Hi,
Here's a new version to improve the performance of FETCH_COUNT
and extend the cases when it can be used.
Patch 0001 adds a new mode in libpq to allow the app to retrieve
larger chunks of results than the single row of the row-by-row mode.
The maximum number of rows per PGresult is set by the user.
Patch 0002 uses that mode in psql and gets rid of the cursor
implementation as suggested upthread.
The performance numbers look good.
For a query retrieving 50M rows of about 200 bytes:
select repeat('abc', 200) from generate_series(1,5000000)
/usr/bin/time -v psql -At -c $query reports these metrics
(medians of 5 runs):
version | fetch_count | clock_time | user_time | sys_time | max_rss_size
(kB)
-----------+-------------+------------+-----------+----------+-------------------
16-stable | 0 | 6.58 | 3.98 | 2.09 |
3446276
16-stable | 100 | 9.25 | 4.10 | 1.90 |
8768
16-stable | 1000 | 11.13 | 5.17 | 1.66 |
8904
17-patch | 0 | 6.5 | 3.94 | 2.09 |
3442696
17-patch | 100 | 5 | 3.56 | 0.93 |
4096
17-patch | 1000 | 6.48 | 4.00 | 1.55 |
4344
Interestingly, retrieving by chunks of 100 rows appears to be a bit faster
than the default one big chunk. It means that independently
of using less memory, FETCH_COUNT implemented that way
would be a performance enhancement compared to both
not using it and using it in v16 with the cursor implementation.
Best regards,
--
Daniel Vérité
https://postgresql.verite.pro/
Twitter: @DanielVerite
From 766bbe84def2db494f646caeaf29eefeba893c1a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20V=C3=A9rit=C3=A9?= <dan...@manitou-mail.org>
Date: Mon, 20 Nov 2023 17:24:55 +0100
Subject: [PATCH v4 1/2] Implement retrieval of results in chunks with libpq.
This mode is similar to the single-row mode except that chunks
of results contain up to N rows instead of a single row.
It is meant to reduce the overhead of the row-by-row allocations
for large result sets.
The mode is selected with PQsetChunkedRowsMode(int maxRows) and results
have the new status code PGRES_TUPLES_CHUNK.
---
doc/src/sgml/libpq.sgml | 96 +++++++++++++++++++------
src/bin/pg_amcheck/pg_amcheck.c | 1 +
src/interfaces/libpq/exports.txt | 1 +
src/interfaces/libpq/fe-exec.c | 118 +++++++++++++++++++++++++------
src/interfaces/libpq/libpq-fe.h | 4 +-
src/interfaces/libpq/libpq-int.h | 7 +-
6 files changed, 183 insertions(+), 44 deletions(-)
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
index ed88ac001a..8007bf67d8 100644
--- a/doc/src/sgml/libpq.sgml
+++ b/doc/src/sgml/libpq.sgml
@@ -3537,7 +3537,20 @@ ExecStatusType PQresultStatus(const PGresult *res);
The <structname>PGresult</structname> contains a single result
tuple
from the current command. This status occurs only when
single-row mode has been selected for the query
- (see <xref linkend="libpq-single-row-mode"/>).
+ (see <xref linkend="libpq-chunked-results-modes"/>).
+ </para>
+ </listitem>
+ </varlistentry>
+
+ <varlistentry id="libpq-pgres-tuples-chunk">
+ <term><literal>PGRES_TUPLES_CHUNK</literal></term>
+ <listitem>
+ <para>
+ The <structname>PGresult</structname> contains several tuples
+ from the current command. The count of tuples cannot exceed
+ the maximum passed to <xref linkend="libpq-PQsetChunkedRowsMode"/>.
+ This status occurs only when the chunked mode has been selected
+ for the query (see <xref linkend="libpq-chunked-results-modes"/>).
</para>
</listitem>
</varlistentry>
@@ -5187,8 +5200,8 @@ PGresult *PQgetResult(PGconn *conn);
<para>
Another frequently-desired feature that can be obtained with
<xref linkend="libpq-PQsendQuery"/> and <xref linkend="libpq-PQgetResult"/>
- is retrieving large query results a row at a time. This is discussed
- in <xref linkend="libpq-single-row-mode"/>.
+ is retrieving large query results a limited number of rows at a time. This
is discussed
+ in <xref linkend="libpq-chunked-results-modes"/>.
</para>
<para>
@@ -5551,12 +5564,13 @@ int PQflush(PGconn *conn);
</para>
<para>
- To enter single-row mode, call <function>PQsetSingleRowMode</function>
- before retrieving results with <function>PQgetResult</function>.
- This mode selection is effective only for the query currently
- being processed. For more information on the use of
- <function>PQsetSingleRowMode</function>,
- refer to <xref linkend="libpq-single-row-mode"/>.
+ To enter single-row or chunked modes, call
+ respectively <function>PQsetSingleRowMode</function>
+ or <function>PQsetChunkedRowsMode</function> before retrieving results
+ with <function>PQgetResult</function>. This mode selection is effective
+ only for the query currently being processed. For more information on the
+ use of these functions refer
+ to <xref linkend="libpq-chunked-results-modes" />.
</para>
<para>
@@ -5895,10 +5909,10 @@ UPDATE mytable SET x = x + 1 WHERE id = 42;
</sect2>
</sect1>
- <sect1 id="libpq-single-row-mode">
- <title>Retrieving Query Results Row-by-Row</title>
+ <sect1 id="libpq-chunked-results-modes">
+ <title>Retrieving Query Results by chunks</title>
- <indexterm zone="libpq-single-row-mode">
+ <indexterm zone="libpq-chunked-results-modes">
<primary>libpq</primary>
<secondary>single-row mode</secondary>
</indexterm>
@@ -5909,13 +5923,15 @@ UPDATE mytable SET x = x + 1 WHERE id = 42;
<structname>PGresult</structname>. This can be unworkable for commands
that return a large number of rows. For such cases, applications can use
<xref linkend="libpq-PQsendQuery"/> and <xref linkend="libpq-PQgetResult"/>
in
- <firstterm>single-row mode</firstterm>. In this mode, the result row(s) are
- returned to the application one at a time, as they are received from the
- server.
