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Re: WIP: WAL prefetch (another approach)

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Dmitry Dolgov <9erthalion6@gmail.com>, David Steele <david@pgmasters.net>, Andres Freund <andres@anarazel.de>, Tomas Vondra <tomas.vondra@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2020-05-28T21:14:25Z
Lists: pgsql-hackers 
Thomas Munro escribió:

> @@ -1094,8 +1103,16 @@ WALRead(XLogReaderState *state,
>  			XLByteToSeg(recptr, nextSegNo, state->segcxt.ws_segsize);
>  			state->routine.segment_open(state, nextSegNo, &tli);
>  
> -			/* This shouldn't happen -- indicates a bug in segment_open */
> -			Assert(state->seg.ws_file >= 0);
> +			/* callback reported that there was no such file */
> +			if (state->seg.ws_file < 0)
> +			{
> +				errinfo->wre_errno = errno;
> +				errinfo->wre_req = 0;
> +				errinfo->wre_read = 0;
> +				errinfo->wre_off = startoff;
> +				errinfo->wre_seg = state->seg;
> +				return false;
> +			}

Ah, this is what Michael was saying ... we need to fix WALRead so that
it doesn't depend on segment_open alway returning a good FD.  This needs
a fix everywhere, not just here, and improve the error report interface.

Maybe it does make sense to get it fixed in pg13 and avoid a break
later.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Fix recovery_prefetch docs.

  2. Prefetch data referenced by the WAL, take II.

  3. Add circular WAL decoding buffer, take II.

  4. Fix generation of ./INSTALL for the distribution tarball

  5. Revert recovery prefetching feature.

  6. Sync guc.c and postgresql.conf.sample with the SGML docs.

  7. Add information of total data processed to replication slot stats.

  8. Doc: Review for "Optionally prefetch referenced data in recovery."

  9. Add circular WAL decoding buffer.

  10. Optionally prefetch referenced data in recovery.

  11. Remove read_page callback from XLogReader.

  12. Provide ReadRecentBuffer() to re-pin buffers by ID.

  13. Provide recovery_init_sync_method=syncfs.

  14. Mark factorial operator, and postfix operators in general, as deprecated.

  15. Rationalize GetWalRcv{Write,Flush}RecPtr().

  16. Support PrefetchBuffer() in recovery.

  17. Prevent hard failures of standbys caused by recycled WAL segments