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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>55.10. Summary of Changes since Protocol 2.0</title><link rel="stylesheet" type="text/css" href="stylesheet.css" /><link rev="made" href="pgsql-docs@lists.postgresql.org" /><meta name="generator" content="DocBook XSL Stylesheets Vsnapshot" /><link rel="prev" href="protocol-logicalrep-message-formats.html" title="55.9. Logical Replication Message Formats" /><link rel="next" href="source.html" title="Chapter 56. PostgreSQL Coding Conventions" /></head><body id="docContent" class="container-fluid col-10"><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="5" align="center">55.10. Summary of Changes since Protocol 2.0</th></tr><tr><td width="10%" align="left"><a accesskey="p" href="protocol-logicalrep-message-formats.html" title="55.9. Logical Replication Message Formats">Prev</a> </td><td width="10%" align="left"><a accesskey="u" href="protocol.html" title="Chapter 55. Frontend/Backend Protocol">Up</a></td><th width="60%" align="center">Chapter 55. Frontend/Backend Protocol</th><td width="10%" align="right"><a accesskey="h" href="index.html" title="PostgreSQL 15.7 Documentation">Home</a></td><td width="10%" align="right"> <a accesskey="n" href="source.html" title="Chapter 56. PostgreSQL Coding Conventions">Next</a></td></tr></table><hr /></div><div class="sect1" id="PROTOCOL-CHANGES"><div class="titlepage"><div><div><h2 class="title" style="clear: both">55.10. Summary of Changes since Protocol 2.0</h2></div></div></div><p>
This section provides a quick checklist of changes, for the benefit of
developers trying to update existing client libraries to protocol 3.0.
</p><p>
The initial startup packet uses a flexible list-of-strings format
instead of a fixed format. Notice that session default values for run-time
parameters can now be specified directly in the startup packet. (Actually,
you could do that before using the <code class="literal">options</code> field, but given the
limited width of <code class="literal">options</code> and the lack of any way to quote
whitespace in the values, it wasn't a very safe technique.)
</p><p>
All messages now have a length count immediately following the message type
byte (except for startup packets, which have no type byte). Also note that
PasswordMessage now has a type byte.
</p><p>
ErrorResponse and NoticeResponse ('<code class="literal">E</code>' and '<code class="literal">N</code>')
messages now contain multiple fields, from which the client code can
assemble an error message of the desired level of verbosity. Note that
individual fields will typically not end with a newline, whereas the single
string sent in the older protocol always did.
</p><p>
The ReadyForQuery ('<code class="literal">Z</code>') message includes a transaction status
indicator.
</p><p>
The distinction between BinaryRow and DataRow message types is gone; the
single DataRow message type serves for returning data in all formats.
Note that the layout of DataRow has changed to make it easier to parse.
Also, the representation of binary values has changed: it is no longer
directly tied to the server's internal representation.
</p><p>
There is a new <span class="quote">“<span class="quote">extended query</span>”</span> sub-protocol, which adds the frontend
message types Parse, Bind, Execute, Describe, Close, Flush, and Sync, and the
backend message types ParseComplete, BindComplete, PortalSuspended,
ParameterDescription, NoData, and CloseComplete. Existing clients do not
have to concern themselves with this sub-protocol, but making use of it
might allow improvements in performance or functionality.
</p><p>
<code class="command">COPY</code> data is now encapsulated into CopyData and CopyDone messages. There
is a well-defined way to recover from errors during <code class="command">COPY</code>. The special
<span class="quote">“<span class="quote"><code class="literal">\.</code></span>”</span> last line is not needed anymore, and is not sent
during <code class="command">COPY OUT</code>.
(It is still recognized as a terminator during <code class="command">COPY IN</code>, but its use is
deprecated and will eventually be removed.) Binary <code class="command">COPY</code> is supported.
The CopyInResponse and CopyOutResponse messages include fields indicating
the number of columns and the format of each column.
</p><p>
The layout of FunctionCall and FunctionCallResponse messages has changed.
FunctionCall can now support passing NULL arguments to functions. It also
can handle passing parameters and retrieving results in either text or
binary format. There is no longer any reason to consider FunctionCall a
potential security hole, since it does not offer direct access to internal
server data representations.
</p><p>
The backend sends ParameterStatus ('<code class="literal">S</code>') messages during connection
startup for all parameters it considers interesting to the client library.
Subsequently, a ParameterStatus message is sent whenever the active value
changes for any of these parameters.
</p><p>
The RowDescription ('<code class="literal">T</code>') message carries new table OID and column
number fields for each column of the described row. It also shows the format
code for each column.
</p><p>
The CursorResponse ('<code class="literal">P</code>') message is no longer generated by
the backend.
</p><p>
The NotificationResponse ('<code class="literal">A</code>') message has an additional string
field, which can carry a <span class="quote">“<span class="quote">payload</span>”</span> string passed
from the <code class="command">NOTIFY</code> event sender.
</p><p>
The EmptyQueryResponse ('<code class="literal">I</code>') message used to include an empty
string parameter; this has been removed.
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