+ <firstterm>single-row mode</firstterm> or <firstterm>chunked
mode</firstterm>.
+ In these modes, the result row(s) are returned to the application one at a
+ time for the single-row mode and by chunks for the chunked mode, as they
+ are received from the server.
</para>
<para>
- To enter single-row mode, call <xref linkend="libpq-PQsetSingleRowMode"/>
+ To enter these modes, call <xref linkend="libpq-PQsetSingleRowMode"/>
+ or <xref linkend="libpq-PQsetChunkedRowsMode"/>
immediately after a successful call of <xref linkend="libpq-PQsendQuery"/>
(or a sibling function). This mode selection is effective only for the
currently executing query. Then call <xref linkend="libpq-PQgetResult"/>
@@ -5923,7 +5939,8 @@ UPDATE mytable SET x = x + 1 WHERE id = 42;
linkend="libpq-async"/>. If the query returns any rows, they are returned
as individual <structname>PGresult</structname> objects, which look like
normal query results except for having status code
- <literal>PGRES_SINGLE_TUPLE</literal> instead of
+ <literal>PGRES_SINGLE_TUPLE</literal> for the single-row mode and
+ <literal>PGRES_TUPLES_CHUNK</literal> for the chunked mode, instead of
<literal>PGRES_TUPLES_OK</literal>. After the last row, or immediately if
the query returns zero rows, a zero-row object with status
<literal>PGRES_TUPLES_OK</literal> is returned; this is the signal that no
@@ -5936,9 +5953,9 @@ UPDATE mytable SET x = x + 1 WHERE id = 42;
</para>
<para>
- When using pipeline mode, single-row mode needs to be activated for each
- query in the pipeline before retrieving results for that query
- with <function>PQgetResult</function>.
+ When using pipeline mode, the single-row or chunked mode need to be
+ activated for each query in the pipeline before retrieving results for that
+ query with <function>PQgetResult</function>.
See <xref linkend="libpq-pipeline-mode"/> for more information.
</para>
@@ -5972,14 +5989,49 @@ int PQsetSingleRowMode(PGconn *conn);
</variablelist>
</para>
+ <para>
+ <variablelist>
+ <varlistentry id="libpq-PQsetChunkedRowsMode">
+ <term><function>PQsetChunkedRowsMode</function>
+ <indexterm><primary>PQsetChunkedRowsMode</primary></indexterm></term>
+ <listitem>
+ <para>
+ Select the mode retrieving results in chunks for the
currently-executing query.
+
+<synopsis>
+ int PQsetChunkedRowsMode(PGconn *conn,
+ int maxRows);
+</synopsis>
+ </para>
+
+ <para>
+ This function is similar to <xref linkend="libpq-PQsetSingleRowMode"/>,
+ except that it can retrieve a user-specified number of rows
+ per call to <xref linkend="libpq-PQgetResult"/>, instead of a single
row.
+ This function can only be called immediately after
+ <xref linkend="libpq-PQsendQuery"/> or one of its sibling functions,
+ before any other operation on the connection such as
+ <xref linkend="libpq-PQconsumeInput"/> or
+ <xref linkend="libpq-PQgetResult"/>. If called at the correct time,
+ the function activates the chunked mode for the current query and
+ returns 1. Otherwise the mode stays unchanged and the function
+ returns 0. In any case, the mode reverts to normal after
+ completion of the current query.
+ </para>
+ </listitem>
+ </varlistentry>
+ </variablelist>
+ </para>
+
<caution>
<para>
While processing a query, the server may return some rows and then
encounter an error, causing the query to be aborted. Ordinarily,
<application>libpq</application> discards any such rows and reports only
the
- error. But in single-row mode, those rows will have already been
+ error. But in single-row or chunked modes, those rows will have already
been
returned to the application. Hence, the application will see some
- <literal>PGRES_SINGLE_TUPLE</literal> <structname>PGresult</structname>
+ <literal>PGRES_SINGLE_TUPLE</literal> or
<literal>PGRES_TUPLES_CHUNK</literal>
+ <structname>PGresult</structname>
objects followed by a <literal>PGRES_FATAL_ERROR</literal> object. For
proper transactional behavior, the application must be designed to
discard or undo whatever has been done with the previously-processed
diff --git a/src/bin/pg_amcheck/pg_amcheck.c b/src/bin/pg_amcheck/pg_amcheck.c
index a6b3b56457..9c8a0916c7 100644
--- a/src/bin/pg_amcheck/pg_amcheck.c
+++ b/src/bin/pg_amcheck/pg_amcheck.c
@@ -989,6 +989,7 @@ should_processing_continue(PGresult *res)
case PGRES_COPY_IN:
case PGRES_COPY_BOTH:
case PGRES_SINGLE_TUPLE:
+ case PGRES_TUPLES_CHUNK:
case PGRES_PIPELINE_SYNC:
case PGRES_PIPELINE_ABORTED:
return false;
diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt
index 850734ac96..ae7c84247b 100644
--- a/src/interfaces/libpq/exports.txt
+++ b/src/interfaces/libpq/exports.txt
@@ -191,3 +191,4 @@ PQclosePrepared 188
PQclosePortal 189
PQsendClosePrepared 190
PQsendClosePortal 191
+PQsetChunkedRowsMode 192
diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 04610ccf5e..2e96d1b538 100644
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -41,7 +41,8 @@ char *const pgresStatus[] = {
"PGRES_COPY_BOTH",
"PGRES_SINGLE_TUPLE",
"PGRES_PIPELINE_SYNC",
- "PGRES_PIPELINE_ABORTED"
+ "PGRES_PIPELINE_ABORTED",
+ "PGRES_TUPLES_CHUNK"
};
/* We return this if we're unable to make a PGresult at all */
@@ -82,7 +83,7 @@ static int PQsendTypedCommand(PGconn *conn, char command,
char type,
static int check_field_number(const PGresult *res, int field_num);
static void pqPipelineProcessQueue(PGconn *conn);
static int pqPipelineFlush(PGconn *conn);
-
+static bool canChangeRowMode(PGconn *conn);
/* ----------------
* Space management for PGresult.
