agora inbox for pgsql-hackers@postgresql.org
help / color / mirror / Atom feedFrom: Nathan Bossart <nathandbossart@gmail.com>
To: Jacob Champion <jacob.champion@enterprisedb.com>
Cc: pgsql-hackers@postgresql.org
Subject: alert clients when prepared statements are deallocated
Date: Fri, 29 May 2026 11:33:37 -0500
Message-ID: <ahm_4eOKkkKJ3Gds@nathan> (raw)
(Moving to a new thread since this seems like an independent feature.
Original discussion can be found here:
https://postgr.es/m/ahXE28klgxIJXBLq%40nathan)
When trying to take our own advice and teach the frontend LO interface to
use prepared statements instead of PQfn(), I discovered a couple of
problems. The biggest problem is that clients aren't alerted when a
prepared statement is deallocated with DISCARD or DEALLOCATE. Since this
seems like a general problem that affects more than just libpq's LO
functions, I'm seeing whether it makes sense to add some sort of
notification mechanism so that clients can re-prepare as needed. Some
initial discussion about the work-in-progress patch (which I've attached
again here) follows:
On Fri, May 29, 2026 at 11:10:58AM -0500, Nathan Bossart wrote:
> On Fri, May 29, 2026 at 08:43:07AM -0700, Jacob Champion wrote:
>> On Fri, May 29, 2026 at 8:14 AM Nathan Bossart <nathandbossart@gmail.com> wrote:
>>> Here is a work-in-progress patch set that goes this direction.
>>
>> At a high level, I think advertising support for a single new message
>> needs to be done in a protocol extension rather than a minor version
>> bump.
>
> WFM
>
>>> This
>>> introduces a callback mechanism in libpq that is used to handle statement
>>> deallocation notifications. Older servers/clients fall back to
>>> PQexecParams(), which is slower, but the alternative is to leave PQnfn()
>>> and related code around indefinitely.
>>
>> IMO there's no hurry in getting rid of that path. If we decide to go
>> this direction, a fallback to PQnfn() seems like it'd fine for a few
>> releases; we could eventually swap to a PQexecParams() fallback and
>> get rid of the extra code once the older servers have aged out.
>
> That's fine with me, too.
>
>>> I'm wondering whether this new message type is general enough. For
>>> example, perhaps we could make an extensible message type for tracking
>>> various things. And I want to ensure this is useful for other clients,
>>> too.
>>
>> If it's just a general notification message, what does negotiating
>> "support" mean? Is best-effort notification okay, if the client has no
>> idea what a future message type means, or if the server doesn't send
>> the specific type of message the client is hoping for?
>
> That's what I had in mind. But if we don't have anything specific in mind
> that this mechanism could be extended to support, maybe we shouldn't
> bother. Especially if we can just add protocol extensions as necessary.
>
>> (In general, I'm kind of down on the "notify the client that X
>> happened" method of working around architectural issues. Maybe that's
>> what we need to move this specific part forward, but it doesn't feel
>> like a long-term solution and I don't know that we need to genericize
>> it without a solid set of use cases.)
>
> I'm certainly open to other ideas, but I'm afraid this is the best I've
> come up with in my admittedly limited time thinking about the problem.
--
nathan
From ed962c55faf3b6ef28af6672591f460ad2289273 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Thu, 28 May 2026 15:42:20 -0500
Subject: [PATCH v2 1/3] tell client when prep stmts are deallocated
---
src/backend/commands/prepare.c | 30 +++++++++++++
src/include/libpq/pqcomm.h | 2 +-
src/include/libpq/protocol.h | 1 +
src/interfaces/libpq/exports.txt | 1 +
src/interfaces/libpq/fe-connect.c | 30 +++++++++++++
src/interfaces/libpq/fe-protocol3.c | 43 +++++++++++++++++++
src/interfaces/libpq/fe-trace.c | 10 +++++
src/interfaces/libpq/libpq-fe.h | 6 +++
src/interfaces/libpq/libpq-int.h | 2 +
.../modules/libpq_pipeline/libpq_pipeline.c | 12 +++---
.../libpq_pipeline/traces/prepared.trace | 1 +
11 files changed, 131 insertions(+), 7 deletions(-)
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 876aad2100a..4ca85b10f9e 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -26,6 +26,9 @@
#include "commands/explain_state.h"
#include "commands/prepare.h"
#include "funcapi.h"
+#include "libpq/libpq-be.h"
+#include "libpq/pqformat.h"
+#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
@@ -512,6 +515,27 @@ DeallocateQuery(DeallocateStmt *stmt)
DropAllPreparedStatements();
}
+/*
+ * Tell the client that a prepared statement has been deallocated. Pass an
+ * empty string to indicate that all statements were deallocated.
