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Commit69cf1d5

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Add PQsendFlushRequest to libpq
This new libpq function allows the application to send an 'H' message,which instructs the server to flush its outgoing buffer.This hasn't been needed so far because the Sync message already requestsa buffer; and I failed to realize that this was needed in pipeline modebecause PQpipelineSync also causes the buffer to be flushed. However,sometimes it is useful to request a flush without establishing asynchronization point.Backpatch to 14, where pipeline mode was introduced in libpq.Reported-by: Boris Kolpackov <boris@codesynthesis.com>Author: Álvaro Herrera <alvherre@alvh.no-ip.org>Discussion:https://postgr.es/m/202106252350.t76x73nt643j@alvherre.pgsql
1 parentf8b5146 commit69cf1d5

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4 files changed

+70
-3
lines changed

4 files changed

+70
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lines changed

‎doc/src/sgml/libpq.sgml

Lines changed: 31 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -5102,10 +5102,13 @@ int PQflush(PGconn *conn);
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The server executes statements, and returns results, in the order the
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client sends them. The server will begin executing the commands in the
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pipeline immediately, not waiting for the end of the pipeline.
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Note that results are buffered on the server side; the server flushes
5106+
that buffer when a synchronization point is established with
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<function>PQpipelineSync</function>, or when
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<function>PQsendFlushRequest</function> is called.
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If any statement encounters an error, the server aborts the current
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transaction and does not execute any subsequent command in the queue
5107-
until the next synchronization point established by
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<function>PQpipelineSync</function>;
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until the next synchronization point;
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a <literal>PGRES_PIPELINE_ABORTED</literal> result is produced for
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each such command.
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(This remains true even if the commands in the pipeline would rollback
@@ -5399,6 +5402,32 @@ int PQpipelineSync(PGconn *conn);
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="libpq-PQsendFlushRequest">
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<term><function>PQsendFlushRequest</function><indexterm><primary>PQsendFlushRequest</primary></indexterm></term>
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<listitem>
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<para>
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Sends a request for the server to flush its output buffer.
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<synopsis>
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int PQsendFlushRequest(PGconn *conn);
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</synopsis>
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</para>
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<para>
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Returns 1 for success. Returns 0 on any failure.
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</para>
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<para>
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The server flushes its output buffer automatically as a result of
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<function>PQpipelineSync</function> being called, or
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on any request when not in pipeline mode; this function is useful
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to cause the server to flush its output buffer in pipeline mode
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without establishing a synchronization point.
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Note that the request is not itself flushed to the server automatically;
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use <function>PQflush</function> if necessary.
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</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</sect2>
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‎src/interfaces/libpq/exports.txt

Lines changed: 2 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -184,4 +184,5 @@ PQexitPipelineMode 181
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PQpipelineSync 182
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PQpipelineStatus 183
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PQsetTraceFlags 184
187-
PQmblenBounded 185
187+
PQmblenBounded 185
188+
PQsendFlushRequest 186

‎src/interfaces/libpq/fe-exec.c

Lines changed: 36 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -3099,6 +3099,42 @@ PQpipelineSync(PGconn *conn)
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return0;
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}
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/*
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* PQsendFlushRequest
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*Send request for server to flush its buffer. Useful in pipeline
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*mode when a sync point is not desired.
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*/
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int
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PQsendFlushRequest(PGconn*conn)
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{
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if (!conn)
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return0;
3112+
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/* Don't try to send if we know there's no live connection. */
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if (conn->status!=CONNECTION_OK)
3115+
{
3116+
appendPQExpBufferStr(&conn->errorMessage,
3117+
libpq_gettext("no connection to the server\n"));
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return0;
3119+
}
3120+
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/* Can't send while already busy, either, unless enqueuing for later */
3122+
if (conn->asyncStatus!=PGASYNC_IDLE&&
3123+
conn->pipelineStatus==PQ_PIPELINE_OFF)
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{
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appendPQExpBufferStr(&conn->errorMessage,
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libpq_gettext("another command is already in progress\n"));
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return false;
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}
3129+
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if (pqPutMsgStart('H',conn)<0||
3131+
pqPutMsgEnd(conn)<0)
3132+
{
3133+
return0;
3134+
}
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return1;
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}
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/* ====== accessor funcs for PGresult ======== */
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‎src/interfaces/libpq/libpq-fe.h

Lines changed: 1 addition & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -470,6 +470,7 @@ extern intPQconsumeInput(PGconn *conn);
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externintPQenterPipelineMode(PGconn*conn);
471471
externintPQexitPipelineMode(PGconn*conn);
472472
externintPQpipelineSync(PGconn*conn);
473+
externintPQsendFlushRequest(PGconn*conn);
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/* LISTEN/NOTIFY support */
475476
externPGnotify*PQnotifies(PGconn*conn);

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