mcxtfuncs.c

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/*-------------------------------------------------------------------------
 *
 * mcxtfuncs.c
 *    Functions to show backend memory context.
 *
 * Portions Copyright (c) 1996-2026, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *    src/backend/utils/adt/mcxtfuncs.c
 *
 *-------------------------------------------------------------------------
 */
 
#include "postgres.h"
 
#include "funcapi.h"
#include "mb/pg_wchar.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "storage/procsignal.h"
#include "utils/array.h"
#include "utils/builtins.h"
#include "utils/hsearch.h"
 
/* ----------
 * The max bytes for showing identifiers of MemoryContext.
 * ----------
 */
#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;
 
/*
 * 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 = palloc_array(Datum, length);
 
    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
 *      Add details for the given MemoryContext to 'tupstore'.
 */
static void
PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore,
                                 TupleDesc tupdesc, MemoryContext context,
                                 HTAB *context_id_lookup)
{
#define PG_GET_BACKEND_MEMORY_CONTEXTS_COLS 10
 
    Datum       values[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
    bool        nulls[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
    MemoryContextCounters stat;
    List       *path = NIL;
    const char *name;
    const char *ident;
    const char *type;
 
    Assert(MemoryContextIsValid(context));
 
    /*
     * Figure out the transient context_id of this context and each of its
     * ancestors.
     */
    for (MemoryContext cur = context; cur != NULL; cur = cur->parent)
    {
        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, NULL, &stat, true);
 
    memset(values, 0, sizeof(values));
    memset(nulls, 0, sizeof(nulls));
 
    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;
    }
 
    if (name)
        values[0] = CStringGetTextDatum(name);
    else
        nulls[0] = true;
 
    if (ident)
    {
        int         idlen = strlen(ident);
        char        clipped_ident[MEMORY_CONTEXT_IDENT_DISPLAY_SIZE];
 
        /*
         * Some identifiers such as SQL query string can be very long,
         * truncate oversize identifiers.
         */
        if (idlen >= MEMORY_CONTEXT_IDENT_DISPLAY_SIZE)
            idlen = pg_mbcliplen(ident, idlen, MEMORY_CONTEXT_IDENT_DISPLAY_SIZE - 1);
 
        memcpy(clipped_ident, ident, idlen);
        clipped_ident[idlen] = '\0';
        values[1] = CStringGetTextDatum(clipped_ident);
    }
    else
        nulls[1] = true;
 
    switch (context->type)
    {
        case T_AllocSetContext:
            type = "AllocSet";
            break;
        case T_GenerationContext:
            type = "Generation";
            break;
        case T_SlabContext:
            type = "Slab";
            break;
        case T_BumpContext:
            type = "Bump";
            break;
        default:
            type = "???";
            break;
    }
 
    values[2] = CStringGetTextDatum(type);
    values[3] = Int32GetDatum(list_length(path));   /* level */
    values[4] = int_list_to_array(path);
    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);
    list_free(path);
}
 
/*
 * pg_get_backend_memory_contexts
 *      SQL SRF showing backend memory context.
 */
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);
 
    /*
     * 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;
}
 
/*
 * pg_log_backend_memory_contexts
 *      Signal a backend or an auxiliary process to log its memory contexts.
 *
 * By default, only superusers are allowed to signal to log the memory
 * contexts because allowing any users to issue this request at an unbounded
 * rate would cause lots of log messages and which can lead to denial of
 * service. Additional roles can be permitted with GRANT.
 *
 * On receipt of this signal, a backend or an auxiliary process sets the flag
 * in the signal handler, which causes the next CHECK_FOR_INTERRUPTS()
 * or process-specific interrupt handler to log the memory contexts.
 */
Datum
pg_log_backend_memory_contexts(PG_FUNCTION_ARGS)
{
    int         pid = PG_GETARG_INT32(0);
    PGPROC     *proc;
    ProcNumber  procNumber = INVALID_PROC_NUMBER;
 
    /*
     * See if the process with given pid is a backend or an auxiliary process.
     */
    proc = BackendPidGetProc(pid);
    if (proc == NULL)
        proc = AuxiliaryPidGetProc(pid);
 
    /*
     * BackendPidGetProc() and AuxiliaryPidGetProc() return NULL if the pid
     * isn't valid; but by the time we reach kill(), a process for which we
     * get a valid proc here might have terminated on its own.  There's no way
     * to acquire a lock on an arbitrary process to prevent that. But since
     * this mechanism is usually used to debug a backend or an auxiliary
     * process running and consuming lots of memory, that it might end on its
     * own first and its memory contexts are not logged is not a problem.
     */
    if (proc == NULL)
    {
        /*
         * This is just a warning so a loop-through-resultset will not abort
         * if one backend terminated on its own during the run.
         */
        ereport(WARNING,
                (errmsg("PID %d is not a PostgreSQL server process", pid)));
        PG_RETURN_BOOL(false);
    }
 
    procNumber = GetNumberFromPGProc(proc);
    if (SendProcSignal(pid, PROCSIG_LOG_MEMORY_CONTEXT, procNumber) < 0)
    {
        /* Again, just a warning to allow loops */
        ereport(WARNING,
                (errmsg("could not send signal to process %d: %m", pid)));
        PG_RETURN_BOOL(false);
    }
 
    PG_RETURN_BOOL(true);
}