+ *
+ * This is only sent to clients that are using protocol version 3.3 or later.
+ */
+static void
+SendStmtDeallocMsg(const char *name)
+{
+ StringInfoData buf;
+
+ if (whereToSendOutput != DestRemote)
+ return;
+ if (!MyProcPort || MyProcPort->proto < PG_PROTOCOL(3, 3))
+ return;
+
+ pq_beginmessage(&buf, PqMsg_PrepStmtDeallocated);
+ pq_sendstring(&buf, name);
+ pq_endmessage(&buf);
+}
+
/*
* Internal version of DEALLOCATE
*
@@ -530,6 +554,9 @@ DropPreparedStatement(const char *stmt_name, bool showError)
/* Release the plancache entry */
DropCachedPlan(entry->plansource);
+ /* Alert the client */
+ SendStmtDeallocMsg(entry->stmt_name);
+
/* Now we can remove the hash table entry */
hash_search(prepared_queries, entry->stmt_name, HASH_REMOVE, NULL);
}
@@ -548,6 +575,9 @@ DropAllPreparedStatements(void)
if (!prepared_queries)
return;
+ /* Alert the client */
+ SendStmtDeallocMsg("");
+
/* walk over cache */
hash_seq_init(&seq, prepared_queries);
while ((entry = hash_seq_search(&seq)) != NULL)
diff --git a/src/include/libpq/pqcomm.h b/src/include/libpq/pqcomm.h
index a29c9c94d79..28e7944cdf4 100644
--- a/src/include/libpq/pqcomm.h
+++ b/src/include/libpq/pqcomm.h
@@ -92,7 +92,7 @@ is_unixsock_path(const char *path)
* The earliest and latest frontend/backend protocol version supported.
*/
#define PG_PROTOCOL_EARLIEST PG_PROTOCOL(3,0)
-#define PG_PROTOCOL_LATEST PG_PROTOCOL(3,2)
+#define PG_PROTOCOL_LATEST PG_PROTOCOL(3,3)
/*
* Reserved protocol numbers, which have special semantics:
diff --git a/src/include/libpq/protocol.h b/src/include/libpq/protocol.h
index eae8f0e7238..7ea331f7210 100644
--- a/src/include/libpq/protocol.h
+++ b/src/include/libpq/protocol.h
@@ -53,6 +53,7 @@
#define PqMsg_FunctionCallResponse 'V'
#define PqMsg_CopyBothResponse 'W'
#define PqMsg_ReadyForQuery 'Z'
+#define PqMsg_PrepStmtDeallocated 'i'
#define PqMsg_NoData 'n'
#define PqMsg_PortalSuspended 's'
#define PqMsg_ParameterDescription 't'
diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt
index 1e3d5bd5867..effd73ca3e6 100644
--- a/src/interfaces/libpq/exports.txt
+++ b/src/interfaces/libpq/exports.txt
@@ -211,3 +211,4 @@ PQdefaultAuthDataHook 208
PQfullProtocolVersion 209
appendPQExpBufferVA 210
PQgetThreadLock 211
+PQaddPrepStmtDeallocCallback 212
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 4272d386e64..5e41c21c6f6 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -8374,6 +8374,11 @@ pqParseProtocolVersion(const char *value, ProtocolVersion *result, PGconn *conn,
*result = PG_PROTOCOL(3, 2);
return true;
}
+ if (strcmp(value, "3.3") == 0)
+ {
+ *result = PG_PROTOCOL(3, 3);
+ return true;
+ }
libpq_append_conn_error(conn, "invalid %s value: \"%s\"",
context, value);
@@ -8426,3 +8431,28 @@ PQgetThreadLock(void)
Assert(pg_g_threadlock);
return pg_g_threadlock;
}
+
+/*
+ * Adds a prepared statement deallocation callback to the connection's list of
+ * callbacks. These are invoked when the server sends us
+ * PqMsg_PrepStmtDeallocated messages.
