From 32d3ed8165f821f6994c95230a9a4b2ff0ce9f12 Mon Sep 17 00:00:00 2001 From: David Rowley Date: Thu, 25 Jul 2024 15:03:28 +1200 Subject: [PATCH] Add path column to pg_backend_memory_contexts view "path" provides a reliable method of determining the parent/child relationships between memory contexts. Previously this could be done in a non-reliable way by writing a recursive query and joining the "parent" and "name" columns. This wasn't reliable as the names were not unique, which could result in joining to the wrong parent. To make this reliable, "path" stores an array of numerical identifiers starting with the identifier for TopLevelMemoryContext. It contains an element for each intermediate parent between that and the current context. Incompatibility: Here we also adjust the "level" column to make it 1-based rather than 0-based. A 1-based level provides a convenient way to access elements in the "path" array. e.g. path[level] gives the identifier for the current context. Identifiers are not stable across multiple evaluations of the view. In an attempt to make these more stable for ad-hoc queries, the identifiers are assigned breadth-first. Contexts closer to TopLevelMemoryContext are less likely to change between queries and during queries. Author: Melih Mutlu Discussion: https://postgr.es/m/CAGPVpCThLyOsj3e_gYEvLoHkr5w=tadDiN_=z2OwsK3VJppeBA@mail.gmail.com Reviewed-by: Andres Freund, Stephen Frost, Atsushi Torikoshi, Reviewed-by: Michael Paquier, Robert Haas, David Rowley --- doc/src/sgml/system-views.sgml | 40 +++++- src/backend/utils/adt/mcxtfuncs.c | 180 +++++++++++++++++++++---- src/include/catalog/catversion.h | 2 +- src/include/catalog/pg_proc.dat | 6 +- src/include/nodes/memnodes.h | 4 +- src/test/regress/expected/rules.out | 3 +- src/test/regress/expected/sysviews.out | 18 ++- src/test/regress/sql/sysviews.sql | 12 +- 8 files changed, 225 insertions(+), 40 deletions(-) diff --git a/doc/src/sgml/system-views.sgml b/doc/src/sgml/system-views.sgml index bdc34cf94e8..a0b692bf1e9 100644 --- a/doc/src/sgml/system-views.sgml +++ b/doc/src/sgml/system-views.sgml @@ -504,7 +504,22 @@ level int4 - Distance from TopMemoryContext in context tree + The 1-based level of the context in the memory context hierarchy. The + level of a context also shows the position of that context in the + path column. + + + + + + path int4[] + + + Array of transient numerical identifiers to describe the memory + context hierarchy. The first element is for + TopMemoryContext, subsequent elements contain + intermediate parents and the final element contains the identifier for + the current context. @@ -561,6 +576,29 @@ read only by superusers or roles with the privileges of the pg_read_all_stats role. + + + Since memory contexts are created and destroyed during the running of a + query, the identifiers stored in the path column + can be unstable between multiple invocations of the view in the same query. + The example below demonstrates an effective usage of this column and + calculates the total number of bytes used by + CacheMemoryContext and all of its children: + + +WITH memory_contexts AS ( + SELECT * FROM pg_backend_memory_contexts +) +SELECT sum(c1.total_bytes) +FROM memory_contexts c1, memory_contexts c2 +WHERE c2.name = 'CacheMemoryContext' +AND c1.path[c2.level] = c2.path[c2.level]; + + + The Common Table Expression is used + to ensure the context IDs in the path column + match between both evaluations of the view. + diff --git a/src/backend/utils/adt/mcxtfuncs.c b/src/backend/utils/adt/mcxtfuncs.c index 10859414848..199e68c1ae5 100644 --- a/src/backend/utils/adt/mcxtfuncs.c +++ b/src/backend/utils/adt/mcxtfuncs.c @@ -19,7 +19,9 @@ #include "mb/pg_wchar.h" #include "storage/proc.h" #include "storage/procarray.h" +#include "utils/array.h" #include "utils/builtins.h" +#include "utils/hsearch.h" /* ---------- * The max bytes for showing identifiers of MemoryContext. @@ -27,47 +29,107 @@ */ #define MEMORY_CONTEXT_IDENT_DISPLAY_SIZE 1024 +/* + * MemoryContextId + * Used