@@ -199,6 +200,7 @@ PQmakeEmptyPGresult(PGconn *conn, ExecStatusType status)
case PGRES_COPY_IN:
case PGRES_COPY_BOTH:
case PGRES_SINGLE_TUPLE:
+ case PGRES_TUPLES_CHUNK:
/* non-error cases */
break;
default:
@@ -910,8 +912,9 @@ pqPrepareAsyncResult(PGconn *conn)
/*
* Replace conn->result with next_result, if any. In the normal case
* there isn't a next result and we're just dropping ownership of the
- * current result. In single-row mode this restores the situation to
what
- * it was before we created the current single-row result.
+ * current result. In single-row and chunked modes this restores the
+ * situation to what it was before we created the current single-row or
+ * chunk-of-rows result.
*/
conn->result = conn->next_result;
conn->error_result = false; /* next_result is never an error */
@@ -1197,10 +1200,11 @@ pqSaveParameterStatus(PGconn *conn, const char *name,
const char *value)
* (Such a string should already be translated via libpq_gettext().)
* If it is left NULL, the error is presumed to be "out of memory".
*
- * In single-row mode, we create a new result holding just the current row,
- * stashing the previous result in conn->next_result so that it becomes
- * active again after pqPrepareAsyncResult(). This allows the result metadata
- * (column descriptions) to be carried forward to each result row.
+ * In single-row or chunked mode, we create a new result holding just the
+ * current set of rows, stashing the previous result in conn->next_result so
+ * that it becomes active again after pqPrepareAsyncResult(). This allows the
+ * result metadata (column descriptions) to be carried forward to each result
+ * row.
*/
int
pqRowProcessor(PGconn *conn, const char **errmsgp)
@@ -1225,6 +1229,28 @@ pqRowProcessor(PGconn *conn, const char **errmsgp)
if (!res)
return 0;
}
+ else if (conn->rowsChunkSize > 0)
+ {
+ /*
+ * In chunked mode, make a new PGresult that will hold N rows;
the
+ * original conn->result is left unchanged, as in the
single-row mode.
+ */
+ if (!conn->chunk_result)
+ {
+ /* Allocate and initialize the result to hold a chunk
of rows */
+ res = PQcopyResult(res,
+ PG_COPYRES_ATTRS |
PG_COPYRES_EVENTS |
+
PG_COPYRES_NOTICEHOOKS);
+ if (!res)
+ return 0;
+ /* Change result status to special chunk-of-rows value
*/
+ res->resultStatus = PGRES_TUPLES_CHUNK;
+ /* Keep this result to reuse for the next rows of the
chunk */
+ conn->chunk_result = res;
+ }
+ else
+ res = conn->chunk_result; /* Use the current
chunk */
+ }
/*
* Basically we just allocate space in the PGresult for each field and
@@ -1287,6 +1313,21 @@ pqRowProcessor(PGconn *conn, const char **errmsgp)
conn->asyncStatus = PGASYNC_READY_MORE;
}
+ /*
+ * In chunked mode, if the count has reached the requested limit, make
the
+ * rows of the current chunk available immediately.
+ */
+ else if (conn->rowsChunkSize > 0 && res->ntups >= conn->rowsChunkSize)
+ {
+ /* Stash old result for re-use later */
+ conn->next_result = conn->result;
+ conn->result = res;
+ /* Do not reuse that chunk of results */
+ conn->chunk_result = NULL;
+ /* And mark the result ready to return */
+ conn->asyncStatus = PGASYNC_READY_MORE;
+ }
+
return 1;
fail:
@@ -1742,8 +1783,9 @@ PQsendQueryStart(PGconn *conn, bool newQuery)
*/
pqClearAsyncResult(conn);
- /* reset single-row processing mode */
+ /* reset row-by-row and chunked processing modes */
conn->singleRowMode = false;
+ conn->rowsChunkSize = 0;
}
/* ready to send command message */
@@ -1927,25 +1969,51 @@ sendFailed:
*/
int
PQsetSingleRowMode(PGconn *conn)
+{
+ if (canChangeRowMode(conn))
+ {
+ conn->singleRowMode = true;
+ return 1;
+ }
+ else
+ return 0;
+}
+
+/*
+ * Select chunked results processing mode
+ */
+int
+PQsetChunkedRowsMode(PGconn *conn, int chunkSize)
+{
+ if (chunkSize >= 0 && canChangeRowMode(conn))
+ {
+ conn->rowsChunkSize = chunkSize;
+ return 1;
+ }
+ else
+ return 0;
+}
+
+static
+bool
+canChangeRowMode(PGconn *conn)
{
/*
- * Only allow setting the flag when we have launched a query and not yet
- * received any results.
+ * Only allow setting the row-by-row or by-chunks modes when we have
+ * launched a query and not yet received any results.
