Re: trying again to get incremental backup

On Tue, Nov 14, 2023 at 2:10 AM Robert Haas <robertmhaas@gmail.com> wrote:
>
> On Mon, Nov 13, 2023 at 11:25 AM Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > Great stuff you got here.  I'm doing a first pass trying to grok the
> > whole thing for more substantive comments, but in the meantime here are
> > some cosmetic ones.
>
> Thanks, thanks, and thanks.
>
> I've fixed some things that you mentioned in the attached version.
> Other comments below.

Here are some more comments based on what I have read so far, mostly
cosmetics comments.

1.
+ * summary file yet, then stoppng doesn't make any sense, and we
+ * should wait until the next stop point instead.

Typo /stoppng/stopping

2.
+ /* Close temporary file and shut down xlogreader. */
+ FileClose(io.file);
+

We have already freed the xlogreader so the second part of the comment
is not valid.

3.+ /*
+ * If a relation fork is truncated on disk, there is in point in
+ * tracking anything about block modifications beyond the truncation
+ * point.


Typo. /there is in point/ there is no point

4.
+/*
+ * Special handling for WAL recods with RM_XACT_ID.
+ */

/recods/records

5.

+ if (xact_info == XLOG_XACT_COMMIT ||
+ xact_info == XLOG_XACT_COMMIT_PREPARED)
+ {
+ xl_xact_commit *xlrec = (xl_xact_commit *) XLogRecGetData(xlogreader);
+ xl_xact_parsed_commit parsed;
+ int i;
+
+ ParseCommitRecord(XLogRecGetInfo(xlogreader), xlrec, &parsed);
+ for (i = 0; i < parsed.nrels; ++i)
+ {
+ ForkNumber forknum;
+
+ for (forknum = 0; forknum <= MAX_FORKNUM; ++forknum)
+ if (forknum != FSM_FORKNUM)
+ BlockRefTableSetLimitBlock(brtab, &parsed.xlocators[i],
+    forknum, 0);
+ }
+ }

For SmgrCreate and Truncate I understand setting the 'limit block' but
why for commit/abort?  I think it would be better to add some comments
here.

6.
+ * Caller must set private_data->tli to the TLI of interest,
+ * private_data->read_upto to the lowest LSN that is not known to be safe
+ * to read on that timeline, and private_data->historic to true if and only
+ * if the timeline is not the current timeline. This function will update
+ * private_data->read_upto and private_data->historic if more WAL appears
+ * on the current timeline or if the current timeline becomes historic.
+ */
+static int
+summarizer_read_local_xlog_page(XLogReaderState *state,
+ XLogRecPtr targetPagePtr, int reqLen,
+ XLogRecPtr targetRecPtr, char *cur_page)

The comments say "private_data->read_upto to the lowest LSN that is
not known to be safe" but is it really the lowest LSN? I think it is
the highest LSN this is known to be safe for that TLI no?

7.
+ /* If it's time to remove any old WAL summaries, do that now. */
+ MaybeRemoveOldWalSummaries();

I was just wondering whether removing old summaries should be the job
of the wal summarizer or it should be the job of the checkpointer, I
mean while removing the old wals it can also check and remove the old
summaries?  Anyway, it's just a question and I do not have a strong
opinion on this.

8.
+ /*
+ * Whether we we removed the file or not, we need not consider it
+ * again.
+ */

Typo /Whether we we removed/ Whether we removed

9.
+/*
+ * Get an entry from a block reference table.
+ *
+ * If the entry does not exist, this function returns NULL. Otherwise, it
+ * returns the entry and sets *limit_block to the value from the entry.
+ */
+BlockRefTableEntry *
+BlockRefTableGetEntry(BlockRefTable *brtab, const RelFileLocator *rlocator,
+   ForkNumber forknum, BlockNumber *limit_block)

If this function is already returning 'BlockRefTableEntry' then why
would it need to set an extra '*limit_block' out parameter which it is
actually reading from the entry itself?


--
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com