for storage of transient identifiers for + * pg_get_backend_memory_contexts. + */ +typedef struct MemoryContextId +{ + MemoryContext context; + int context_id; +} MemoryContextId; + +/* + * get_memory_context_name_and_ident + * Populate *name and *ident from the name and ident from 'context'. + */ +static void +get_memory_context_name_and_ident(MemoryContext context, const char **const name, + const char **const ident) +{ + *name = context->name; + *ident = context->ident; + + /* + * To be consistent with logging output, we label dynahash contexts with + * just the hash table name as with MemoryContextStatsPrint(). + */ + if (ident && strcmp(*name, "dynahash") == 0) + { + *name = *ident; + *ident = NULL; + } +} + +/* + * int_list_to_array + * Convert an IntList to an array of INT4OIDs. + */ +static Datum +int_list_to_array(const List *list) +{ + Datum *datum_array; + int length; + ArrayType *result_array; + + length = list_length(list); + datum_array = (Datum *) palloc(length * sizeof(Datum)); + + foreach_int(i, list) + datum_array[foreach_current_index(i)] = Int32GetDatum(i); + + result_array = construct_array_builtin(datum_array, length, INT4OID); + + return PointerGetDatum(result_array); +} + /* * PutMemoryContextsStatsTupleStore - * One recursion level for pg_get_backend_memory_contexts. + * Add details for the given MemoryContext to 'tupstore'. */ static void PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore, TupleDesc tupdesc, MemoryContext context, - const char *parent, int level) + HTAB *context_id_lookup) { -#define PG_GET_BACKEND_MEMORY_CONTEXTS_COLS 10 +#define PG_GET_BACKEND_MEMORY_CONTEXTS_COLS 11 Datum values[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS]; bool nulls[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS]; MemoryContextCounters stat; - MemoryContext child; + List *path = NIL; const char *name; const char *ident; const char *type; Assert(MemoryContextIsValid(context)); - name = context->name; - ident = context->ident; - /* - * To be consistent with logging output, we label dynahash contexts with - * just the hash table name as with MemoryContextStatsPrint(). + * Figure out the transient context_id of this context and each of its + * ancestors. */ - if (ident && strcmp(name, "dynahash") == 0) + for (MemoryContext cur = context; cur != NULL; cur = cur->parent) { - name = ident; - ident = NULL; + MemoryContextId *entry; + bool found; + + entry = hash_search(context_id_lookup, &cur, HASH_FIND, &found); + + if (!found) + elog(ERROR, "hash table corrupted"); + path = lcons_int(entry->context_id, path); } /* Examine the context itself */ memset(&stat, 0, sizeof(stat)); - (*context->methods->stats) (context, NULL, (void *) &level, &stat, true); + (*context->methods->stats) (context, NULL, NULL, &stat, true); memset(values, 0, sizeof(values)); memset(nulls, 0, sizeof(nulls)); + get_memory_context_name_and_ident(context, &name, &ident); + if (name) values[0] = CStringGetTextDatum(name); else @@ -92,8 +154,15 @@ PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore, else nulls[1] = true; - if (parent) - values[2] = CStringGetTextDatum(parent); + if (context->parent) + { + const char *parent_name, + *parent_ident; + + get_memory_context_name_and_ident(context->parent, &parent_name, + &parent_ident); + values[2] = CStringGetTextDatum(parent_name); + } else nulls[2] = true; @@ -117,19 +186,16 @@ PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore, } values[3] = CStringGetTextDatum(type); - values[4] = Int32GetDatum(level); - values[5] = Int64GetDatum(stat.totalspace); - values[6] = Int64GetDatum(stat.nblocks); - values[7] = Int64GetDatum(stat.freespace); - values[8] = Int64GetDatum(stat.freechunks); - values[9] = Int64GetDatum(stat.totalspace - stat.freespace); - tuplestore_putvalues(tupstore, tupdesc, values, nulls); + values[4] = Int32GetDatum(list_length(path)); /* level */ + values[5] = int_list_to_array(path); + values[6] = Int64GetDatum(stat.totalspace); + values[7] = Int64GetDatum(stat.nblocks); + values[8] = Int64GetDatum(stat.freespace); + values[9] = Int64GetDatum(stat.freechunks); + values[10] = Int64GetDatum(stat.totalspace - stat.freespace); - for (child = context->firstchild; child != NULL; child = child->nextchild) - { - PutMemoryContextsStatsTupleStore(tupstore, tupdesc, - child, name, level + 1); - } + tuplestore_putvalues(tupstore, tupdesc, values, nulls); + list_free(path); } /* @@ -140,10 +206,66 @@ Datum pg_get_backend_memory_contexts(PG_FUNCTION_ARGS) { ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo; + int context_id; + List *contexts; + HASHCTL ctl; + HTAB *context_id_lookup; + + ctl.keysize = sizeof(MemoryContext); + ctl.entrysize = sizeof(MemoryContextId); + ctl.hcxt = CurrentMemoryContext; + + context_id_lookup = hash_create("pg_get_backend_memory_contexts", + 256, + &ctl, + HASH_ELEM | HASH_BLOBS | HASH_CONTEXT); InitMaterializedSRF(fcinfo, 0); - PutMemoryContextsStatsTupleStore(rsinfo->setResult, rsinfo->setDesc, - TopMemoryContext, NULL, 0); + + /* + * Here we use a non-recursive algorithm to visit all MemoryContexts + * starting with TopMemoryContext. The reason we avoid using a recursive + * algorithm is because we want to assign the context_id breadth-first. + * I.e. all contexts at level 1 are assigned IDs before contexts at level + * 2. Because contexts closer to TopMemoryContext are less likely to + * change, this makes the assigned context_id more stable. Otherwise, if + * the first child of TopMemoryContext obtained an additional grandchild, + * the context_id for the second child of TopMemoryContext would change. + */ + contexts = list_make1(TopMemoryContext); + + /* TopMemoryContext will always have a context_id of 1 */ + context_id = 1; + + foreach_ptr(MemoryContextData, cur, contexts) + { + MemoryContextId *entry; + bool found; + + /* + * Record the context_id that we've assigned to each MemoryContext. + * PutMemoryContextsStatsTupleStore needs this to populate the "path" + * column with the parent context_ids. + */ + entry = (MemoryContextId *) hash_search(context_id_lookup, &cur, + HASH_ENTER, &found); + entry->context_id = context_id++; + Assert(!found); + + PutMemoryContextsStatsTupleStore(rsinfo->setResult, + rsinfo->setDesc, + cur, + context_id_lookup); + + /* + * Append all children onto the contexts list so they're processed by + * subsequent iterations. + */ + for (MemoryContext c = cur->firstchild; c != NULL; c = c->nextchild) + contexts = lappend(contexts, c); + } + + hash_destroy(context_id_lookup); return (Datum) 0; } diff --git a/src/include/catalog/catversion.h b/src/include/catalog/catversion.h index 3254e7ab929..4c88ea1034f 100644 --- a/src/include/catalog/catversion.h +++ b/src/include/catalog/catversion.h @@ -57,6 +57,6 @@ */ /* yyyymmddN */ -#define CATALOG_VERSION_NO 202407111 +#define CATALOG_VERSION_NO 202407251 #endif diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat index 73d9cf85826..d14a94b9873 100644 --- a/src/include/catalog/pg_proc.dat +++ b/src/include/catalog/pg_proc.dat @@ -8290,9 +8290,9 @@ proname => 'pg_get_backend_memory_contexts', prorows => '100', proretset => 't', provolatile => 'v', proparallel => 'r', prorettype => 'record', proargtypes => '', - proallargtypes => '{text,text,text,text,int4,int8,int8,int8,int8,int8}', - proargmodes => '{o,o,o,o,o,o,o,o,o,o}', - proargnames => '{name, ident, parent, type, level, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes}', + proallargtypes => '{text,text,text,text,int4,_int4,int8,int8,int8,int8,int8}', + proargmodes => '{o,o,o,o,o,o,o,o,o,o,o}', + proargnames => '{name, ident, parent, type, level, path, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes}', prosrc => 'pg_get_backend_memory_contexts' }, # logging memory contexts of the specified backend diff --git a/src/include/nodes/memnodes.h b/src/include/nodes/memnodes.h index c4c9fd3e3e1..addfbb1ccdf 100644 --- a/src/include/nodes/memnodes.h +++ b/src/include/nodes/memnodes.h @@ -128,8 +128,8 @@ typedef struct MemoryContextData MemoryContext firstchild; /* head