Hi!
Currently libpq sends B(ind), D(escribe), E(execute), S(ync) when
executing a prepared statement.
The response for that D message is a RowDescription, which doesn't
change during prepared
statement lifetime (with the attributes format being an exception, as
they aren't know before execution) .
In a presumably very common case of repeatedly executing the same
statement, this leads to
both client and server parsing/sending exactly the same RowDescritpion
data over and over again.
Instead, library user could acquire a statement result RowDescription
once (via PQdescribePrepared),
and reuse it in subsequent calls to PQexecPrepared and/or its async
friends. Doing it this way saves
a measurable amount of CPU for both client and server and saves a lot of
network traffic, for example:
when selecting a single row from a table with 30 columns, where each
column has 10-symbols name, and
every value in a row is a 10-symbols TEXT, i'm seeing an amount of bytes
sent to client decreased
by a factor of 2.8, and the CPU time client spends in userland decreased
by a factor of ~1.5.
The patch attached adds a family of functions
PQsendQueryPreparedPredescribed, PQgetResultPredescribed,
PQisBusyPredescribed,
which allow a user to do just that.
If the idea seems reasonable i'd be happy to extend these to
PQexecPrepared as well and cover it with tests.
P.S. This is my first time ever sending a patch via email, so please
don't hesitate to point at mistakes
i'm doing in the process.
diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt
index 850734ac96..989354ca06 100644
--- a/src/interfaces/libpq/exports.txt
+++ b/src/interfaces/libpq/exports.txt
@@ -191,3 +191,6 @@ PQclosePrepared 188
PQclosePortal 189
PQsendClosePrepared 190
PQsendClosePortal 191
+PQsendQueryPreparedPredescribed 192
+PQgetResultPredescribed 193
+PQisBusyPredescribed 194
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 04610ccf5e..a18bead9e6 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -72,8 +72,19 @@ static int PQsendQueryGuts(PGconn *conn,
const char *const *paramValues,
const int *paramLengths,
const int *paramFormats,
- int resultFormat);
-static void parseInput(PGconn *conn);
+ int resultFormat,
+ bool sendDescribe);
+static int PQsendQueryPreparedInternal(PGconn *conn,
+ const char *stmtName,
+ int nParams,
+ const char *const *paramValues,
+ const int *paramLengths,
+ const int *paramFormats,
+ int resultFormat,
+ bool sendDescribe);
+static int PQisBusyInternal(PGconn *conn, PGresult *description);
+static PGresult *PQgetResultInternal(PGconn *conn, PGresult *description);
+static void parseInput(PGconn *conn, PGresult *description);
static PGresult *getCopyResult(PGconn *conn, ExecStatusType copytype);
static bool PQexecStart(PGconn *conn);
static PGresult *PQexecFinish(PGconn *conn);
@@ -1528,7 +1539,8 @@ PQsendQueryParams(PGconn *conn,
paramValues,
paramLengths,
paramFormats,
- resultFormat);
+ resultFormat,
+ true /* send Describe */ );
}
/*
@@ -1643,6 +1655,26 @@ PQsendQueryPrepared(PGconn *conn,
const int *paramLengths,
const int *paramFormats,
int resultFormat)
+{
+ return PQsendQueryPreparedInternal(conn,
+ stmtName,
+ nParams,
+ paramValues,
+ paramLengths,
+ paramFormats,
+ resultFormat,
+ true /* send Describe */ );
+}
+
+int
+PQsendQueryPreparedInternal(PGconn *conn,
+ const char *stmtName,
+ int nParams,
+ const char *const *paramValues,
+ const int *paramLengths,
+ const int *paramFormats,
+ int resultFormat,
+ bool sendDescribe)
{
if (!PQsendQueryStart(conn, true))
return 0;
@@ -1668,7 +1700,50 @@ PQsendQueryPrepared(PGconn *conn,
paramValues,
paramLengths,
paramFormats,
- resultFormat);
+ resultFormat,
+ sendDescribe);
+}
+
+int
+PQsendQueryPreparedPredescribed(PGconn *conn,
+ const char *stmtName,
+ int nParams,
+ const char *const *paramValues,
+ const int *paramLengths,
+ const int *paramFormats,
+ int resultFormat,
