It is possible that even if the primary waits for the subscriber to catch
up and then disables the subscription, the XLOG_RUNNING_XACTS record gets
inserted between the two steps by bgwriter and walsender processes it.
This can move the restart_lsn of the corresponding slot in an
unpredictable way which further leads to slot sync failure.
To ensure predictable behaviour, we drop the subscription and manually
create the slot before the test. The other idea we discussed to write a
predictable test is to use injection points to control the bgwriter
logging XLOG_RUNNING_XACTS but that needs more analysis. We can add a
separate test using injection points.
Per buildfarm
Author: Hou Zhijie
Reviewed-by: Amit Kapila, Shveta Malik
Discussion: https://postgr.es/m/CAA4eK1JD8h_XLRsK_o_Xh=5MhTzm+6d4Cb4_uPgFJ2wSQDah=g@mail.gmail.com
A NESTED path allows to extract data from nested levels of JSON
objects given by the parent path expression, which are projected as
columns specified using a nested COLUMNS clause, just like the parent
COLUMNS clause. Rows comprised from a NESTED columns are "joined"
to the row comprised from the parent columns. If a particular NESTED
path evaluates to 0 rows, then the nested COLUMNS will emit NULLs,
making it an OUTER join.
NESTED columns themselves may include NESTED paths to allow
extracting data from arbitrary nesting levels, which are likewise
joined against the rows at the parent level.
Multiple NESTED paths at a given level are called "sibling" paths
and their rows are combined by UNIONing them, that is, after being
joined against the parent row as described above.
Author: Nikita Glukhov <n.gluhov@postgrespro.ru>
Author: Teodor Sigaev <teodor@sigaev.ru>
Author: Oleg Bartunov <obartunov@gmail.com>
Author: Alexander Korotkov <aekorotkov@gmail.com>
Author: Andrew Dunstan <andrew@dunslane.net>
Author: Amit Langote <amitlangote09@gmail.com>
Author: Jian He <jian.universality@gmail.com>
Reviewers have included (in no particular order):
Andres Freund, Alexander Korotkov, Pavel Stehule, Andrew Alsup,
Erik Rijkers, Zihong Yu, Himanshu Upadhyaya, Daniel Gustafsson,
Justin Pryzby, Álvaro Herrera, Jian He
Discussion: https://postgr.es/m/cd0bb935-0158-78a7-08b5-904886deac4b@postgrespro.ru
Discussion: https://postgr.es/m/20220616233130.rparivafipt6doj3@alap3.anarazel.de
Discussion: https://postgr.es/m/abd9b83b-aa66-f230-3d6d-734817f0995d%40postgresql.org
Discussion: https://postgr.es/m/CA+HiwqE4XTdfb1nW=Ojoy_tQSRhYt-q_kb6i5d4xcKyrLC1Nbg@mail.gmail.com
Currently, get_json_expr_options() does not emit the default values
for QUOTES (KEEP QUOTES) and WRAPPER (WITHOUT WRAPPER). That causes
the deparsed JSON_TABLE() columns, such as those contained in a a
view's query, to behave differently when executed than the original
definition. That's because the rules encoded in
transformJsonTableColumns() will choose either JSON_VALUE() or
JSON_QUERY() as implementation to execute a given column's path
expression depending on the QUOTES and WRAPPER specificationd and
they have slightly different semantics.
Reported-by: Jian He <jian.universality@gmail.com>
Discussion: https://postgr.es/m/CACJufxEqhqsfrg_p7EMyo5zak3d767iFDL8vz_4%3DZBHpOtrghw%40mail.gmail.com
Currently, transformJsonFuncExpr() enforces some restrictions on
the combinations of QUOTES and WRAPPER clauses that can be specified
in JSON_QUERY(). The intent was to only prevent the useless
combination WITH WRAPPER OMIT QUOTES, but the coding prevented KEEP
QUOTES too, which is not helpful. Fix that.
When testing buffer pool logic, it is useful to be able to evict
arbitrary blocks. This function can be used in SQL queries over the
pg_buffercache view to set up a wide range of buffer pool states. Of
course, buffer mappings might change concurrently so you might evict a
block other than the one you had in mind, and another session might
bring it back in at any time. That's OK for the intended purpose of
setting up developer testing scenarios, and more complicated interlocking
schemes to give stronger guararantees about that would likely be less
flexible for actual testing work anyway. Superuser-only.