*/
if (!conn)
- return 0;
+ return false;
if (conn->asyncStatus != PGASYNC_BUSY)
- return 0;
+ return false;
if (!conn->cmd_queue_head ||
(conn->cmd_queue_head->queryclass != PGQUERY_SIMPLE &&
conn->cmd_queue_head->queryclass != PGQUERY_EXTENDED))
- return 0;
+ return false;
if (pgHavePendingResult(conn))
- return 0;
+ return false;
- /* OK, set flag */
- conn->singleRowMode = true;
- return 1;
+ return true;
}
/*
@@ -2113,6 +2181,16 @@ PQgetResult(PGconn *conn)
case PGASYNC_READY:
+ /*
+ * If there is a pending chunk of results, return it
+ */
+ if (conn->chunk_result != NULL)
+ {
+ res = conn->chunk_result;
+ conn->chunk_result = NULL;
+ break;
+ }
+
/*
* For any query type other than simple query protocol,
we advance
* the command queue here. This is because for simple
query
@@ -3151,10 +3229,10 @@ pqPipelineProcessQueue(PGconn *conn)
}
/*
- * Reset single-row processing mode. (Client has to set it up for each
+ * Reset processing mode in chunks. (Client has to set it up for each
* query, if desired.)
*/
- conn->singleRowMode = false;
+ conn->rowsChunkSize = 0;
/*
* If there are no further commands to process in the queue, get us in
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 97762d56f5..002ed772c8 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -109,8 +109,9 @@ typedef enum
PGRES_COPY_BOTH, /* Copy In/Out data transfer in
progress */
PGRES_SINGLE_TUPLE, /* single tuple from larger
resultset */
PGRES_PIPELINE_SYNC, /* pipeline synchronization point */
- PGRES_PIPELINE_ABORTED /* Command didn't run because of an
abort
+ PGRES_PIPELINE_ABORTED, /* Command didn't run because of an
abort
* earlier in a
pipeline */
+ PGRES_TUPLES_CHUNK /* set of tuples from larger
resultset */
} ExecStatusType;
typedef enum
@@ -463,6 +464,7 @@ extern int PQsendQueryPrepared(PGconn *conn,
const int
*paramFormats,
int
resultFormat);
extern int PQsetSingleRowMode(PGconn *conn);
+extern int PQsetChunkedRowsMode(PGconn *conn, int chunkSize);
extern PGresult *PQgetResult(PGconn *conn);
/* Routines for managing an asynchronous query */
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index c745facfec..7786bd2435 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -431,6 +431,8 @@ struct pg_conn
* sending
semantics */
PGpipelineStatus pipelineStatus; /* status of pipeline mode */
bool singleRowMode; /* return current query result
row-by-row? */
+ int rowsChunkSize; /* non-zero to return query
results by chunks
+ * not
exceeding that number of rows */
char copy_is_binary; /* 1 = copy binary, 0 = copy text */
int copy_already_done; /* # bytes already
returned in COPY OUT */
PGnotify *notifyHead; /* oldest unreported Notify msg */
@@ -536,7 +538,10 @@ struct pg_conn
*/
PGresult *result; /* result being constructed */
bool error_result; /* do we need to make an ERROR result?
*/
- PGresult *next_result; /* next result (used in single-row
mode) */
+ PGresult *next_result; /* next result (used in single-row and
+ * by-chunks
modes) */
+ PGresult *chunk_result; /* current chunk of results (limited to
+ *
rowsChunkSize) */
/* Assorted state for SASL, SSL, GSS, etc */
const pg_fe_sasl_mech *sasl;
--
2.34.1
From a5555f339d88ad2a77e567cfd249cb948871b796 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20V=C3=A9rit=C3=A9?= <dan...@manitou-mail.org>
Date: Mon, 20 Nov 2023 18:42:41 +0100
Subject: [PATCH v4 2/2] Reimplement FETCH_COUNT with the chunked mode in libpq
instead of cursors.
Cursors were used only when the command starts with the keyword "SELECT",
excluding queries that start with "WITH" or "UPDATE" or "INSERT" that
may also return large result sets.
Also, cursors imply more commands sent to the server (begin/declare cursor
/repeated fetch/close cursor/commit), whereas in chunked mode, only the actual
user query is sent, resulting in less round-trips.
This also fixes the bug that combined queries (query1 \; query2;) were
not correctly handled with FETCH_COUNT set, due to cursors not supporting
multiple queries.
---
src/bin/psql/common.c | 545 ++++++++++-------------------
src/bin/psql/t/001_basic.pl | 6 +-
src/test/regress/expected/psql.out | 9 +-
src/test/regress/sql/psql.sql | 4 +-
4 files changed, 196 insertions(+), 368 deletions(-)
diff --git a/src/bin/psql/common.c b/src/bin/psql/common.c
index daabf6f12b..adb915e5c2 100644
--- a/src/bin/psql/common.c
+++ b/src/bin/psql/common.c
@@ -31,7 +31,6 @@
#include "settings.h"
static bool DescribeQuery(const char *query, double *elapsed_msec);
-static bool ExecQueryUsingCursor(const char *query, double *elapsed_msec);
static int ExecQueryAndProcessResults(const char *query,
double *elapsed_msec,
bool
*svpt_gone_p,
@@ -40,8 +39,6 @@ static int ExecQueryAndProcessResults(const char *query,
const printQueryOpt *opt,
FILE
*printQueryFout);
static bool command_no_begin(const char *query);
-static bool is_select_command(const char *query);
-
/*
* openQueryOutputFile --- attempt to open a query output file
@@ -373,6 +370,7 @@ AcceptResult(const PGresult *result, bool show_error)
{
case PGRES_COMMAND_OK:
case PGRES_TUPLES_OK:
+ case PGRES_TUPLES_CHUNK:
case PGRES_EMPTY_QUERY:
case PGRES_COPY_IN:
case PGRES_COPY_OUT:
@@ -1131,16 +1129,10 @@ SendQuery(const char *query)
/* Describe query's result columns, without executing it */
OK = DescribeQuery(query, &elapsed_msec);
}
- else if (pset.fetch_count <= 0 || pset.gexec_flag ||
- pset.crosstab_flag || !is_select_command(query))
- {
- /* Default fetch-it-all-and-print mode */
- OK = (ExecQueryAndProcessResults(query, &elapsed_msec,
&svpt_gone, false, 0, NULL, NULL) > 0);
- }
else
{
- /* Fetch-in-segments mode */
- OK = ExecQueryUsingCursor(query, &elapsed_msec);
+ /* Default fetch-and-print mode */
+ OK = (ExecQueryAndProcessResults(query, &elapsed_msec,
&svpt_gone, false, 0, NULL, NULL) > 0);
}
if (!OK && pset.echo == PSQL_ECHO_ERRORS)
@@ -1392,6 +1384,47 @@ DescribeQuery(const char *query, double *elapsed_msec)
return OK;
}
+/*
+ * Check if an output stream for \g needs to be opened, and if
+ * yes, open it.
