258,13 @@
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>attalign</structfield> <type>char</type>
<structfield>attcompression</structfield> <type>char</type>
</para>
<para>
A copy of <literal>pg_type.typalign</literal> of this column's type
The current compression method of the column. If it is an invalid
compression method (<literal>'\0'</literal>) then column data will not
be compressed. Otherwise, <literal>'p'</literal> = pglz compression or
<literal>'l'</literal> = <productname>LZ4</productname> compression.
</para></entry>
</row>
@ -1355,18 +1367,6 @@
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>attcompression</structfield> <type>char</type>
</para>
<para>
The current compression method of the column. If it is an invalid
compression method (<literal>'\0'</literal>) then column data will not
be compressed. Otherwise, <literal>'p'</literal> = pglz compression or
<literal>'l'</literal> = <productname>LZ4</productname> compression.
</para></entry>
</row>
<row>
<entry role="catalog_table_entry"><para role="column_definition">
<structfield>attacl</structfield> <type>aclitem[]</type>