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postgresql9.6-docs-9.6.17-2.mga7.noarch.rpm

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>33.2. Implementation Features</A
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>    The large object implementation breaks large
    objects up into <SPAN
CLASS="QUOTE"
>"chunks"</SPAN
> and stores the chunks in
    rows in the database.  A B-tree index guarantees fast
    searches for the correct chunk number when doing random
    access reads and writes.
   </P
><P
>    The chunks stored for a large object do not have to be contiguous.
    For example, if an application opens a new large object, seeks to offset
    1000000, and writes a few bytes there, this does not result in allocation
    of 1000000 bytes worth of storage; only of chunks covering the range of
    data bytes actually written.  A read operation will, however, read out
    zeroes for any unallocated locations preceding the last existing chunk.
    This corresponds to the common behavior of <SPAN
CLASS="QUOTE"
>"sparsely allocated"</SPAN
>
    files in <ACRONYM
CLASS="ACRONYM"
>Unix</ACRONYM
> file systems.
   </P
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>    As of <SPAN
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>PostgreSQL</SPAN
> 9.0, large objects have an owner
    and a set of access permissions, which can be managed using
    <A
HREF="sql-grant.html"
>GRANT</A
> and
    <A
HREF="sql-revoke.html"
>REVOKE</A
>.
    <TT
CLASS="LITERAL"
>SELECT</TT
> privileges are required to read a large
    object, and
    <TT
CLASS="LITERAL"
>UPDATE</TT
> privileges are required to write or
    truncate it.
    Only the large object's owner (or a database superuser) can delete,
    comment on, or change the owner of a large object.
    To adjust this behavior for compatibility with prior releases, see the
    <A
HREF="runtime-config-compatible.html#GUC-LO-COMPAT-PRIVILEGES"
>lo_compat_privileges</A
> run-time parameter.
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