postgres.git / summary / log / commit / refs

commit    cfd6cbcf9be078fbdf9587014231a5772039b386
Author:   Michael Paquier <michael@paquier.xyz>
Date:     Mon Dec 23 03:48:10 2024 +0000

    Fix memory leak in pgoutput with publication list cache
    
    The pgoutput module caches publication names in a list and frees it upon
    invalidation.  However, the code forgot to free the actual publication
    names within the list elements, as publication names are pstrdup()'d in
    GetPublication().  This would cause memory to leak in
    CacheMemoryContext, bloating it over time as this context is not
    cleaned.
    
    This is a problem for WAL senders running for a long time, as an
    accumulation of invalidation requests would bloat its cache memory
    usage.  A second case, where this leak is easier to see, involves a
    backend calling SQL functions like pg_logical_slot_{get,peek}_changes()
    which create a new decoding context with each execution.  More
    publications create more bloat.
    
    To address this, this commit adds a new memory context within the
    logical decoding context and resets it each time the publication names
    cache is invalidated, based on a suggestion from Amit Kapila.  This
    ensures that the lifespan of the publication names aligns with that of
    the logical decoding context.
    
    Contrary to the HEAD-only commit f0c569d71515 that has changed
    PGOutputData to track this new child memory context, the context is
    tracked with a static variable whose state is reset with a MemoryContext
    reset callback attached to PGOutputData->context, so as ABI
    compatibility is preserved in stable branches.  This approach is based
    on an suggestion from Amit Kapila.
    
    Analyzed-by: Michael Paquier, Jeff Davis
    Author: Masahiko Sawada
    Reviewed-by: Amit Kapila, Michael Paquier, Euler Taveira, Hou Zhijie
    Discussion: https://postgr.es/m/Z0khf9EVMVLOc_YY@paquier.xyz
    Backpatch-through: 13


 src/backend/replication/pgoutput/pgoutput.c | 41 +++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 5 deletions(-)

diff --git a/src/backend/replication/pgoutput/pgoutput.c b/src/backend/replication/pgoutput/pgoutput.c
index df2ea94d468..9fd879ee0c8 100644
--- a/src/backend/replication/pgoutput/pgoutput.c
+++ b/src/backend/replication/pgoutput/pgoutput.c
@@ -65,6 +65,13 @@ static void pgoutput_stream_commit(struct LogicalDecodingContext *ctx,
 static bool publications_valid;
 static bool in_streaming;
 
+/*
+ * Private memory context for publication data, created in
+ * PGOutputData->context when starting pgoutput, and set to NULL when its
+ * parent context is reset via a dedicated MemoryContextCallback.
+ */
+static MemoryContext pubctx = NULL;
+
 static List *LoadPublications(List *pubnames);
 static void publication_invalidation_cb(Datum arg, int cacheid,
 										uint32 hashvalue);
@@ -252,6 +259,15 @@ parse_output_parameters(List *options, PGOutputData *data)
 	}
 }
 
+/*
+ * Callback of PGOutputData->context in charge of cleaning pubctx.
+ */
+static void
+pgoutput_pubctx_reset_callback(void *arg)
+{
+	pubctx = NULL;
+}
+
 /*
  * Initialize this plugin
  */
@@ -261,12 +277,22 @@ pgoutput_startup(LogicalDecodingContext *ctx, OutputPluginOptions *opt,
 {
 	PGOutputData *data = palloc0(sizeof(PGOutputData));
 	static bool publication_callback_registered = false;
+	MemoryContextCallback *mcallback;
 
 	/* Create our memory context for private allocations. */
 	data->context = AllocSetContextCreate(ctx->context,
 										  "logical replication output context",
 										  ALLOCSET_DEFAULT_SIZES);
 
+	Assert(pubctx == NULL);
+	pubctx = AllocSetContextCreate(ctx->context,
+								   "logical replication publication list context",
+								   ALLOCSET_SMALL_SIZES);
+
+	mcallback = palloc0(sizeof(MemoryContextCallback));
+	mcallback->func = pgoutput_pubctx_reset_callback;
+	MemoryContextRegisterResetCallback(ctx->context, mcallback);
+
 	ctx->output_plugin_private = data;
 
 	/* This plugin uses binary protocol. */
@@ -786,8 +812,9 @@ pgoutput_origin_filter(LogicalDecodingContext *ctx,
 /*
  * Shutdown the output plugin.
  *
- * Note, we don't need to clean the data->context as it's child context
- * of the ctx->context so it will be cleaned up by logical decoding machinery.
+ * Note, we don't need to clean the data->context and pubctx as they are
+ * child contexts of the ctx->context so they will be cleaned up by logical
+ * decoding machinery.
  */
 static void
 pgoutput_shutdown(LogicalDecodingContext *ctx)
@@ -797,6 +824,9 @@ pgoutput_shutdown(LogicalDecodingContext *ctx)
 		hash_destroy(RelationSyncCache);
 		RelationSyncCache = NULL;
 	}
+
+	/* Better safe than sorry */
+	pubctx = NULL;
 }
 
 /*
@@ -1071,9 +1101,10 @@ get_rel_sync_entry(PGOutputData *data, Oid relid)
 		/* Reload publications if needed before use. */
 		if (!publications_valid)
 		{
-			oldctx = MemoryContextSwitchTo(CacheMemoryContext);
-			if (data->publications)
-				list_free_deep(data->publications);
+			Assert(pubctx);
+
+			MemoryContextReset(pubctx);
+			oldctx = MemoryContextSwitchTo(pubctx);
 
 			data->publications = LoadPublications(data->publication_names);
 			MemoryContextSwitchTo(oldctx);


[parent: 41eafbb494c9]