+ * Return false if an error occurred, true otherwise.
+ */
+static bool
+SetupGOutput(PGresult *result, FILE **gfile_fout, bool *is_pipe)
+{
+ ExecStatusType status = PQresultStatus(result);
+ if (pset.gfname != NULL && /* there is a \g file
or program */
+ *gfile_fout == NULL && /* and it's not already opened
*/
+ (status == PGRES_TUPLES_OK ||
+ status == PGRES_TUPLES_CHUNK ||
+ status == PGRES_COPY_OUT))
+ {
+ if (openQueryOutputFile(pset.gfname, gfile_fout, is_pipe))
+ {
+ if (is_pipe)
+ disable_sigpipe_trap();
+ }
+ else
+ return false;
+ }
+ return true;
+}
+
+static void
+CloseGOutput(FILE *gfile_fout, bool is_pipe)
+{
+ /* close \g file if we opened it */
+ if (gfile_fout)
+ {
+ if (is_pipe)
+ {
+ SetShellResultVariables(pclose(gfile_fout));
+ restore_sigpipe_trap();
+ }
+ else
+ fclose(gfile_fout);
+ }
+}
/*
* ExecQueryAndProcessResults: utility function for use by SendQuery()
@@ -1424,10 +1457,16 @@ ExecQueryAndProcessResults(const char *query,
bool return_early = false;
instr_time before,
after;
+ int fetch_count = pset.fetch_count;
PGresult *result;
+
FILE *gfile_fout = NULL;
bool gfile_is_pipe = false;
+ int64 total_tuples = 0;
+ int flush_error = 0;
+ bool is_pager = false;
+
if (timing)
INSTR_TIME_SET_CURRENT(before);
else
@@ -1450,6 +1489,29 @@ ExecQueryAndProcessResults(const char *query,
return -1;
}
+ /*
+ * If FETCH_COUNT is set and the context allows it, use the single row
+ * mode to fetch results and have no more than FETCH_COUNT rows in
+ * memory.
+ */
+ if (fetch_count > 0 && !pset.crosstab_flag && !pset.gexec_flag &&
!is_watch
+ && !pset.gset_prefix && pset.show_all_results)
+ {
+ /*
+ * The row-by-chunks fetch is not enabled when SHOW_ALL_RESULTS
is false,
+ * since we would need to accumulate all rows before knowing
+ * whether they need to be discarded or displayed, which
contradicts
+ * FETCH_COUNT.
+ */
+ if (!PQsetChunkedRowsMode(pset.db, fetch_count))
+ {
+ pg_log_warning("fetching results in chunks mode is
unavailable");
+ fetch_count = 0;
+ }
+ }
+ else
+ fetch_count = 0; /* fetch one resultset per
query */
+
/*
* If SIGINT is sent while the query is processing, the interrupt will
be
* consumed. The user's intention, though, is to cancel the entire
watch
@@ -1473,6 +1535,8 @@ ExecQueryAndProcessResults(const char *query,
ExecStatusType result_status;
PGresult *next_result;
bool last;
+ /* whether the output starts before results are fully fetched */
+ bool partial_display = false;
if (!AcceptResult(result, false))
{
@@ -1568,20 +1632,9 @@ ExecQueryAndProcessResults(const char *query,
}
else if (pset.gfname)
{
- /* send to \g file, which we may have
opened already */
- if (gfile_fout == NULL)
- {
- if
(openQueryOutputFile(pset.gfname,
-
&gfile_fout, &gfile_is_pipe))
- {
- if (gfile_is_pipe)
-
disable_sigpipe_trap();
- copy_stream =
gfile_fout;
- }
- else
- success = false;
- }
- else
+ /* COPY followed by \g filename or \g
|program */
+ success = SetupGOutput(result,
&gfile_fout, &gfile_is_pipe);
+ if (success)
copy_stream = gfile_fout;
}
else
@@ -1599,6 +1652,90 @@ ExecQueryAndProcessResults(const char *query,
success &= HandleCopyResult(&result, copy_stream);
}
+ if (fetch_count > 0 && result_status == PGRES_TUPLES_CHUNK)
+ {
+ FILE *tuples_fout = printQueryFout ?