Author: Palak Chaturvedi <chaturvedipalak1911@gmail.com>
Author: Thomas Munro <thomas.munro@gmail.com> (docs, small tweaks)
Reviewed-by: Nitin Jadhav <nitinjadhavpostgres@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Cary Huang <cary.huang@highgo.ca>
Reviewed-by: Cédric Villemain <cedric.villemain+pgsql@abcsql.com>
Reviewed-by: Jim Nasby <jim.nasby@gmail.com>
Reviewed-by: Maxim Orlov <orlovmg@gmail.com>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: https://postgr.es/m/CALfch19pW48ZwWzUoRSpsaV9hqt0UPyaBPC4bOZ4W+c7FF566A@mail.gmail.com
This adds tab completion of "GRANT" and "REVOKE [GRANT OPTION FOR]"
for ALTER DEFAULT PRIVILEGES, and adds "WITH GRANT OPTION" for
ALTER DEFAULT PRIVILEGES ... GRANT ... TO role.
Author: Vignesh C, with cosmetic adjustments by me
Reviewed-by: Shubham Khanna, Masahiko Sawada
Discussion: https://postgr.es/m/CALDaNm1aEdJb-QJi%3DGWStkfj_%2BEDUK_VtDkn%2BTjQ2z7HyU0MBw%40mail.gmail.com
One of the assertions was the subject of a false positive complaint from
Coverity, but none of the assertions added much, so get rid of them.
Reported-By: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/3000247.1712537309@sss.pgh.pa.us
While SH_STAT() is only used for debugging, the allocated array can be large,
and therefore should be freed.
It's unclear why coverity started warning now.
Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Reported-by: Coverity
Discussion: https://postgr.es/m/3005248.1712538233@sss.pgh.pa.us
Backpatch: 12-
libpq now always tries to send ALPN. With the traditional negotiated
SSL connections, the server accepts the ALPN, and refuses the
connection if it's not what we expect, but connecting without ALPN is
still OK. With the new direct SSL connections, ALPN is mandatory.
NOTE: This uses "TBD-pgsql" as the protocol ID. We must register a
proper one with IANA before the release!
Author: Greg Stark, Heikki Linnakangas
Reviewed-by: Matthias van de Meent, Jacob Champion
By skipping SSLRequest, you can eliminate one round-trip when
establishing a TLS connection. It is also more friendly to generic TLS
proxies that don't understand the PostgreSQL protocol.
This is disabled by default in libpq, because the direct TLS handshake
will fail with old server versions. It can be enabled with the
sslnegotation=direct option. It will still fall back to the negotiated
TLS handshake if the server rejects the direct attempt, either because
it is an older version or the server doesn't support TLS at all, but
the fallback can be disabled with the sslnegotiation=requiredirect
option.
Author: Greg Stark, Heikki Linnakangas
Reviewed-by: Matthias van de Meent, Jacob Champion
This fixes the few corner cases noted in commit 705843d294, as shown
by the changes in the test.
Author: Heikki Linnakangas, Matthias van de Meent
Reviewed-by: Jacob Champion
The ANALYZE command prefetches and reads sample blocks chosen by a
BlockSampler algorithm. Instead of calling [Prefetch|Read]Buffer() for
each block, ANALYZE now uses the streaming API introduced in b5a9b18cd0.
Author: Nazir Bilal Yavuz <byavuz81@gmail.com>
Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Jakub Wartak <jakub.wartak@enterprisedb.com>
Reviewed-by: Heikki Linnakangas <hlinnaka@iki.fi>
Reviewed-by: Thomas Munro <thomas.munro@gmail.com>
Discussion: https://postgr.es/m/flat/CAN55FZ0UhXqk9v3y-zW_fp4-WCp43V8y0A72xPmLkOM%2B6M%2BmJg%40mail.gmail.com
This adds a new SQL function injection_points_set_local() that can be
used to force injection points to be run only in the process where they
are attached. This is handy for SQL tests to:
- Detach automatically injection points when the process exits.
- Allow tests with injection points to run concurrently with other test
suites, so as such modules do not have to be marked with
NO_INSTALLCHECK.
Currently, the only condition that can be registered is for a PID.
This could be extended to more kinds later, if required, like database
names/OIDs, roles, or more concepts I did not consider.
Using a single function for SQL scripts is an idea from Heikki
Linnakangas.
