has to recopy the input plan node's targetlist if it removes a
SubqueryScan node just below the non-projecting node. For simplicity
I made it recopy always. Per bug report from Allan Wang and Michael Fuhr.
< cmin/cmax pair and is stored in local memory.
> cmin/cmax pair and is stored in local memory. Another idea is to
> store both cmin and cmax only in local memory.
< have its heap and index files truncated. One issue is
< that no other backend should be able to add to the table
< at the same time, which is something that is currently
< allowed.
> removed or have its heap and index files truncated. One
> issue is that no other backend should be able to add to
> the table at the same time, which is something that is
> currently allowed.
> o Allow COPY on a newly-created table to skip WAL logging
450a452,456
> On crash recovery, the table involved in the COPY would
> have its heap and index files truncated. One issue is
> that no other backend should be able to add to the table
> at the same time, which is something that is currently
> allowed.
> * Use UTF8 encoding for NLS messages so all server encodings can
> read them properly
< o %Add support for Unicode
<
< To fix this, the data needs to be converted to/from UTF16/UTF8
< so the Win32 wcscoll() can be used, and perhaps other functions
< like towupper(). However, UTF8 already works with normal
< locales but provides no ordering or character set classes.
< could only see committed rows from another transaction. However,
> could only see rows from another completed transaction. However,
981c981
< proper visibility of the row, for example, for cursors.
> proper visibility of the row's cmin, for example, for cursors.
on a page, as suggested by ITAGAKI Takahiro. Also, change a few places
that were using some other estimates of max-items-per-page to consistently
use MaxOffsetNumber. This is conservatively large --- we could have used
the new MaxHeapTuplesPerPage macro, or a similar one for index tuples ---
but those places are simply declaring a fixed-size buffer and assuming it
will work, rather than actively testing for overrun. It seems safer to
size these buffers in a way that can't overflow even if the page is
corrupt.
* Merge xmin/xmax/cmin/cmax back into three header fields
Before subtransactions, there used to be only three fields needed to
store these four values. This was possible because only the current
transaction looks at the cmin/cmax values. If the current transaction
created and expired the row the fields stored where xmin (same as
xmax), cmin, cmax, and if the transaction was expiring a row from a
another transaction, the fields stored were xmin (cmin was not
needed), xmax, and cmax. Such a system worked because a transaction
could only see committed rows from another transaction. However,
subtransactions can see rows from outer transactions, and once the
subtransaction completes, the outer transaction continues, requiring
the storage of all four fields. With subtransactions, an outer
transaction can create a row, a subtransaction expire it, and when the
subtransaction completes, the outer transaction still has to have
proper visibility of the row, for example, for cursors.
One possible solution is to create a phantom cid which represents a
cmin/cmax pair and is stored in local memory.
< * Maintain a map of recently-expired rows
<
< This allows vacuum to target specific pages for possible free space
< without requiring a sequential scan.
<
Update entry:
> One complexity is that index entries still have to be vacuumed, and
> doing this without an index scan (by using the heap values to find the
> index entry) might be slow and unreliable, especially for user-defined
> index functions.
saves nearly 700kB in the default shared memory segment size, which seems
worthwhile, and it is a feature that many users won't use anyway. Per
Heikki's argument, there is no point in a compromise value --- those who
are using 2PC at all will probably want it at least equal to max_connections.
But we can't set it to zero by default without breaking the prepared_xacts
regression test.