printQueryFout : stdout;
+ printQueryOpt my_popt = pset.popt;
+
+ total_tuples = 0;
+ partial_display = true;
+
+ success = SetupGOutput(result, &gfile_fout,
&gfile_is_pipe);
+ if (gfile_fout)
+ tuples_fout = gfile_fout;
+
+ /* initialize print options for partial table output */
+ my_popt.topt.start_table = true;
+ my_popt.topt.stop_table = false;
+ my_popt.topt.prior_records = 0;
+
+ while (success)
+ {
+ /* pager: open at most once per resultset */
+ if (tuples_fout == stdout && !is_pager)
+ {
+ tuples_fout = PageOutput(INT_MAX,
&(my_popt.topt));
+ is_pager = true;
+ }
+ /* display the current chunk of results unless
the output stream is not working */
+ if (!flush_error)
+ {
+ printQuery(result, &my_popt,
tuples_fout, is_pager, pset.logfile);
+ flush_error = fflush(tuples_fout);
+ }
+
+ /* after the first result set, disallow header
decoration */
+ my_popt.topt.start_table = false;
+ my_popt.topt.prior_records += PQntuples(result);
+ total_tuples += PQntuples(result);
+
+ ClearOrSaveResult(result);
+
+ result = PQgetResult(pset.db);
+ if (result == NULL)
+ {
+ /*
+ * Error. We expect a PGRES_TUPLES_OK
result with
+ * zero tuple in it to finish the fetch
sequence.
+ */
+ success = false;
+ if (is_pager)
+ ClosePager(tuples_fout);
+ break;
+ }
+ else if (PQresultStatus(result) ==
PGRES_TUPLES_OK)
+ {
+ /*
+ * The last row has been read. Display
the footer.
+ */
+ my_popt.topt.stop_table = true;
+ printQuery(result, &my_popt,
tuples_fout, is_pager, pset.logfile);
+ total_tuples += PQntuples(result);
+
+ if (is_pager)
+ ClosePager(tuples_fout);
+ ClearOrSaveResult(result);
+ result = NULL;
+ break;
+ }
+ else if (PQresultStatus(result) !=
PGRES_TUPLES_CHUNK)
+ {
+ /*
+ * Error. We expect either
PGRES_TUPLES_CHUNK or
+ * PGRES_TUPLES_OK.
+ */
+ if (is_pager)
+ ClosePager(tuples_fout);
+ success = false;
+ AcceptResult(result, true); /* display
error whenever appropriate */
+ SetResultVariables(result, success);
+ break;
+ }
+ }
+ }
+ else
+ partial_display = false;
+
/*
* Check PQgetResult() again. In the typical case of a
single-command
* string, it will return NULL. Otherwise, we'll have other
results
@@ -1627,7 +1764,7 @@ ExecQueryAndProcessResults(const char *query,
}
/* this may or may not print something depending on settings */
- if (result != NULL)
+ if (result != NULL && !partial_display)
{
/*
* If results need to be printed into the file
specified by \g,
@@ -1636,32 +1773,33 @@ ExecQueryAndProcessResults(const char *query,
* tuple output, but it's still used for status output.
*/
FILE *tuples_fout = printQueryFout;
- bool do_print = true;
-
- if (PQresultStatus(result) == PGRES_TUPLES_OK &&
- pset.gfname)
- {
- if (gfile_fout == NULL)
- {
- if (openQueryOutputFile(pset.gfname,
-
&gfile_fout, &gfile_is_pipe))
- {
- if (gfile_is_pipe)
- disable_sigpipe_trap();
- }
- else
- success = do_print = false;
- }
+ success = SetupGOutput(result, &gfile_fout,
&gfile_is_pipe);
+ if (gfile_fout)
tuples_fout = gfile_fout;
- }
- if (do_print)
+ if (success)
success &= PrintQueryResult(result, last, opt,
tuples_fout, printQueryFout);
}
/* set variables from last result */
if (!is_watch && last)
- SetResultVariables(result, success);
+ {
+ if (!partial_display)
+ SetResultVariables(result, success);
+ else if (success)
+ {
+ /*
+ * fake SetResultVariables(). If an error
occurred when
+ * retrieving chunks, these variables have been
set already.
+ */
+ char buf[32];
+
+ SetVariable(pset.vars, "ERROR", "false");
+ SetVariable(pset.vars, "SQLSTATE", "00000");
+ snprintf(buf, sizeof(buf), INT64_FORMAT,
total_tuples);
+ SetVariable(pset.vars, "ROW_COUNT", buf);
+ }
+ }
ClearOrSaveResult(result);
result = next_result;
@@ -1673,17 +1811,7 @@ ExecQueryAndProcessResults(const char *query,
}
}
- /* close \g file if we opened it */
- if (gfile_fout)
- {
- if (gfile_is_pipe)
- {
- SetShellResultVariables(pclose(gfile_fout));
- restore_sigpipe_trap();
- }
- else
- fclose(gfile_fout);
- }
+ CloseGOutput(gfile_fout, gfile_is_pipe);
/* may need this to recover from conn loss during COPY */
if (!CheckConnection())
@@ -1696,274 +1824,6 @@ ExecQueryAndProcessResults(const char *query,
}
-/*
- * ExecQueryUsingCursor: run a SELECT-like query using a cursor
- *
- * This feature allows result sets larger than RAM to be dealt with.
- *
- * Returns true if the query executed successfully, false otherwise.
- *
- * If pset.timing is on, total query time (exclusive of result-printing) is
- * stored into *elapsed_msec.