+ PGresult *description)
+{
+ int i;
+ int nFields;
+ int send_result;
+
+ if (!description)
+ {
+ libpq_append_conn_error(conn, "query result description is a null pointer");
+ return 0;
+ }
+
+ send_result = PQsendQueryPreparedInternal(conn,
+ stmtName,
+ nParams,
+ paramValues,
+ paramLengths,
+ paramFormats,
+ resultFormat,
+ false /* send Describe */ );
+
+ /* We only need to adjust attributes format if send succeeded */
+ if (send_result && description->attDescs != NULL)
+ {
+ nFields = description->numAttributes;
+ for (i = 0; i < nFields; i++)
+ {
+ description->attDescs[i].format = resultFormat;
+ }
+ }
+
+ return send_result;
}
/*
@@ -1766,7 +1841,8 @@ PQsendQueryGuts(PGconn *conn,
const char *const *paramValues,
const int *paramLengths,
const int *paramFormats,
- int resultFormat)
+ int resultFormat,
+ bool sendDescribe)
{
int i;
PGcmdQueueEntry *entry;
@@ -1873,12 +1949,15 @@ PQsendQueryGuts(PGconn *conn,
if (pqPutMsgEnd(conn) < 0)
goto sendFailed;
- /* construct the Describe Portal message */
- if (pqPutMsgStart(PqMsg_Describe, conn) < 0 ||
- pqPutc('P', conn) < 0 ||
- pqPuts("", conn) < 0 ||
- pqPutMsgEnd(conn) < 0)
- goto sendFailed;
+ if (sendDescribe)
+ {
+ /* construct the Describe Portal message */
+ if (pqPutMsgStart(PqMsg_Describe, conn) < 0 ||
+ pqPutc('P', conn) < 0 ||
+ pqPuts("", conn) < 0 ||
+ pqPutMsgEnd(conn) < 0)
+ goto sendFailed;
+ }
/* construct the Execute message */
if (pqPutMsgStart(PqMsg_Execute, conn) < 0 ||
@@ -1990,9 +2069,9 @@ PQconsumeInput(PGconn *conn)
* Note that this function will NOT attempt to read more data from the backend.
*/
static void
-parseInput(PGconn *conn)
+parseInput(PGconn *conn, PGresult *description)
{
- pqParseInput3(conn);
+ pqParseInput3Predescribed(conn, description);
}
/*
@@ -2002,12 +2081,18 @@ parseInput(PGconn *conn)
int
PQisBusy(PGconn *conn)
+{
+ return PQisBusyInternal(conn, NULL);
+}
+
+static int
+PQisBusyInternal(PGconn *conn, PGresult *description)
{
if (!conn)
return false;
/* Parse any available data, if our state permits. */
- parseInput(conn);
+ parseInput(conn, description);
/*
* PQgetResult will return immediately in all states except BUSY. Also,
@@ -2020,6 +2105,12 @@ PQisBusy(PGconn *conn)
return conn->asyncStatus == PGASYNC_BUSY && conn->status != CONNECTION_BAD;
}
+int
+PQisBusyPredescribed(PGconn *conn, PGresult *description)
+{
+ return PQisBusyInternal(conn, description);
+}
+
/*
* PQgetResult
* Get the next PGresult produced by a query. Returns NULL if no
@@ -2033,6 +2124,12 @@ PQisBusy(PGconn *conn)
*/
PGresult *
PQgetResult(PGconn *conn)
+{
+ return PQgetResultInternal(conn, NULL);
+}
+
+static PGresult *
+PQgetResultInternal(PGconn *conn, PGresult *description)
{
PGresult *res;
@@ -2040,7 +2137,7 @@ PQgetResult(PGconn *conn)
return NULL;
/* Parse any available data, if our state permits. */
- parseInput(conn);
+ parseInput(conn, description);
/* If not ready to return something, block until we are. */
while (conn->asyncStatus == PGASYNC_BUSY)
@@ -2078,7 +2175,7 @@ PQgetResult(PGconn *conn)
}
/* Parse it. */
- parseInput(conn);
+ parseInput(conn, description);
/*
* If we had a write error, but nothing above obtained a query result
@@ -2182,6 +2279,12 @@ PQgetResult(PGconn *conn)
return res;
}
+PGresult *
+PQgetResultPredescribed(PGconn *conn, PGresult *description)
+{
+ return PQgetResultInternal(conn, description);
+}
+
/*
* getCopyResult
* Helper for PQgetResult: generate result for COPY-in-progress cases
@@ -2638,7 +2741,7 @@ PQnotifies(PGconn *conn)
return NULL;
/* Parse any available data to see if we can extract NOTIFY messages. */
- parseInput(conn);
+ parseInput(conn, NULL);
event = conn->notifyHead;
if (event)
@@ -2677,7 +2780,7 @@ PQputCopyData(PGconn *conn, const char *buffer, int nbytes)
* input data into the input buffer happens down inside pqSendSome, but
* it's not authorized to get rid of the data again.)
