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* [PATCH v24 05/10] fixups.patch
@ 2021-02-10 21:56 Robert Haas <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Robert Haas @ 2021-02-10 21:56 UTC (permalink / raw)
---
doc/src/sgml/ddl.sgml | 3 ---
doc/src/sgml/ref/create_table.sgml | 15 +++++++++++----
src/backend/access/common/detoast.c | 5 ++---
src/backend/access/compression/compress_lz4.c | 10 +++++-----
src/backend/executor/nodeModifyTable.c | 2 +-
src/include/nodes/execnodes.h | 4 ++--
6 files changed, 21 insertions(+), 18 deletions(-)
diff --git a/doc/src/sgml/ddl.sgml b/doc/src/sgml/ddl.sgml
index 4d7ed698b9..1e9a4625cc 100644
--- a/doc/src/sgml/ddl.sgml
+++ b/doc/src/sgml/ddl.sgml
@@ -3762,9 +3762,6 @@ CREATE TABLE measurement (
<productname>PostgreSQL</productname>
tables (or, possibly, foreign tables). It is possible to specify a
tablespace and storage parameters for each partition separately.
- By default, each column in a partition inherits the compression method
- from parent table's column, however a different compression method can be
- set for each partition.
</para>
<para>
diff --git a/doc/src/sgml/ref/create_table.sgml b/doc/src/sgml/ref/create_table.sgml
index 51a7a977a5..a4b297340f 100644
--- a/doc/src/sgml/ref/create_table.sgml
+++ b/doc/src/sgml/ref/create_table.sgml
@@ -997,10 +997,17 @@ WITH ( MODULUS <replaceable class="parameter">numeric_literal</replaceable>, REM
<term><literal>COMPRESSION <replaceable class="parameter">compression_method</replaceable></literal></term>
<listitem>
<para>
- This sets the compression method for a column. The supported compression
- methods are <literal>pglz</literal> and <literal>lz4</literal>.
- <literal>lz4</literal> is available only if <literal>--with-lz4</literal>
- was used when building <productname>PostgreSQL</productname>. The default
+ The <literal>COMPRESSION</literal> clause sets the compression method
+ for a column. Compression is supported only for variable-width data
+ types, and is used only for columns whose storage type is main or
+ extended. (See <xref linkend="sql-altertable"/> for information on
+ column storage types.) Setting this property for a partitioned table
+ has no direct effect, because such tables have no storage of their own,
+ but the configured value is inherited by newly-created partitions.
+ The supported compression methods are <literal>pglz</literal> and
+ <literal>lz4</literal>. <literal>lz4</literal> is available only if
+ <literal>--with-lz4</literal> was used when building
+ <productname>PostgreSQL</productname>. The default
is <literal>pglz</literal>.
</para>
</listitem>
diff --git a/src/backend/access/common/detoast.c b/src/backend/access/common/detoast.c
index b78d49167b..95d5b1c12a 100644
--- a/src/backend/access/common/detoast.c
+++ b/src/backend/access/common/detoast.c
@@ -477,8 +477,8 @@ toast_get_compression_oid(struct varlena *attr)
return InvalidOid;
/*
- * Just fetch the toast compress header to know the compression method
- * in the compressed data.
+ * Fetch just enough of the value to examine the compression header,
+ * so that we can find out the compression method.
*/
attr = toast_fetch_datum_slice(attr, 0, VARHDRSZ_COMPRESS);
}
@@ -503,7 +503,6 @@ toast_get_compression_handler(struct varlena *attr)
cmid = TOAST_COMPRESS_METHOD(attr);
- /* Get the handler routines for the compression method */
switch (cmid)
{
case PGLZ_COMPRESSION_ID:
diff --git a/src/backend/access/compression/compress_lz4.c b/src/backend/access/compression/compress_lz4.c
index 1856cf7df7..3079eff7eb 100644
--- a/src/backend/access/compression/compress_lz4.c
+++ b/src/backend/access/compression/compress_lz4.c
@@ -23,7 +23,7 @@
/*
* lz4_cmcompress - compression routine for lz4 compression method
*
- * Compresses source into dest using the default strategy. Returns the
+ * Compresses source into dest using the LZ4 defaults. Returns the
* compressed varlena, or NULL if compression fails.