- */
-static bool
-ExecQueryUsingCursor(const char *query, double *elapsed_msec)
-{
- bool OK = true;
- PGresult *result;
- PQExpBufferData buf;
- printQueryOpt my_popt = pset.popt;
- bool timing = pset.timing;
- FILE *fout;
- bool is_pipe;
- bool is_pager = false;
- bool started_txn = false;
- int64 total_tuples = 0;
- int ntuples;
- int fetch_count;
- char fetch_cmd[64];
- instr_time before,
- after;
- int flush_error;
-
- *elapsed_msec = 0;
-
- /* initialize print options for partial table output */
- my_popt.topt.start_table = true;
- my_popt.topt.stop_table = false;
- my_popt.topt.prior_records = 0;
-
- if (timing)
- INSTR_TIME_SET_CURRENT(before);
- else
- INSTR_TIME_SET_ZERO(before);
-
- /* if we're not in a transaction, start one */
- if (PQtransactionStatus(pset.db) == PQTRANS_IDLE)
- {
- result = PQexec(pset.db, "BEGIN");
- OK = AcceptResult(result, true) &&
- (PQresultStatus(result) == PGRES_COMMAND_OK);
- ClearOrSaveResult(result);
- if (!OK)
- return false;
- started_txn = true;
- }
-
- /* Send DECLARE CURSOR */
- initPQExpBuffer(&buf);
- appendPQExpBuffer(&buf, "DECLARE _psql_cursor NO SCROLL CURSOR FOR\n%s",
- query);
-
- result = PQexec(pset.db, buf.data);
- OK = AcceptResult(result, true) &&
- (PQresultStatus(result) == PGRES_COMMAND_OK);
- if (!OK)
- SetResultVariables(result, OK);
- ClearOrSaveResult(result);
- termPQExpBuffer(&buf);
- if (!OK)
- goto cleanup;
-
- if (timing)
- {
- INSTR_TIME_SET_CURRENT(after);
- INSTR_TIME_SUBTRACT(after, before);
- *elapsed_msec += INSTR_TIME_GET_MILLISEC(after);
- }
-
- /*
- * In \gset mode, we force the fetch count to be 2, so that we will
throw
- * the appropriate error if the query returns more than one row.
- */
- if (pset.gset_prefix)
- fetch_count = 2;
- else
- fetch_count = pset.fetch_count;
-
- snprintf(fetch_cmd, sizeof(fetch_cmd),
- "FETCH FORWARD %d FROM _psql_cursor",
- fetch_count);
-
- /* prepare to write output to \g argument, if any */
- if (pset.gfname)
- {
- if (!openQueryOutputFile(pset.gfname, &fout, &is_pipe))
- {
- OK = false;
- goto cleanup;
- }
- if (is_pipe)
- disable_sigpipe_trap();
- }
- else
- {
- fout = pset.queryFout;
- is_pipe = false; /* doesn't matter */
- }
-
- /* clear any pre-existing error indication on the output stream */
- clearerr(fout);
-
- for (;;)
- {
- if (timing)
- INSTR_TIME_SET_CURRENT(before);
-
- /* get fetch_count tuples at a time */
- result = PQexec(pset.db, fetch_cmd);
-
- if (timing)
- {
- INSTR_TIME_SET_CURRENT(after);
- INSTR_TIME_SUBTRACT(after, before);
- *elapsed_msec += INSTR_TIME_GET_MILLISEC(after);
- }
-
- if (PQresultStatus(result) != PGRES_TUPLES_OK)
- {
- /* shut down pager before printing error message */
- if (is_pager)
- {
- ClosePager(fout);
- is_pager = false;
- }
-
- OK = AcceptResult(result, true);
- Assert(!OK);
- SetResultVariables(result, OK);
- ClearOrSaveResult(result);
- break;
- }
-
- if (pset.gset_prefix)
- {
- /* StoreQueryTuple will complain if not exactly one row
*/
- OK = StoreQueryTuple(result);
- ClearOrSaveResult(result);
- break;
- }
-
- /*
- * Note we do not deal with \gdesc, \gexec or \crosstabview
modes here
- */
-
- ntuples = PQntuples(result);
- total_tuples += ntuples;
-
- if (ntuples < fetch_count)
- {
- /* this is the last result set, so allow footer
decoration */
- my_popt.topt.stop_table = true;
- }
- else if (fout == stdout && !is_pager)
- {
- /*
- * If query requires multiple result sets, hack to
ensure that
- * only one pager instance is used for the whole mess
- */
- fout = PageOutput(INT_MAX, &(my_popt.topt));
- is_pager = true;
- }
-
- printQuery(result, &my_popt, fout, is_pager, pset.logfile);
-
- ClearOrSaveResult(result);
-
- /* after the first result set, disallow header decoration */
- my_popt.topt.start_table = false;
- my_popt.topt.prior_records += ntuples;
-
- /*
- * Make sure to flush the output stream, so intermediate
results are
- * visible to the client immediately. We check the results
because if
- * the pager dies/exits/etc, there's no sense throwing more
data at
- * it.
- */
- flush_error = fflush(fout);
-
- /*
- * Check if we are at the end, if a cancel was pressed, or if
there
- * were any errors either trying to flush out the results, or
more
- * generally on the output stream at all. If we hit any errors
- * writing things to the stream, we presume $PAGER has
disappeared and
- * stop bothering to pull down more data.
- */
- if (ntuples < fetch_count || cancel_pressed || flush_error ||
- ferror(fout))
- break;
- }
-
- if (pset.gfname)
- {
- /* close \g argument file/pipe */
- if (is_pipe)
- {
- SetShellResultVariables(pclose(fout));
- restore_sigpipe_trap();
- }
- else
- fclose(fout);
- }
- else if (is_pager)
- {
- /* close transient pager */
- ClosePager(fout);
- }
-
- if (OK)
- {
- /*
- * We don't have a PGresult here, and even if we did it
wouldn't have
- * the right row count, so fake SetResultVariables(). In error
cases,
- * we already set the result variables above.
