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/*-------------------------------------------------------------------------
*
* aio_funcs.c
* AIO - SQL interface for AIO
*
*
* Portions Copyright (c) 1996-2025, PostgreSQL Global Development Group
* Portions Copyright (c) 1994, Regents of the University of California
*
* IDENTIFICATION
* src/backend/storage/aio/aio_funcs.c
*
*-------------------------------------------------------------------------
*/
#include "postgres.h"
#include "fmgr.h"
#include "funcapi.h"
#include "nodes/execnodes.h"
#include "port/atomics.h"
#include "storage/aio_internal.h"
#include "storage/lock.h"
#include "storage/proc.h"
#include "storage/procnumber.h"
#include "utils/builtins.h"
#include "utils/fmgrprotos.h"
#include "utils/tuplestore.h"
/*
* Byte length of an iovec.
*/
static size_t
iov_byte_length(const struct iovec *iov, int cnt)
{
size_t len = 0;
for (int i = 0; i < cnt; i++)
{
len += iov[i].iov_len;
}
return len;
}
Datum
pg_get_aios(PG_FUNCTION_ARGS)
{
ReturnSetInfo *rsinfo = (ReturnSetInfo *) fcinfo->resultinfo;
InitMaterializedSRF(fcinfo, 0);
#define PG_GET_AIOS_COLS 15
for (uint64 i = 0; i < pgaio_ctl->io_handle_count; i++)
{
PgAioHandle *live_ioh = &pgaio_ctl->io_handles[i];
uint32 ioh_id = pgaio_io_get_id(live_ioh);
Datum values[PG_GET_AIOS_COLS] = {0};
bool nulls[PG_GET_AIOS_COLS] = {0};
ProcNumber owner;
PGPROC *owner_proc;
int32 owner_pid;
PgAioHandleState start_state;
uint64 start_generation;
PgAioHandle ioh_copy;
struct iovec iov_copy[PG_IOV_MAX];
/*
* There is no lock that could prevent the state of the IO to advance
* concurrently - and we don't want to introduce one, as that would
* introduce atomics into a very common path. Instead we
*
* 1) Determine the state + generation of the IO.
*
* 2) Copy the IO to local memory.
*
* 3) Check if state or generation of the IO changed. If the state
* changed, retry, if the generation changed don't display the IO.
*/
/* 1) from above */
start_generation = live_ioh->generation;
/*
* Retry at this point, so we can accept changing states, but not
* changing generations.
*/
retry:
pg_read_barrier();
start_state = live_ioh->state;
if (start_state == PGAIO_HS_IDLE)
continue;
/* 2) from above */
memcpy(&ioh_copy, live_ioh, sizeof(PgAioHandle));
/*
* Safe to copy even if no iovec is used - we always reserve the
* required space.
*/
memcpy(&iov_copy, &pgaio_ctl->iovecs[ioh_copy.iovec_off],
PG_IOV_MAX * sizeof(struct iovec));
/*
* Copy information about owner before 3) below, if the process exited
* it'd have to wait for the IO to finish first, which we would detect
* in 3).
*/
owner = ioh_copy.owner_procno;
owner_proc = GetPGProcByNumber(owner);
owner_pid = owner_proc->pid;
/* 3) from above */
pg_read_barrier();
/*
* The IO completed and a new one was started with the same ID. Don't
* display it - it really started after this function was called.
* There be a risk of a livelock if we just retried endlessly, if IOs
* complete very quickly.
*/
if (live_ioh->generation != start_generation)
continue;
/*
* The IO's state changed while we were "rendering" it. Just start
* from scratch. There's no risk of a livelock here, as an IO has a
* limited sets of states it can be in, and state changes go only in a
* single direction.
*/
if (live_ioh->state != start_state)
goto retry;
/*
* Now that we have copied the IO into local memory and checked that
* it's still in the same state, we are not allowed to access "live"
* memory anymore. To make it slightly easier to catch such cases, set
* the "live" pointers to NULL.
*/
live_ioh = NULL;
owner_proc = NULL;
/* column: owning pid */
if (owner_pid != 0)
values[0] = Int32GetDatum(owner_pid);
else
nulls[0] = false;
/* column: IO's id */
values[1] = ioh_id;
/* column: IO's generation */
values[2] = Int64GetDatum(start_generation);
/* column: IO's state */
values[3] = CStringGetTextDatum(pgaio_io_get_state_name(&ioh_copy));
/*
* If the IO is in PGAIO_HS_HANDED_OUT state, none of the following
* fields are valid yet (or are in the process of being set).
* Therefore we don't want to display any other columns.
*/
if (start_state == PGAIO_HS_HANDED_OUT)
{
memset(nulls + 4, 1, (lengthof(nulls) - 4) * sizeof(bool));
goto display;
}
/* column: IO's operation */
values[4] = CStringGetTextDatum(pgaio_io_get_op_name(&ioh_copy));
/* columns: details about the IO's operation (offset, length) */
switch (ioh_copy.op)
{
case PGAIO_OP_INVALID:
nulls[5] = true;
nulls[6] = true;
break;
case PGAIO_OP_READV:
values[5] = Int64GetDatum(ioh_copy.op_data.read.offset);
values[6] =
Int64GetDatum(iov_byte_length(iov_copy, ioh_copy.op_data.read.iov_length));
break;
case PGAIO_OP_WRITEV:
values[5] = Int64GetDatum(ioh_copy.op_data.write.offset);
values[6] =
Int64GetDatum(iov_byte_length(iov_copy, ioh_copy.op_data.write.iov_length));
break;
}
/* column: IO's target */
values[7] = CStringGetTextDatum(pgaio_io_get_target_name(&ioh_copy));
/* column: length of IO's data array */
values[8] = Int16GetDatum(ioh_copy.handle_data_len);
/* column: raw result (i.e. some form of syscall return value) */
if (start_state == PGAIO_HS_COMPLETED_IO
|| start_state == PGAIO_HS_COMPLETED_SHARED
|| start_state == PGAIO_HS_COMPLETED_LOCAL)
values[9] = Int32GetDatum(ioh_copy.result);
else
nulls[9] = true;
/*
* column: result in the higher level representation (unknown if not
* finished)
*/
values[10] =
CStringGetTextDatum(pgaio_result_status_string(ioh_copy.distilled_result.status));
/* column: target description */
values[11] = CStringGetTextDatum(pgaio_io_get_target_description(&ioh_copy));
/* columns: one for each flag */
values[12] = BoolGetDatum(ioh_copy.flags & PGAIO_HF_SYNCHRONOUS);
values[13] = BoolGetDatum(ioh_copy.flags & PGAIO_HF_REFERENCES_LOCAL);
values[14] = BoolGetDatum(ioh_copy.flags & PGAIO_HF_BUFFERED);
display:
tuplestore_putvalues(rsinfo->setResult, rsinfo->setDesc, values, nulls);
}
return (Datum) 0;
}
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