+ */
+bool
+PQaddPrepStmtDeallocCallback(PGconn *conn, PQprepStmtDeallocCallback cb)
+{
+ if (!conn)
+ return false;
+
+ /* Add to end to preserve registration order */
+ for (int i = 0; i < lengthof(conn->prepStmtDeallocCallbacks); i++)
+ {
+ if (conn->prepStmtDeallocCallbacks[i])
+ continue;
+
+ conn->prepStmtDeallocCallbacks[i] = cb;
+ return true;
+ }
+
+ libpq_append_conn_error(conn, "maximum number of prepared statement deallocation callbacks already registered");
+ return false;
+}
diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 840e018cd18..0407d10362d 100644
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -61,6 +61,32 @@ static size_t build_startup_packet(const PGconn *conn, char *packet,
const PQEnvironmentOption *options);
+/*
+ * Attempt to read a PrepStmtDeallocated message and invoke the connection's
+ * registered callbacks. This is possible in several places, so we break it
+ * out as a subroutine.
+ *
+ * Entry: 'i' message type and length have already been consumed.
+ * Exit: returns 0 if successfully consumed message and invoked callbacks, or
+ * EOF if not enough data.
+ */
+static int
+getPrepStmtDeallocated(PGconn *conn)
+{
+ if (pqGets(&conn->workBuffer, conn))
+ return EOF;
+
+ for (int i = 0; i < lengthof(conn->prepStmtDeallocCallbacks); i++)
+ {
+ if (!conn->prepStmtDeallocCallbacks[i])
+ break;
+
+ (conn->prepStmtDeallocCallbacks[i]) (conn, conn->workBuffer.data);
+ }
+
+ return 0;
+}
+
/*
* parseInput: if appropriate, parse input data from backend
* until input is exhausted or a stopping state is reached.
@@ -184,6 +210,11 @@ pqParseInput3(PGconn *conn)
if (getParameterStatus(conn))
return;
}
+ else if (id == PqMsg_PrepStmtDeallocated)
+ {
+ if (getPrepStmtDeallocated(conn))
+ return;
+ }
else
{
/* Any other case is unexpected and we summarily skip it */
@@ -305,6 +336,10 @@ pqParseInput3(PGconn *conn)
if (getParameterStatus(conn))
return;
break;
+ case PqMsg_PrepStmtDeallocated:
+ if (getPrepStmtDeallocated(conn))
+ return;
+ break;
case PqMsg_BackendKeyData:
/*
@@ -1905,6 +1940,10 @@ getCopyDataMessage(PGconn *conn)
if (getParameterStatus(conn))
return 0;
break;
+ case PqMsg_PrepStmtDeallocated:
+ if (getPrepStmtDeallocated(conn))
+ return 0;
+ break;
case PqMsg_CopyData:
return msgLength;
case PqMsg_CopyDone:
@@ -2409,6 +2448,10 @@ pqFunctionCall3(PGconn *conn, Oid fnid,
if (getParameterStatus(conn))
continue;
break;
+ case PqMsg_PrepStmtDeallocated:
+ if (getPrepStmtDeallocated(conn))
+ continue;
+ break;
default:
/* The backend violates the protocol. */
libpq_append_conn_error(conn, "protocol error: id=0x%x", id);
diff --git a/src/interfaces/libpq/fe-trace.c b/src/interfaces/libpq/fe-trace.c
index c348b08c39b..e9f734187a2 100644
--- a/src/interfaces/libpq/fe-trace.c
+++ b/src/interfaces/libpq/fe-trace.c
@@ -543,6 +543,13 @@ pqTraceOutput_ParameterStatus(FILE *f, const char *message, int *cursor)
pqTraceOutputString(f, message, cursor, false);
}
+static void