*/
- parseInput(conn);
+ parseInput(conn, NULL);
if (nbytes > 0)
{
diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 5613c56b14..8fa5853f84 100644
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -55,6 +55,7 @@ static void reportErrorPosition(PQExpBuffer msg, const char *query,
int loc, int encoding);
static int build_startup_packet(const PGconn *conn, char *packet,
const PQEnvironmentOption *options);
+static void pqParseInput3Internal(PGconn *conn, PGresult *description);
/*
@@ -62,8 +63,8 @@ static int build_startup_packet(const PGconn *conn, char *packet,
* until input is exhausted or a stopping state is reached.
* Note that this function will NOT attempt to read more data from the backend.
*/
-void
-pqParseInput3(PGconn *conn)
+static void
+pqParseInput3Internal(PGconn *conn, PGresult *description)
{
char id;
int msgLength;
@@ -402,11 +403,38 @@ pqParseInput3(PGconn *conn)
}
else
{
- /* Set up to report error at end of query */
- libpq_append_conn_error(conn, "server sent data (\"D\" message) without prior row description (\"T\" message)");
- pqSaveErrorResult(conn);
- /* Discard the unexpected message */
- conn->inCursor += msgLength;
+ if (!description)
+ {
+ /* Set up to report error at end of query */
+ libpq_append_conn_error(conn,
+ "server sent data (\"D\" message) without prior row description (\"T\" message)");
+ pqSaveErrorResult(conn);
+ /* Discard the unexpected message */
+ conn->inCursor += msgLength;
+ }
+ else
+ {
+ /*
+ * We didn't receive row description from the
+ * server, but we have externally provided
+ * description, use that.
+ */
+ if (conn->result == NULL)
+ {
+ conn->result = PQmakeEmptyPGresult(conn, PGRES_TUPLES_OK);
+ }
+ if (!conn->result)
+ {
+ libpq_append_conn_error(conn, "out of memory");
+ pqSaveErrorResult(conn);
+ }
+ else
+ {
+ PQsetResultAttrs(conn->result, description->numAttributes, description->attDescs);
+ if (getAnotherTuple(conn, msgLength))
+ return;
+ }
+ }
}
break;
case PqMsg_CopyInResponse:
@@ -478,6 +506,18 @@ pqParseInput3(PGconn *conn)
}
}
+void
+pqParseInput3(PGconn *conn)
+{
+ pqParseInput3Internal(conn, NULL);
+}
+
+void
+pqParseInput3Predescribed(PGconn *conn, PGresult *description)
+{
+ pqParseInput3Internal(conn, description);
+}
+
/*
* handleSyncLoss: clean up after loss of message-boundary sync
*
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 97762d56f5..573b68fea2 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -462,11 +462,21 @@ extern int PQsendQueryPrepared(PGconn *conn,
const int *paramLengths,
const int *paramFormats,
int resultFormat);
+extern int PQsendQueryPreparedPredescribed(PGconn *conn,
+ const char *stmtName,
+ int nParams,
+ const char *const *paramValues,
+ const int *paramLengths,
+ const int *paramFormats,
+ int resultFormat,
+ PGresult *description);
extern int PQsetSingleRowMode(PGconn *conn);
extern PGresult *PQgetResult(PGconn *conn);
+extern PGresult *PQgetResultPredescribed(PGconn *conn, PGresult *description);
/* Routines for managing an asynchronous query */
extern int PQisBusy(PGconn *conn);
+extern int PQisBusyPredescribed(PGconn *conn, PGresult *description);
extern int PQconsumeInput(PGconn *conn);
/* Routines for pipeline mode management */
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index c745facfec..df91c39fbe 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -706,6 +706,7 @@ extern int PQsendQueryContinue(PGconn *conn, const char *query);
extern char *pqBuildStartupPacket3(PGconn *conn, int *packetlen,
const PQEnvironmentOption *options);
extern void pqParseInput3(PGconn *conn);
+extern void pqParseInput3Predescribed(PGconn *conn, PGresult *description);
extern int pqGetErrorNotice3(PGconn *conn, bool isError);
extern void pqBuildErrorMessage3(PQExpBuffer msg, const PGresult *res,
PGVerbosity verbosity, PGContextVisibility show_context);
