@@ -618,13 +618,16 @@ HINT: Stop the postmaster and use a standalone backend to VACUUM in "mydb".
618618 </indexterm>
619619
620620 <para>
621- <firstterm>Multixacts</> are used to implement row locking by
622- multiple transactions: since there is limited space in the tuple
623- header to store lock information, that information is stored as a
624- multixact separately in the <filename>pg_multixact</> subdirectory,
625- and only its ID is in the <structfield>xmax</> field
626- in the tuple header.
627- Similar to transaction IDs, multixact IDs are implemented as a
621+ <firstterm>Multixact IDs</> are used to support row locking by
622+ multiple transactions. Since there is only limited space in a tuple
623+ header to store lock information, that information is encoded as
624+ a <quote>multiple transaction ID</>, or multixact ID for short,
625+ whenever there is more than one transaction concurrently locking a
626+ row. Information about which transaction IDs are included in any
627+ particular multixact ID is stored separately in
628+ the <filename>pg_multixact</> subdirectory, and only the multixact ID
629+ appears in the <structfield>xmax</> field in the tuple header.
630+ Like transaction IDs, multixact IDs are implemented as a
628631 32-bit counter and corresponding storage, all of which requires
629632 careful aging management, storage cleanup, and wraparound handling.
630633 </para>
@@ -636,8 +639,8 @@ HINT: Stop the postmaster and use a standalone backend to VACUUM in "mydb".
636639 is replaced by a different value, which can be the zero value, a single
637640 transaction ID, or a newer multixact ID. For each table,
638641 <structname>pg_class</>.<structfield>relminmxid</> stores the oldest
639- possiblevalue stillstored in any tuple of that table. Every time this
640- value is older than
642+ possiblemultixact ID stillappearing in any tuple of that table.
643+ If this value is older than
641644 <xref linkend="guc-vacuum-multixact-freeze-table-age">, a whole-table
642645 scan is forced. Whole-table <command>VACUUM</> scans, regardless of
643646 what causes them, enable advancing the value for that table.