+pqTraceOutput_PrepStmtDeallocated(FILE *f, const char *message, int *cursor)
+{
+ fprintf(f, "PrepStmtDeallocated\t");
+ pqTraceOutputString(f, message, cursor, false);
+}
+
static void
pqTraceOutput_ParameterDescription(FILE *f, const char *message, int *cursor, bool regress)
{
@@ -793,6 +800,9 @@ pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer)
else
pqTraceOutput_ParameterStatus(conn->Pfdebug, message, &logCursor);
break;
+ case PqMsg_PrepStmtDeallocated:
+ pqTraceOutput_PrepStmtDeallocated(conn->Pfdebug, message, &logCursor);
+ break;
case PqMsg_ParameterDescription:
pqTraceOutput_ParameterDescription(conn->Pfdebug, message, &logCursor, regress);
break;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 8ecb9b4a4c7..c57bb8806cf 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -486,6 +486,12 @@ typedef void (*pgthreadlock_t) (int acquire);
extern pgthreadlock_t PQregisterThreadLock(pgthreadlock_t newhandler);
extern pgthreadlock_t PQgetThreadLock(void);
+/* callbacks for prepared statement deallocation notifications */
+typedef void (*PQprepStmtDeallocCallback) (PGconn *conn, const char *name);
+
+extern bool PQaddPrepStmtDeallocCallback(PGconn *conn,
+ PQprepStmtDeallocCallback cb);
+
/* === in fe-trace.c === */
extern void PQtrace(PGconn *conn, FILE *debug_port);
extern void PQuntrace(PGconn *conn);
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 461b39620c3..7eca941ddcc 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -532,6 +532,8 @@ struct pg_conn
void (*cleanup_async_auth) (PGconn *conn);
pgsocket altsock; /* alternative socket for client to poll */
+ /* Callbacks for prep stmt deallocs (16 ought to be enough for anybody) */
+ PQprepStmtDeallocCallback prepStmtDeallocCallbacks[16];
/* Transient state needed while establishing connection */
PGTargetServerType target_server_type; /* desired session properties */
diff --git a/src/test/modules/libpq_pipeline/libpq_pipeline.c b/src/test/modules/libpq_pipeline/libpq_pipeline.c
index ee3e2ec7570..b61f33e7cd9 100644
--- a/src/test/modules/libpq_pipeline/libpq_pipeline.c
+++ b/src/test/modules/libpq_pipeline/libpq_pipeline.c
@@ -1363,7 +1363,7 @@ test_protocol_version(PGconn *conn)
Assert(max_protocol_version_index >= 0);
/*
- * Test default protocol_version (GREASE - should negotiate down to 3.2)
+ * Test default protocol_version (GREASE - should negotiate down to 3.3)
*/
vals[max_protocol_version_index] = "";
conn = PQconnectdbParams(keywords, vals, false);
@@ -1373,8 +1373,8 @@ test_protocol_version(PGconn *conn)
PQerrorMessage(conn));
protocol_version = PQfullProtocolVersion(conn);
- if (protocol_version != 30002)
- pg_fatal("expected 30002, got %d", protocol_version);
+ if (protocol_version != 30003)
+ pg_fatal("expected 30003, got %d", protocol_version);
PQfinish(conn);
@@ -1423,7 +1423,7 @@ test_protocol_version(PGconn *conn)
PQfinish(conn);
/*
- * Test max_protocol_version=latest. 'latest' currently means '3.2'.
+ * Test max_protocol_version=latest. 'latest' currently means '3.3'.
