On Tue, Jul 5, 2022 at 8:00 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> On Mon, Jul 4, 2022 at 6:12 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > On Mon, May 30, 2022 at 11:13 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
> > >
> > > I've attached three POC patches:
> > >
> >
> > I think it will be a good idea if you can add a short commit message
> > at least to say which patch is proposed for HEAD and which one is for
> > back branches. Also, it would be good if you can add some description
> > of the fix in the commit message. Let's remove poc* from the patch
> > name.
> >
> > Review poc_add_running_catchanges_xacts_to_serialized_snapshot
> > =====================================================
>
> Few more comments:
Thank you for the comments.
> 1.
> +
> + /* This array must be sorted in xidComparator order */
> + TransactionId *xip;
> + } catchanges;
> };
>
> This array contains the transaction ids for subtransactions as well. I
> think it is better mention the same in comments.
Updated.
>
> 2. Are we anytime removing transaction ids from catchanges->xip array?
No.
> If not, is there a reason for the same? I think we can remove it
> either at commit/abort or even immediately after adding the xid/subxid
> to committed->xip array.
It might be a good idea but I'm concerned that removing XID from the
array at every commit/abort or after adding it to committed->xip array
might be costly as it requires adjustment of the array to keep its
order. Removing XIDs from the array would make bsearch faster but the
array is updated reasonably often (every 15 sec).
>
> 3.
> + if (readBytes != sz)
> + {
> + int save_errno = errno;
> +
> + CloseTransientFile(fd);
> +
> + if (readBytes < 0)
> + {
> + errno = save_errno;
> + ereport(ERROR,
> + (errcode_for_file_access(),
> + errmsg("could not read file \"%s\": %m", path)));
> + }
> + else
> + ereport(ERROR,
> + (errcode(ERRCODE_DATA_CORRUPTED),
> + errmsg("could not read file \"%s\": read %d of %zu",
> + path, readBytes, sz)));
> + }
>
> This is the fourth instance of similar error handling code in
> SnapBuildRestore(). Isn't it better to extract this into a separate
> function?
Good idea, updated.
>
> 4.
> +TransactionId *
> +ReorderBufferGetCatalogChangesXacts(ReorderBuffer *rb, size_t *xcnt_p)
> +{
> + HASH_SEQ_STATUS hash_seq;
> + ReorderBufferTXNByIdEnt *ent;
> + TransactionId *xids;
> + size_t xcnt = 0;
> + size_t xcnt_space = 64; /* arbitrary number */
> +
> + xids = (TransactionId *) palloc(sizeof(TransactionId) * xcnt_space);
> +
> + hash_seq_init(&hash_seq, rb->by_txn);
> + while ((ent = hash_seq_search(&hash_seq)) != NULL)
> + {
> + ReorderBufferTXN *txn = ent->txn;
> +
> + if (!rbtxn_has_catalog_changes(txn))
> + continue;
>
> It would be better to allocate memory the first time we have to store
> xids. There is a good chance that many a time this function will do
> just palloc without having to store any xid.
Agreed.
>
> 5. Do you think we should do some performance testing for a mix of
> ddl/dml workload to see if it adds any overhead in decoding due to
> serialize/restore doing additional work? I don't think it should add
> some meaningful overhead but OTOH there is no harm in doing some
> testing of the same.
Yes, it would be worth trying. I also believe this change doesn't
introduce noticeable overhead but let's check just in case.
I've attached an updated patch.
Regards,
--
Masahiko Sawada
EDB: https://www.enterprisedb.com/