of linked list of children */ MemoryContext prevchild; /* previous child of same parent */ MemoryContext nextchild; /* next child of same parent */ - const char *name; /* context name (just for debugging) */ - const char *ident; /* context ID if any (just for debugging) */ + const char *name; /* context name */ + const char *ident; /* context ID if any */ MemoryContextCallback *reset_cbs; /* list of reset/delete callbacks */ } MemoryContextData; diff --git a/src/test/regress/expected/rules.out b/src/test/regress/expected/rules.out index 4c789279e5e..52012806699 100644 --- a/src/test/regress/expected/rules.out +++ b/src/test/regress/expected/rules.out @@ -1308,12 +1308,13 @@ pg_backend_memory_contexts| SELECT name, parent, type, level, + path, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes - FROM pg_get_backend_memory_contexts() pg_get_backend_memory_contexts(name, ident, parent, type, level, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes); + FROM pg_get_backend_memory_contexts() pg_get_backend_memory_contexts(name, ident, parent, type, level, path, total_bytes, total_nblocks, free_bytes, free_chunks, used_bytes); pg_config| SELECT name, setting FROM pg_config() pg_config(name, setting); diff --git a/src/test/regress/expected/sysviews.out b/src/test/regress/expected/sysviews.out index 729620de13c..84b3b64b490 100644 --- a/src/test/regress/expected/sysviews.out +++ b/src/test/regress/expected/sysviews.out @@ -22,10 +22,10 @@ select count(*) >= 0 as ok from pg_available_extensions; -- The entire output of pg_backend_memory_contexts is not stable, -- we test only the existence and basic condition of TopMemoryContext. select type, name, ident, parent, level, total_bytes >= free_bytes - from pg_backend_memory_contexts where level = 0; + from pg_backend_memory_contexts where level = 1; type | name | ident | parent | level | ?column? ----------+------------------+-------+--------+-------+---------- - AllocSet | TopMemoryContext | | | 0 | t + AllocSet | TopMemoryContext | | | 1 | t (1 row) -- We can exercise some MemoryContext type stats functions. Most of the @@ -51,6 +51,20 @@ from pg_backend_memory_contexts where name = 'Caller tuples'; (1 row) rollback; +-- Further sanity checks on pg_backend_memory_contexts. We expect +-- CacheMemoryContext to have multiple children. Ensure that's the case. +with contexts as ( + select * from pg_backend_memory_contexts +) +select count(*) > 1 +from contexts c1, contexts c2 +where c2.name = 'CacheMemoryContext' +and c1.path[c2.level] = c2.path[c2.level]; + ?column? +---------- + t +(1 row) + -- At introduction, pg_config had 23 entries; it may grow select count(*) > 20 as ok from pg_config; ok diff --git a/src/test/regress/sql/sysviews.sql b/src/test/regress/sql/sysviews.sql index 7edac2fde14..15e2a9e7417 100644 --- a/src/test/regress/sql/sysviews.sql +++ b/src/test/regress/sql/sysviews.sql @@ -15,7 +15,7 @@ select count(*) >= 0 as ok from pg_available_extensions; -- The entire output of pg_backend_memory_contexts is not stable, -- we test only the existence and basic condition of TopMemoryContext. select type, name, ident, parent, level, total_bytes >= free_bytes - from pg_backend_memory_contexts where level = 0; + from pg_backend_memory_contexts where level = 1; -- We can exercise some MemoryContext type stats functions. Most of the -- column values are too platform-dependant to display. @@ -32,6 +32,16 @@ select type, name, parent, total_bytes > 0, total_nblocks, free_bytes > 0, free_ from pg_backend_memory_contexts where name = 'Caller tuples'; rollback; +-- Further sanity checks on pg_backend_memory_contexts. We expect +-- CacheMemoryContext to have multiple children. Ensure that's the case. +with contexts as ( + select * from pg_backend_memory_contexts +) +select count(*) > 1 +from contexts c1, contexts c2 +where c2.name = 'CacheMemoryContext' +and c1.path[c2.level] = c2.path[c2.level]; + -- At introduction, pg_config had 23 entries; it may grow select count(*) > 20 as ok from pg_config; -- 2.30.2