*/
vals[max_protocol_version_index] = "latest";
conn = PQconnectdbParams(keywords, vals, false);
@@ -1433,8 +1433,8 @@ test_protocol_version(PGconn *conn)
PQerrorMessage(conn));
protocol_version = PQfullProtocolVersion(conn);
- if (protocol_version != 30002)
- pg_fatal("expected 30002, got %d", protocol_version);
+ if (protocol_version != 30003)
+ pg_fatal("expected 30003, got %d", protocol_version);
PQfinish(conn);
diff --git a/src/test/modules/libpq_pipeline/traces/prepared.trace b/src/test/modules/libpq_pipeline/traces/prepared.trace
index aeb5de109e0..5d36fb0056d 100644
--- a/src/test/modules/libpq_pipeline/traces/prepared.trace
+++ b/src/test/modules/libpq_pipeline/traces/prepared.trace
@@ -7,6 +7,7 @@ B 113 RowDescription 4 "?column?" NNNN 0 NNNN 4 -1 0 "?column?" NNNN 0 NNNN 655
B 5 ReadyForQuery I
F 16 Close S "select_one"
F 4 Sync
+B 15 PrepStmtDeallocated "select_one"
B 4 CloseComplete
B 5 ReadyForQuery I
F 16 Describe S "select_one"
--
2.50.1 (Apple Git-155)
Attachments:
[text/plain] v2-0001-tell-client-when-prep-stmts-are-deallocated.patch (12.1K, ../ahm_4eOKkkKJ3Gds@nathan/2-v2-0001-tell-client-when-prep-stmts-are-deallocated.patch)
download | inline diff:
From ed962c55faf3b6ef28af6672591f460ad2289273 Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathan@postgresql.org>
Date: Thu, 28 May 2026 15:42:20 -0500
Subject: [PATCH v2 1/3] tell client when prep stmts are deallocated
---
src/backend/commands/prepare.c | 30 +++++++++++++
src/include/libpq/pqcomm.h | 2 +-
src/include/libpq/protocol.h | 1 +
src/interfaces/libpq/exports.txt | 1 +
src/interfaces/libpq/fe-connect.c | 30 +++++++++++++
src/interfaces/libpq/fe-protocol3.c | 43 +++++++++++++++++++
src/interfaces/libpq/fe-trace.c | 10 +++++
src/interfaces/libpq/libpq-fe.h | 6 +++
src/interfaces/libpq/libpq-int.h | 2 +
.../modules/libpq_pipeline/libpq_pipeline.c | 12 +++---
.../libpq_pipeline/traces/prepared.trace | 1 +
11 files changed, 131 insertions(+), 7 deletions(-)
diff --git a/src/backend/commands/prepare.c b/src/backend/commands/prepare.c
index 876aad2100a..4ca85b10f9e 100644
--- a/src/backend/commands/prepare.c
+++ b/src/backend/commands/prepare.c
@@ -26,6 +26,9 @@
#include "commands/explain_state.h"
#include "commands/prepare.h"
#include "funcapi.h"
+#include "libpq/libpq-be.h"
+#include "libpq/pqformat.h"
+#include "miscadmin.h"
#include "nodes/nodeFuncs.h"
#include "parser/parse_coerce.h"
#include "parser/parse_collate.h"
@@ -512,6 +515,27 @@ DeallocateQuery(DeallocateStmt *stmt)
DropAllPreparedStatements();
}
+/*
+ * Tell the client that a prepared statement has been deallocated. Pass an
+ * empty string to indicate that all statements were deallocated.
+ *
+ * This is only sent to clients that are using protocol version 3.3 or later.
+ */
+static void
+SendStmtDeallocMsg(const char *name)
+{
+ StringInfoData buf;
+
+ if (whereToSendOutput != DestRemote)
+ return;
+ if (!MyProcPort || MyProcPort->proto < PG_PROTOCOL(3, 3))
+ return;
+
+ pq_beginmessage(&buf, PqMsg_PrepStmtDeallocated);
+ pq_sendstring(&buf, name);
+ pq_endmessage(&buf);
+}
+
/*
* Internal version of DEALLOCATE
*
@@ -530,6 +554,9 @@ DropPreparedStatement(const char *stmt_name, bool showError)
/* Release the plancache entry */
DropCachedPlan(entry->plansource);
+ /* Alert the client */
+ SendStmtDeallocMsg(entry->stmt_name);
+
/* Now we can remove the hash table entry */
hash_search(prepared_queries, entry->stmt_name, HASH_REMOVE, NULL);
}
@@ -548,6 +575,9 @@ DropAllPreparedStatements(void)
if (!prepared_queries)
return;
+ /* Alert the client */
+ SendStmtDeallocMsg("");
+
/* walk over cache */
hash_seq_init(&seq, prepared_queries);
while ((entry = hash_seq_search(&seq)) != NULL)
diff --git a/src/include/libpq/pqcomm.h b/src/include/libpq/pqcomm.h
index a29c9c94d79..28e7944cdf4 100644
--- a/src/include/libpq/pqcomm.h
+++ b/src/include/libpq/pqcomm.h
@@ -92,7 +92,7 @@ is_unixsock_path(const char *path)
* The earliest and latest frontend/backend protocol version supported.
