mcxtfuncs.c

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/*-------------------------------------------------------------------------
 *
 * mcxtfuncs.c
 *    Functions to show backend memory context.
 *
 * Portions Copyright (c) 1996-2023, 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 "miscadmin.h"
#include "mb/pg_wchar.h"
#include "storage/proc.h"
#include "storage/procarray.h"
#include "utils/builtins.h"
 
/* ----------
 * The max bytes for showing identifiers of MemoryContext.
 * ----------
 */
#define MEMORY_CONTEXT_IDENT_DISPLAY_SIZE   1024
 
/*
 * PutMemoryContextsStatsTupleStore
 *      One recursion level for pg_get_backend_memory_contexts.
 */
static void
PutMemoryContextsStatsTupleStore(Tuplestorestate *tupstore,
                                 TupleDesc tupdesc, MemoryContext context,
                                 const char *parent, int level)
{
#define PG_GET_BACKEND_MEMORY_CONTEXTS_COLS 9
 
    Datum       values[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
    bool        nulls[PG_GET_BACKEND_MEMORY_CONTEXTS_COLS];
    MemoryContextCounters stat;
    MemoryContext child;
    const char *name;
    const char *ident;
 
    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().
     */
    if (ident && strcmp(name, "dynahash") == 0)
    {
        name = ident;
        ident = NULL;
    }
 
    /* Examine the context itself */
    memset(&stat, 0, sizeof(stat));
    (*context->methods->stats) (context, NULL, (void *) &level, &stat, true);
 
    memset(values, 0, sizeof(values));
    memset(nulls, 0, sizeof(nulls));
 
    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;
 
    if (parent)
        values[2] = CStringGetTextDatum(parent);
    else
        nulls[2] = true;
 
    values[3] = Int32GetDatum(level);
    values[4] = Int64GetDatum(stat.totalspace);
    values[5] = Int64GetDatum(stat.nblocks);
    values[6] = Int64GetDatum(stat.freespace);
    values[7] = Int64GetDatum(stat.freechunks);
    values[8] = Int64GetDatum(stat.totalspace - stat.freespace);
    tuplestore_putvalues(tupstore, tupdesc, values, nulls);
 
    for (child = context->firstchild; child != NULL; child = child->nextchild)
    {
        PutMemoryContextsStatsTupleStore(tupstore, tupdesc,
                                         child, name, level + 1);
    }
}
 
/*
 * 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;
 
    InitMaterializedSRF(fcinfo, 0);
    PutMemoryContextsStatsTupleStore(rsinfo->setResult, rsinfo->setDesc,
                                     TopMemoryContext, NULL, 0);
 
    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;
    BackendId   backendId = InvalidBackendId;
 
    proc = BackendPidGetProc(pid);
 
    /*
     * See if the process with given pid is a backend or an auxiliary process.
     *
     * If the given process is a backend, use its backend id in
     * SendProcSignal() later to speed up the operation. Otherwise, don't do
     * that because auxiliary processes (except the startup process) don't
     * have a valid backend id.
     */
    if (proc != NULL)
        backendId = proc->backendId;
    else
        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);
    }
 
    if (SendProcSignal(pid, PROCSIG_LOG_MEMORY_CONTEXT, backendId) < 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);
}