Reviewed-by: Andrey Borodin
Discussion: https://postgr.es/m/ZfP7IDs9TvrKe49x@paquier.xyz
The new "log_connection_negotiation" server option causes the server
to print messages to the log when it receives a SSLRequest or
GSSENCRequest packet from the client. Together with "log_connections",
it gives a trace of how a connection and encryption is
negotiatated. Use the option in the libpq_encryption test, to verify
in more detail how libpq negotiates encryption with different
gssencmode and sslmode options.
This revealed a couple of cases where libpq retries encryption or
authentication, when it should already know that it cannot succeed. I
marked them with XXX comments in the test tables. They only happen
when the connection was going to fail anyway, and only with rare
combinations of options, so they're not serious.
Discussion: https://www.postgresql.org/message-id/CAEze2Wja8VUoZygCepwUeiCrWa4jP316k0mvJrOW4PFmWP0Tcw@mail.gmail.com
Previously, libpq would establish the TCP connection, and then
immediately disconnect if the credentials were not available. The
same thing happened if you tried to use a Unix domain socket with
gssencmode=require. Check those conditions before establishing the TCP
connection.
This is a very minor issue, but my motivation to do this now is that
I'm about to add more detail to the tests for encryption negotiation.
This makes the case of gssencmode=require but no credentials
configured fail at the same stage as with gssencmode=require and
GSSAPI support not compiled at all. That avoids having to deal with
variations in expected output depending on build options.
Discussion: https://www.postgresql.org/message-id/CAEze2Wja8VUoZygCepwUeiCrWa4jP316k0mvJrOW4PFmWP0Tcw@mail.gmail.com
Test all combinations of gssencmode, sslmode, whether the server
supports SSL and/or GSSAPI encryption, and whether they are accepted
by pg_hba.conf. This is in preparation for refactoring that code in
libpq, and for adding a new option for "direct SSL" connections, which
adds another dimension to the logic.
If we add even more options in the future, testing all combinations
will become unwieldy and we'll need to rethink this, but for now an
exhaustive test is nice.
Author: Heikki Linnakangas, Matthias van de Meent
Reviewed-by: Jacob Champion
Discussion: https://www.postgresql.org/message-id/a3af4070-3556-461d-aec8-a8d794f94894@iki.fi
As written, the test would fail when run repeatedly because one of the
injection points attached was not detached. This would not matter if
the test is rewritten to be concurrently safe, but let's be clean and
it is a good practice.
Oversight in 6a1ea02c49.
Discussion: https://postgr.es/m/ZfP7IDs9TvrKe49x@paquier.xyz
Replace (expr op C1) OR (expr op C2) ... with expr op ANY(ARRAY[C1, C2, ...])
on the preliminary stage of optimization when we are still working with the
expression tree.
Here Cn is a n-th constant expression, 'expr' is non-constant expression, 'op'
is an operator which returns boolean result and has a commuter (for the case
of reverse order of constant and non-constant parts of the expression,
like 'Cn op expr').
Sometimes it can lead to not optimal plan. This is why there is a
or_to_any_transform_limit GUC. It specifies a threshold value of length of
arguments in an OR expression that triggers the OR-to-ANY transformation.
Generally, more groupable OR arguments mean that transformation will be more
likely to win than to lose.
Discussion: https://postgr.es/m/567ED6CA.2040504%40sigaev.ru
Author: Alena Rybakina <lena.ribackina@yandex.ru>
Author: Andrey Lepikhov <a.lepikhov@postgrespro.ru>
Reviewed-by: Peter Geoghegan <pg@bowt.ie>
Reviewed-by: Ranier Vilela <ranier.vf@gmail.com>
Reviewed-by: Alexander Korotkov <aekorotkov@gmail.com>
Reviewed-by: Robert Haas <robertmhaas@gmail.com>
Reviewed-by: Jian He <jian.universality@gmail.com>
When restarting the cluster fails the code introduced in 33774978c7
printed the full log contents to aid debugging. For cases when the
logfile is large this adds unnecessary overhead. Reduce to printing
the logfile path instead.
Reported-by: Andres Freund <andres@anarazel.de>
Discussion: https://postgr.es/m/20240406214439.2n4zf2w7ukhf7dsy@awork3.anarazel.de
What the documentation calls an exclude_element is an index_elem
according to gram.y, and it allows all the same options that
a CREATE INDEX column specification does. The COLLATE patch
neglected to update the CREATE/ALTER TABLE docs about that,
and later the opclass-parameters patch made the same oversight.