*/
#define PG_PROTOCOL_EARLIEST PG_PROTOCOL(3,0)
-#define PG_PROTOCOL_LATEST PG_PROTOCOL(3,2)
+#define PG_PROTOCOL_LATEST PG_PROTOCOL(3,3)
/*
* Reserved protocol numbers, which have special semantics:
diff --git a/src/include/libpq/protocol.h b/src/include/libpq/protocol.h
index eae8f0e7238..7ea331f7210 100644
--- a/src/include/libpq/protocol.h
+++ b/src/include/libpq/protocol.h
@@ -53,6 +53,7 @@
#define PqMsg_FunctionCallResponse 'V'
#define PqMsg_CopyBothResponse 'W'
#define PqMsg_ReadyForQuery 'Z'
+#define PqMsg_PrepStmtDeallocated 'i'
#define PqMsg_NoData 'n'
#define PqMsg_PortalSuspended 's'
#define PqMsg_ParameterDescription 't'
diff --git a/src/interfaces/libpq/exports.txt b/src/interfaces/libpq/exports.txt
index 1e3d5bd5867..effd73ca3e6 100644
--- a/src/interfaces/libpq/exports.txt
+++ b/src/interfaces/libpq/exports.txt
@@ -211,3 +211,4 @@ PQdefaultAuthDataHook 208
PQfullProtocolVersion 209
appendPQExpBufferVA 210
PQgetThreadLock 211
+PQaddPrepStmtDeallocCallback 212
diff --git a/src/interfaces/libpq/fe-connect.c b/src/interfaces/libpq/fe-connect.c
index 4272d386e64..5e41c21c6f6 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -8374,6 +8374,11 @@ pqParseProtocolVersion(const char *value, ProtocolVersion *result, PGconn *conn,
*result = PG_PROTOCOL(3, 2);
return true;
}
+ if (strcmp(value, "3.3") == 0)
+ {
+ *result = PG_PROTOCOL(3, 3);
+ return true;
+ }
libpq_append_conn_error(conn, "invalid %s value: \"%s\"",
context, value);
@@ -8426,3 +8431,28 @@ PQgetThreadLock(void)
Assert(pg_g_threadlock);
return pg_g_threadlock;
}
+
+/*
+ * Adds a prepared statement deallocation callback to the connection's list of
+ * callbacks. These are invoked when the server sends us
+ * PqMsg_PrepStmtDeallocated messages.
+ */
+bool
+PQaddPrepStmtDeallocCallback(PGconn *conn, PQprepStmtDeallocCallback cb)
+{
+ if (!conn)
+ return false;
+
+ /* Add to end to preserve registration order */
+ for (int i = 0; i < lengthof(conn->prepStmtDeallocCallbacks); i++)
+ {
+ if (conn->prepStmtDeallocCallbacks[i])
+ continue;
+
+ conn->prepStmtDeallocCallbacks[i] = cb;
+ return true;
+ }
+
+ libpq_append_conn_error(conn, "maximum number of prepared statement deallocation callbacks already registered");
+ return false;
+}
diff --git a/src/interfaces/libpq/fe-protocol3.c b/src/interfaces/libpq/fe-protocol3.c
index 840e018cd18..0407d10362d 100644
--- a/src/interfaces/libpq/fe-protocol3.c
+++ b/src/interfaces/libpq/fe-protocol3.c
@@ -61,6 +61,32 @@ static size_t build_startup_packet(const PGconn *conn, char *packet,
const PQEnvironmentOption *options);
+/*
+ * Attempt to read a PrepStmtDeallocated message and invoke the connection's
+ * registered callbacks. This is possible in several places, so we break it
+ * out as a subroutine.
+ *
+ * Entry: 'i' message type and length have already been consumed.
+ * Exit: returns 0 if successfully consumed message and invoked callbacks, or
+ * EOF if not enough data.