*/
static struct varlena *
@@ -42,8 +42,8 @@ lz4_cmcompress(const struct varlena *value)
valsize = VARSIZE_ANY_EXHDR(value);
/*
- * Get maximum size of the compressed data that lz4 compression may output
- * and allocate the memory for holding the compressed data and the header.
+ * Figure out the maximum possible size of the LZ4 output, add the bytes
+ * that will be needed for varlena overhead, and allocate that amount.
*/
max_size = LZ4_compressBound(valsize);
tmp = (struct varlena *) palloc(max_size + VARHDRSZ_COMPRESS);
@@ -83,10 +83,10 @@ lz4_cmdecompress(const struct varlena *value)
int32 rawsize;
struct varlena *result;
- /* allocate memory for holding the uncompressed data */
+ /* allocate memory for the uncompressed data */
result = (struct varlena *) palloc(VARRAWSIZE_4B_C(value) + VARHDRSZ);
- /* decompress data using lz4 routine */
+ /* decompress the data */
rawsize = LZ4_decompress_safe((char *) value + VARHDRSZ_COMPRESS,
VARDATA(result),
VARSIZE(value) - VARHDRSZ_COMPRESS,
diff --git a/src/backend/executor/nodeModifyTable.c b/src/backend/executor/nodeModifyTable.c
index f77deee399..920d9dd0d5 100644
--- a/src/backend/executor/nodeModifyTable.c
+++ b/src/backend/executor/nodeModifyTable.c
@@ -2117,7 +2117,7 @@ CompareCompressionMethodAndDecompress(TupleTableSlot *slot,
TupleTableSlot *newslot = *outslot;
/*
- * If the called has passed an invalid slot then create a new slot.
+ * If the caller has passed an invalid slot then create a new slot.
* Otherwise, just clear the existing tuple from the slot. This slot
* should be stored by the caller so that it can be reused for
* decompressing the subsequent tuples.
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 18e8ecfd90..d8483c36b3 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1183,8 +1183,8 @@ typedef struct ModifyTableState
TupleTableSlot *mt_root_tuple_slot;
/*
- * Slot for storing the modified tuple, incase the target attribute's
- * compression method doesn't match with the source table.
+ * Slot for storing the modified tuple, in case the target attribute's
+ * compression method doesn't match that of the source table.
*/
TupleTableSlot *mt_decompress_tuple_slot;
--
2.17.0
--m51xatjYGsM+13rf
Content-Type: text/x-diff; charset=us-ascii
Content-Disposition: attachment;
filename="v24-0006-alter-table-set-compression.patch"
^ permalink raw reply [nested|flat] 2+ messages in thread
* Re: Let's make PostgreSQL multi-threaded
@ 2023-06-12 22:24 Michael Paquier <[email protected]>
0 siblings, 0 replies; 2+ messages in thread
From: Michael Paquier @ 2023-06-12 22:24 UTC (permalink / raw)
To: Andres Freund <[email protected]>; +Cc: Pavel Borisov <[email protected]>; Dilip Kumar <[email protected]>; Hannu Krosing <[email protected]>; Heikki Linnakangas <[email protected]>; pgsql-hackers
On Mon, Jun 12, 2023 at 12:24:30PM -0700, Andres Freund wrote:
> Those points seems pretty much unrelated to the potential gains from switching
> to a threading model. The main advantages are:
>
> 1) We'd gain from being able to share state more efficiently (using normal
> pointers) and more dynamically (not needing to pre-allocate). That'd remove
> a good amount of complexity. As an example, consider the work we need to do
> to ferry tuples from one process to another. Even if we just continue to
> use shm_mq, in a threading world we could just put a pointer in the queue,
> but have the tuple data be shared between the processes etc.
>
> Eventually this could include removing the 1:1 connection<->process/thread
> model. That's possible to do with processes as well, but considerably
> harder.
>
> 2) Making context switches cheaper / sharing more resources at the OS and
> hardware level.
Yes. FWIW, while reading the thread, parallel workers stroke me as
the first area that would benefit from all that. Could it be easier
to figure out the incremental pieces if working on a new node doing a
Gather based on threads, for instance?
--
Michael
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2021-02-10 21:56 [PATCH v24 05/10] fixups.patch Robert Haas <[email protected]>
2023-06-12 22:24 Re: Let's make PostgreSQL multi-threaded Michael Paquier <[email protected]>
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