Add those options to the syntax synopses, and polish the
associated text a bit.
Back-patch to v13 where opclass parameters came in. We could
update v12 with just the COLLATE omission, but it doesn't quite
seem worth the trouble at this point.
Shihao Zhong, reviewed by Daniel Vérité, Shubham Khanna and myself
Discussion: https://postgr.es/m/CAGRkXqShbVyB8E3gapfdtuwiWTiK=Q67Qb9qwxu=+-w0w46EBA@mail.gmail.com
In one multixact.c edge case, we need a mechanism to wait for one
multixact offset to be written before being allowed to read the next
one. We used to handle this case by sleeping for one millisecond and
retrying, but such sleeps have been reported as problematic in
production cases. We can avoid the problem by using a condition
variable: readers sleep on it and then every creator of multixacts
broadcasts into the CV when creation is sufficiently far along.
Author: Kyotaro Horiguchi <horikyotajntt@gmail.com>
Reviewed-by: Andrey Borodin <amborodin@acm.org>
Discussion: https://postgr.es/m/47A598F4-B4E7-4029-8FEC-A06A6C3CB4B5@yandex-team.ru
Discussion: https://postgr.es/m/20200515.090333.24867479329066911.horikyota.ntt
nbtree index scans with SAOP inequalities (but no SAOP equalities)
performed extra ORDER proc lookups for any remaining equality strategy
scan keys. This could waste cycles, and caused assertion failures.
Keeping around a separate ORDER proc is only necessary for a scan's
non-array/non-SAOP equality scan keys when the scan has at least one
other SAOP equality strategy key (a SAOP inequality shouldn't count).
To fix, replace _bt_preprocess_array_keys_final's assertion with a test
that makes the function return early when the scan has no SAOP equality
scan keys.
Oversight in commit 1b134ca5, which enhanced nbtree ScalarArrayOp
execution.
Reported-By: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/0539d3d3-a402-0a49-ed5e-26429dffc4bd@gmail.com
If the OpenLDAP installation directory is not found, set $setup to 0
so that the LDAP tests are skipped. The macOS checks were already
doing that, but the checks on other OS's were not. While we're at it,
improve the error message when the tests are skipped, to specify
whether the OS is supported at all, or if we just didn't find the
installation directory.
This was accidentally "working" without this, i.e. we were skipping
the tests if the OpenLDAP installation was not found, because of a bug
in the LdapServer test module: the END block clobbered the exit code
so if the script die()s before running the first subtest, the whole
test script was marked as SKIPped. The next commit will fix that bug,
but we need to fix the setup code first.
These checks should probably go into configure/meson, but this is
better than nothing and allows fixing the bug in the END block.
Backpatch to all supported versions.
Discussion: https://www.postgresql.org/message-id/fb898a70-3a88-4629-88e9-f2375020061d@iki.fi
29f6a959c added a bump allocator type for efficient compact allocations.
Here we make use of this for non-bounded tuplesorts to store tuples.
This is very space efficient when storing narrow tuples due to bump.c
not having chunk headers. This means we can fit more tuples in work_mem
before spilling to disk, or perform an in-memory sort touching fewer
cacheline.
Author: David Rowley
Reviewed-by: Nathan Bossart
Reviewed-by: Matthias van de Meent
Reviewed-by: Tomas Vondra
Reviewed-by: John Naylor
Discussion: https://postgr.es/m/CAApHDvqGSpCU95TmM=Bp=6xjL_nLys4zdZOpfNyWBk97Xrdj2w@mail.gmail.com
This tracks the position of WAL that's been fully copied into WAL
buffers by all processes emitting WAL. (For some reason we call that
"WAL insertion"). This is updated using atomic monotonic advance during
WaitXLogInsertionsToFinish, which is not when the insertions actually
occur, but it's the only place where we know where have all the
insertions have completed.
This value is useful in WALReadFromBuffers, which can verify that
callers don't try to read past what has been inserted. (However, more
infrastructure is needed in order to actually use WAL after the flush
point, since it could be lost.)
The value is also useful in WaitXLogInsertionsToFinish() itself, since
we can now exit quickly when all WAL has been already inserted, without
even having to take any locks.
This introduces a bump MemoryContext type. The bump context is best
suited for short-lived memory contexts which require only allocations
of memory and never a pfree or repalloc, which are unsupported.