- */
- char buf[32];
-
- SetVariable(pset.vars, "ERROR", "false");
- SetVariable(pset.vars, "SQLSTATE", "00000");
- snprintf(buf, sizeof(buf), INT64_FORMAT, total_tuples);
- SetVariable(pset.vars, "ROW_COUNT", buf);
- }
-
-cleanup:
- if (timing)
- INSTR_TIME_SET_CURRENT(before);
-
- /*
- * We try to close the cursor on either success or failure, but on
failure
- * ignore the result (it's probably just a bleat about being in an
aborted
- * transaction)
- */
- result = PQexec(pset.db, "CLOSE _psql_cursor");
- if (OK)
- {
- OK = AcceptResult(result, true) &&
- (PQresultStatus(result) == PGRES_COMMAND_OK);
- ClearOrSaveResult(result);
- }
- else
- PQclear(result);
-
- if (started_txn)
- {
- result = PQexec(pset.db, OK ? "COMMIT" : "ROLLBACK");
- OK &= AcceptResult(result, true) &&
- (PQresultStatus(result) == PGRES_COMMAND_OK);
- ClearOrSaveResult(result);
- }
-
- if (timing)
- {
- INSTR_TIME_SET_CURRENT(after);
- INSTR_TIME_SUBTRACT(after, before);
- *elapsed_msec += INSTR_TIME_GET_MILLISEC(after);
- }
-
- return OK;
-}
-
-
/*
* Advance the given char pointer over white space and SQL comments.
*/
@@ -2243,43 +2103,6 @@ command_no_begin(const char *query)
}
-/*
- * Check whether the specified command is a SELECT (or VALUES).
- */
-static bool
-is_select_command(const char *query)
-{
- int wordlen;
-
- /*
- * First advance over any whitespace, comments and left parentheses.
- */
- for (;;)
- {
- query = skip_white_space(query);
- if (query[0] == '(')
- query++;
- else
- break;
- }
-
- /*
- * Check word length (since "selectx" is not "select").
- */
- wordlen = 0;
- while (isalpha((unsigned char) query[wordlen]))
- wordlen += PQmblenBounded(&query[wordlen], pset.encoding);
-
- if (wordlen == 6 && pg_strncasecmp(query, "select", 6) == 0)
- return true;
-
- if (wordlen == 6 && pg_strncasecmp(query, "values", 6) == 0)
- return true;
-
- return false;
-}
-
-
/*
* Test if the current user is a database superuser.
*/
diff --git a/src/bin/psql/t/001_basic.pl b/src/bin/psql/t/001_basic.pl
index 95f4e60ab2..62a5d0f383 100644
--- a/src/bin/psql/t/001_basic.pl
+++ b/src/bin/psql/t/001_basic.pl
@@ -161,7 +161,7 @@ psql_like(
'\errverbose with no previous error');
# There are three main ways to run a query that might affect
-# \errverbose: The normal way, using a cursor by setting FETCH_COUNT,
+# \errverbose: The normal way, piecemeal retrieval using FETCH_COUNT,
# and using \gdesc. Test them all.
like(
@@ -184,10 +184,10 @@ like(
"\\set FETCH_COUNT 1\nSELECT error;\n\\errverbose",
on_error_stop => 0))[2],
qr/\A^psql:<stdin>:2: ERROR: .*$
-^LINE 2: SELECT error;$
+^LINE 1: SELECT error;$
^ *^.*$
^psql:<stdin>:3: error: ERROR: [0-9A-Z]{5}: .*$
-^LINE 2: SELECT error;$
+^LINE 1: SELECT error;$
^ *^.*$
^LOCATION: .*$/m,
'\errverbose after FETCH_COUNT query with error');
diff --git a/src/test/regress/expected/psql.out
b/src/test/regress/expected/psql.out
index 13e4f6db7b..aa53f11682 100644
--- a/src/test/regress/expected/psql.out
+++ b/src/test/regress/expected/psql.out
@@ -4754,7 +4754,7 @@ number of rows: 0
last error message: syntax error at end of input
\echo 'last error code:' :LAST_ERROR_SQLSTATE
last error code: 42601
--- check row count for a cursor-fetched query
+-- check row count for a query with chunked results
\set FETCH_COUNT 10
select unique2 from tenk1 order by unique2 limit 19;
unique2
@@ -4786,7 +4786,7 @@ error: false
error code: 00000
\echo 'number of rows:' :ROW_COUNT
number of rows: 19
--- cursor-fetched query with an error after the first group
+-- chunked results with an error after the first chunk
select 1/(15-unique2) from tenk1 order by unique2 limit 19;
?column?
----------
@@ -4800,6 +4800,11 @@ select 1/(15-unique2) from tenk1 order by unique2 limit
19;
0
0
0
+ 0
+ 0
+ 0
+ 0
+ 1
ERROR: division by zero
\echo 'error:' :ERROR
error: true
diff --git a/src/test/regress/sql/psql.sql b/src/test/regress/sql/psql.sql
index 695c72d866..3c4e6962ba 100644
--- a/src/test/regress/sql/psql.sql
+++ b/src/test/regress/sql/psql.sql
@@ -1160,14 +1160,14 @@ SELECT 4 AS \gdesc
\echo 'last error message:' :LAST_ERROR_MESSAGE
\echo 'last error code:' :LAST_ERROR_SQLSTATE
--- check row count for a cursor-fetched query
+-- check row count for a query with chunked results
\set FETCH_COUNT 10
select unique2 from tenk1 order by unique2 limit 19;
\echo 'error:' :ERROR
\echo 'error code:' :SQLSTATE
\echo 'number of rows:' :ROW_COUNT
--- cursor-fetched query with an error after the first group
+-- chunked results with an error after the first chunk
select 1/(15-unique2) from tenk1 order by unique2 limit 19;
\echo 'error:' :ERROR
\echo 'error code:' :SQLSTATE
--
2.34.1