+ */
+static int
+getPrepStmtDeallocated(PGconn *conn)
+{
+ if (pqGets(&conn->workBuffer, conn))
+ return EOF;
+
+ for (int i = 0; i < lengthof(conn->prepStmtDeallocCallbacks); i++)
+ {
+ if (!conn->prepStmtDeallocCallbacks[i])
+ break;
+
+ (conn->prepStmtDeallocCallbacks[i]) (conn, conn->workBuffer.data);
+ }
+
+ return 0;
+}
+
/*
* parseInput: if appropriate, parse input data from backend
* until input is exhausted or a stopping state is reached.
@@ -184,6 +210,11 @@ pqParseInput3(PGconn *conn)
if (getParameterStatus(conn))
return;
}
+ else if (id == PqMsg_PrepStmtDeallocated)
+ {
+ if (getPrepStmtDeallocated(conn))
+ return;
+ }
else
{
/* Any other case is unexpected and we summarily skip it */
@@ -305,6 +336,10 @@ pqParseInput3(PGconn *conn)
if (getParameterStatus(conn))
return;
break;
+ case PqMsg_PrepStmtDeallocated:
+ if (getPrepStmtDeallocated(conn))
+ return;
+ break;
case PqMsg_BackendKeyData:
/*
@@ -1905,6 +1940,10 @@ getCopyDataMessage(PGconn *conn)
if (getParameterStatus(conn))
return 0;
break;
+ case PqMsg_PrepStmtDeallocated:
+ if (getPrepStmtDeallocated(conn))
+ return 0;
+ break;
case PqMsg_CopyData:
return msgLength;
case PqMsg_CopyDone:
@@ -2409,6 +2448,10 @@ pqFunctionCall3(PGconn *conn, Oid fnid,
if (getParameterStatus(conn))
continue;
break;
+ case PqMsg_PrepStmtDeallocated:
+ if (getPrepStmtDeallocated(conn))
+ continue;
+ break;
default:
/* The backend violates the protocol. */
libpq_append_conn_error(conn, "protocol error: id=0x%x", id);
diff --git a/src/interfaces/libpq/fe-trace.c b/src/interfaces/libpq/fe-trace.c
index c348b08c39b..e9f734187a2 100644
--- a/src/interfaces/libpq/fe-trace.c
+++ b/src/interfaces/libpq/fe-trace.c
@@ -543,6 +543,13 @@ pqTraceOutput_ParameterStatus(FILE *f, const char *message, int *cursor)
pqTraceOutputString(f, message, cursor, false);
}
+static void
+pqTraceOutput_PrepStmtDeallocated(FILE *f, const char *message, int *cursor)
+{
+ fprintf(f, "PrepStmtDeallocated\t");
+ pqTraceOutputString(f, message, cursor, false);
+}
+
static void
pqTraceOutput_ParameterDescription(FILE *f, const char *message, int *cursor, bool regress)
{
@@ -793,6 +800,9 @@ pqTraceOutputMessage(PGconn *conn, const char *message, bool toServer)
else
pqTraceOutput_ParameterStatus(conn->Pfdebug, message, &logCursor);
break;
+ case PqMsg_PrepStmtDeallocated:
+ pqTraceOutput_PrepStmtDeallocated(conn->Pfdebug, message, &logCursor);
+ break;
case PqMsg_ParameterDescription:
pqTraceOutput_ParameterDescription(conn->Pfdebug, message, &logCursor, regress);
break;
diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 8ecb9b4a4c7..c57bb8806cf 100644
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -486,6 +486,12 @@ typedef void (*pgthreadlock_t) (int acquire);
extern pgthreadlock_t PQregisterThreadLock(pgthreadlock_t newhandler);
extern pgthreadlock_t PQgetThreadLock(void);
+/* callbacks for prepared statement deallocation notifications */
+typedef void (*PQprepStmtDeallocCallback) (PGconn *conn, const char *name);
+
+extern bool PQaddPrepStmtDeallocCallback(PGconn *conn,
+ PQprepStmtDeallocCallback cb);
+
/* === in fe-trace.c === */
extern void PQtrace(PGconn *conn, FILE *debug_port);
extern void PQuntrace(PGconn *conn);
diff --git a/src/interfaces/libpq/libpq-int.h b/src/interfaces/libpq/libpq-int.h