Memory palloc'd into a bump context has no chunk header. This makes
bump a useful context type when lots of small allocations need to be
done without any need to pfree those allocations. Allocation sizes are
rounded up to the next MAXALIGN boundary, so with this and no chunk
header, allocations are very compact indeed.
Allocations are also very fast as bump does not check any freelists to
try and make use of previously free'd chunks. It just checks if there
is enough room on the current block, and if so it bumps the freeptr
beyond this chunk and returns the value that the freeptr was previously
pointing to. Simple and fast. A new block is malloc'd when there's not
enough space in the current block.
Code using the bump allocator must take care never to call any functions
which could try to call realloc() (or variants), pfree(),
GetMemoryChunkContext() or GetMemoryChunkSpace() on a bump allocated
chunk. Due to lack of chunk headers, these operations are unsupported.
To increase the chances of catching such issues, when compiled with
MEMORY_CONTEXT_CHECKING, bump allocated chunks are given a header and
any attempt to perform an unsupported operation will result in an ERROR.
Without MEMORY_CONTEXT_CHECKING, code attempting an unsupported
operation could result in a segfault.
A follow-on commit will implement the first user of bump.
Author: David Rowley
Reviewed-by: Nathan Bossart
Reviewed-by: Matthias van de Meent
Reviewed-by: Tomas Vondra
Reviewed-by: John Naylor
Discussion: https://postgr.es/m/CAApHDvqGSpCU95TmM=Bp=6xjL_nLys4zdZOpfNyWBk97Xrdj2w@mail.gmail.com
Reserve 4 bits for MemoryContextMethodID rather than 3. 3 bits did
technically allow a maximum of 8 memory context types, however, we've
opted to reserve some bit patterns which left us with only 4 slots, all
of which were used.
Here we add another bit which frees up 8 slots for future memory context
types.
In passing, adjust the enum names in MemoryContextMethodID to make it
more clear which ones can be used and which ones are reserved.
Author: Matthias van de Meent, David Rowley
Discussion: https://postgr.es/m/CAApHDvqGSpCU95TmM=Bp=6xjL_nLys4zdZOpfNyWBk97Xrdj2w@mail.gmail.com
Until now, when calling pq_putmessage to write new data to a libpq
socket, all writes are copied into a buffer and that buffer gets flushed
when full to avoid having to perform small writes to the socket.
There are cases where we must write large amounts of data to the socket,
sometimes larger than the size of the buffer. In this case, it's
wasteful to memcpy this data into the buffer and flush it out, instead,
we can send it directly from the memory location that the data is already
stored in.
Here we adjust internal_putbytes() so that after having just flushed the
buffer to the socket, if the remaining bytes to send is as big or bigger
than the buffer size, we just send directly rather than needlessly
copying into the PqSendBuffer buffer first.
Examples of operations that write large amounts of data in one message
are; outputting large tuples with SELECT or COPY TO STDOUT and
pg_basebackup.
Author: Melih Mutlu
Reviewed-by: Heikki Linnakangas
Reviewed-by: Jelte Fennema-Nio
Reviewed-by: David Rowley
Reviewed-by: Ranier Vilela
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/CAGPVpCR15nosj0f6xe-c2h477zFR88q12e6WjEoEZc8ZYkTh3Q@mail.gmail.com
Until now, heapgetpage()'s loop over all tuples performed some conditional
checks for each tuple, even though condition did not change across the loop.
This commit fixes that by moving the loop into an inline function. By calling
it with different constant arguments, the compiler can generate an optimized
loop for the different conditions, at the price of two per-page checks.
For cases of all-visible tables and an isolation level other than
serializable, speedups of up to 25% have been measured.
Reviewed-by: John Naylor <johncnaylorls@gmail.com>
Reviewed-by: Zhang Mingli <zmlpostgres@gmail.com>
Tested-by: Quan Zongliang <quanzongliang@yeah.net>
Discussion: https://postgr.es/m/20230716015656.xjvemfbp5fysjiea@awork3.anarazel.de
Discussion: https://postgr.es/m/2ef7ff1b-3d18-2283-61b1-bbd25fc6c7ce@yeah.net
Commit 792752af4e added infrastructure for using AVX-512 intrinsic
functions, and this commit uses that infrastructure to optimize
visibilitymap_count(). Specificially, a new pg_popcount_masked()
function is introduced that applies a bitmask to every byte in the
buffer prior to calculating the population count, which is used to
filter out the all-visible or all-frozen bits as needed. Platforms
without AVX-512 support should also see a nice speedup due to the
reduced number of calls to a function pointer.
