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Commit08ccd56

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aio, bufmgr: Comment fixes/improvements
Some of these comments have been wrong for a while (12f3867), some Irecently introduced (da72269,55b454d). This includes an update to acomment in FlushBuffer(), which will be copied in a future commit.These changes seem big enough to be worth doing in separate commits.Suggested-by: Noah Misch <noah@leadboat.com>Discussion:https://postgr.es/m/20250319212530.80.nmisch@google.com
1 parent50cb750 commit08ccd56

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4 files changed

+27
-9
lines changed

4 files changed

+27
-9
lines changed

‎src/backend/postmaster/postmaster.c

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -4401,7 +4401,7 @@ maybe_adjust_io_workers(void)
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++io_worker_count;
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}
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else
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break;/*XXXtry againsoon? */
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break;/* try againnext time */
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}
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/* Too many running? */

‎src/backend/storage/buffer/bufmgr.c

Lines changed: 4 additions & 6 deletions
Original file line numberDiff line numberDiff line change
@@ -3929,9 +3929,10 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
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XLogFlush(recptr);
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/*
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* Now it's safe to write buffer to disk. Note that no one else should
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* have been able to write it while we were busy with log flushing because
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* only one process at a time can set the BM_IO_IN_PROGRESS bit.
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* Now it's safe to write the buffer to disk. Note that no one else should
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* have been able to write it, while we were busy with log flushing,
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* because we got the exclusive right to perform I/O by setting the
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* BM_IO_IN_PROGRESS bit.
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*/
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bufBlock=BufHdrGetBlock(buf);
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@@ -5499,9 +5500,6 @@ IsBufferCleanupOK(Buffer buffer)
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/*
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*Functions for buffer I/O handling
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*
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*Note: We assume that nested buffer I/O never occurs.
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*i.e at most one BM_IO_IN_PROGRESS bit is set per proc.
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*
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*Also note that these are used only for shared buffers, not local ones.
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*/
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‎src/include/storage/aio.h

Lines changed: 1 addition & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -80,7 +80,7 @@ typedef enum PgAioHandleFlags
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/*
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* The IO operations supported by the AIO subsystem.
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*
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* This could be in aio_internal.h, as it is notpubicly referenced, but
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* This could be in aio_internal.h, as it is notpublicly referenced, but
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* PgAioOpData currently *does* need to be public, therefore keeping this
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* public seems to make sense.
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*/

‎src/include/storage/aio_internal.h

Lines changed: 21 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -34,6 +34,11 @@
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* linearly through all states.
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*
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* State changes should all go through pgaio_io_update_state().
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*
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* Note that the externally visible functions to start IO
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* (e.g. FileStartReadV(), via pgaio_io_start_readv()) move an IO from
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* PGAIO_HS_HANDED_OUT to at least PGAIO_HS_STAGED and at most
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* PGAIO_HS_COMPLETED_LOCAL (at which point the handle will be reused).
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*/
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typedefenumPgAioHandleState
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{
@@ -285,6 +290,9 @@ typedef struct IoMethodOps
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/*
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* Start executing passed in IOs.
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*
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* Shall advance state to at least PGAIO_HS_SUBMITTED. (By the time this
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* returns, other backends might have advanced the state further.)
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*
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* Will not be called if ->needs_synchronous_execution() returned true.
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*
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* num_staged_ios is <= PGAIO_SUBMIT_BATCH_SIZE.
@@ -293,12 +301,24 @@ typedef struct IoMethodOps
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*/
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int(*submit) (uint16num_staged_ios,PgAioHandle**staged_ios);
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/*
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/* ---
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* Wait for the IO to complete. Optional.
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*
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* On return, state shall be on of
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* - PGAIO_HS_COMPLETED_IO
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* - PGAIO_HS_COMPLETED_SHARED
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* - PGAIO_HS_COMPLETED_LOCAL
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*
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* The callback must not block if the handle is already in one of those
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* states, or has been reused (see pgaio_io_was_recycled()). If, on
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* return, the state is PGAIO_HS_COMPLETED_IO, state will reach
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* PGAIO_HS_COMPLETED_SHARED without further intervention by the IO
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* method.
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*
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* If not provided, it needs to be guaranteed that the IO method calls
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* pgaio_io_process_completion() without further interaction by the
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* issuing backend.
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* ---
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*/
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void(*wait_one) (PgAioHandle*ioh,
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uint64ref_generation);

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