index 461b39620c3..7eca941ddcc 100644
--- a/src/interfaces/libpq/libpq-int.h
+++ b/src/interfaces/libpq/libpq-int.h
@@ -532,6 +532,8 @@ struct pg_conn
void (*cleanup_async_auth) (PGconn *conn);
pgsocket altsock; /* alternative socket for client to poll */
+ /* Callbacks for prep stmt deallocs (16 ought to be enough for anybody) */
+ PQprepStmtDeallocCallback prepStmtDeallocCallbacks[16];
/* Transient state needed while establishing connection */
PGTargetServerType target_server_type; /* desired session properties */
diff --git a/src/test/modules/libpq_pipeline/libpq_pipeline.c b/src/test/modules/libpq_pipeline/libpq_pipeline.c
index ee3e2ec7570..b61f33e7cd9 100644
--- a/src/test/modules/libpq_pipeline/libpq_pipeline.c
+++ b/src/test/modules/libpq_pipeline/libpq_pipeline.c
@@ -1363,7 +1363,7 @@ test_protocol_version(PGconn *conn)
Assert(max_protocol_version_index >= 0);
/*
- * Test default protocol_version (GREASE - should negotiate down to 3.2)
+ * Test default protocol_version (GREASE - should negotiate down to 3.3)
*/
vals[max_protocol_version_index] = "";
conn = PQconnectdbParams(keywords, vals, false);
@@ -1373,8 +1373,8 @@ test_protocol_version(PGconn *conn)
PQerrorMessage(conn));
protocol_version = PQfullProtocolVersion(conn);
- if (protocol_version != 30002)
- pg_fatal("expected 30002, got %d", protocol_version);
+ if (protocol_version != 30003)
+ pg_fatal("expected 30003, got %d", protocol_version);
PQfinish(conn);
@@ -1423,7 +1423,7 @@ test_protocol_version(PGconn *conn)
PQfinish(conn);
/*
- * Test max_protocol_version=latest. 'latest' currently means '3.2'.
+ * Test max_protocol_version=latest. 'latest' currently means '3.3'.
*/
vals[max_protocol_version_index] = "latest";
conn = PQconnectdbParams(keywords, vals, false);
@@ -1433,8 +1433,8 @@ test_protocol_version(PGconn *conn)
PQerrorMessage(conn));
protocol_version = PQfullProtocolVersion(conn);
- if (protocol_version != 30002)
- pg_fatal("expected 30002, got %d", protocol_version);
+ if (protocol_version != 30003)
+ pg_fatal("expected 30003, got %d", protocol_version);
PQfinish(conn);
diff --git a/src/test/modules/libpq_pipeline/traces/prepared.trace b/src/test/modules/libpq_pipeline/traces/prepared.trace
index aeb5de109e0..5d36fb0056d 100644
--- a/src/test/modules/libpq_pipeline/traces/prepared.trace
+++ b/src/test/modules/libpq_pipeline/traces/prepared.trace
@@ -7,6 +7,7 @@ B 113 RowDescription 4 "?column?" NNNN 0 NNNN 4 -1 0 "?column?" NNNN 0 NNNN 655
B 5 ReadyForQuery I
F 16 Close S "select_one"
F 4 Sync
+B 15 PrepStmtDeallocated "select_one"
B 4 CloseComplete
B 5 ReadyForQuery I
F 16 Describe S "select_one"
--
2.50.1 (Apple Git-155)
view thread (13+ messages) latest in thread
Message-ID: <ahm_4eOKkkKJ3Gds@nathan>
Permalink: ../ahm_4eOKkkKJ3Gds@nathan/
Also on: postgresql.org/message-id/ahm_4eOKkkKJ3Gds@nathan
reply
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: nathandbossart@gmail.com, jacob.champion@enterprisedb.com
Subject: Re: alert clients when prepared statements are deallocated
In-Reply-To: <ahm_4eOKkkKJ3Gds@nathan>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by agora; see mirroring instructions
for how to clone and mirror all data and code used for this inbox