Co-authored-by: Ants Aasma
Discussion: https://postgr.es/m/BL1PR11MB5304097DF7EA81D04C33F3D1DCA6A%40BL1PR11MB5304.namprd11.prod.outlook.com
Presently, pg_popcount() processes data in 32-bit or 64-bit chunks
when possible. Newer hardware that supports AVX-512 instructions
can use 512-bit chunks, which provides a nice speedup, especially
for larger buffers. This commit introduces the infrastructure
required to detect compiler and CPU support for the required
AVX-512 intrinsic functions, and it adds a new pg_popcount()
implementation that uses these functions. If CPU support for this
optimized implementation is detected at runtime, a function pointer
is updated so that it is used by subsequent calls to pg_popcount().
Most of the existing in-tree calls to pg_popcount() should benefit
from these instructions, and calls with smaller buffers should at
least not regress compared to v16. The new infrastructure
introduced by this commit can also be used to optimize
visibilitymap_count(), but that is left for a follow-up commit.
Co-authored-by: Paul Amonson, Ants Aasma
Reviewed-by: Matthias van de Meent, Tom Lane, Noah Misch, Akash Shankaran, Alvaro Herrera, Andres Freund, David Rowley
Discussion: https://postgr.es/m/BL1PR11MB5304097DF7EA81D04C33F3D1DCA6A%40BL1PR11MB5304.namprd11.prod.outlook.com
When we determine that a wanted block can't be combined with the current
pending read, it's time to start that read to get it out of the way. An
"if" in that code path should have been a "while", because it might take
more than one go in case of partial reads. This was only broken for
smaller ranges, as the more common case of io_combine_limit-sized ranges
is handled earlier in the code and knows how to loop, hiding the bug for
a while.
Discovered while testing large parallel sequential scans of partially
cached tables. The ramp-up-and-down block allocator for parallel scans
could hit the problem case and skip some blocks near the end that should
have been streamed.
Defect in commit b5a9b18c.
Discussion: https://postgr.es/m/CA%2BhUKG%2Bh8Whpv0YsJqjMVkjYX%2B80fTVc6oi-V%2BzxJvykLpLHYQ%40mail.gmail.com
The buildfarm members using debug_parallel_query = regress are mostly
unhappy with this test. I guess what is happening is that rows
generated by a parallel worker are buffered, and might or might not
get to the leader before the expected error occurs. We did not see
any variability in the old version of this test because each FETCH
would succeed or fail atomically, leading to a predictable number of
rows emitted before failure. I don't find this to be a bug, just
unspecified behavior, so let's disable parallel query for this one
test case to make the results stable.
Formerly this was done with a cursor, which is problematic since
not all result-set-returning query types can be put into a cursor.
The new implementation is better integrated into other psql
features, too.
Daniel Vérité, reviewed by Laurenz Albe and myself (and whacked
around a bit by me, so any remaining bugs are my fault)
Discussion: https://postgr.es/m/CAKZiRmxsVTkO928CM+-ADvsMyePmU3L9DQCa9NwqjvLPcEe5QA@mail.gmail.com
This patch generalizes libpq's existing single-row mode to allow
individual partial-result PGresults to contain up to N rows, rather
than always one row. This reduces malloc overhead compared to plain
single-row mode, and it is very useful for psql's FETCH_COUNT feature,
since otherwise we'd have to add code (and cycles) to either merge
single-row PGresults into a bigger one or teach psql's
results-printing logic to accept arrays of PGresults.
To avoid API breakage, PQsetSingleRowMode() remains the same, and we
add a new function PQsetChunkedRowsMode() to invoke the more general
case. Also, PGresults obtained the old way continue to carry the
PGRES_SINGLE_TUPLE status code, while if PQsetChunkedRowsMode() is
used then their status code is PGRES_TUPLES_CHUNK. The underlying
logic is the same either way, though.
Daniel Vérité, reviewed by Laurenz Albe and myself (and whacked
around a bit by me, so any remaining bugs are my fault)
Discussion: https://postgr.es/m/CAKZiRmxsVTkO928CM+-ADvsMyePmU3L9DQCa9NwqjvLPcEe5QA@mail.gmail.com
Amit Kapila