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Disallow setting MAX_PARTITION_BUFFERS to less than 2

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Add some comments to mention that this value must be at least 2 and also
add a StaticAssertDecl to cause compilation failure if anyone tries to
build with an invalid value.

The multiInsertBuffers list must have at least two elements due to how the
code in CopyMultiInsertInfoFlush() pushes the current ResultRelInfo's
CopyMultiInsertBuffer to the end of the list.  If the first element is
also the last element, bad things will happen.

Author: Zhang Mingli <avamingli@gmail.com>
Discussion: https://postgr.es/m/CAApHDvpQ6t9ROcqbD-OgqR04Kfq4vQKw79Vo6r5j%2BciHwsSfkA%40mail.gmail.com
This commit is contained in:
David Rowley 2024-07-30 20:19:59 +12:00
parent 72fe6d24a3
commit c19615fe39
1 changed files with 11 additions and 1 deletions

12
src/backend/commands/copyfrom.c

@ -68,7 +68,10 @@
*/
#define MAX_BUFFERED_BYTES 65535
/* Trim the list of buffers back down to this number after flushing */
/*
* Trim the list of buffers back down to this number after flushing. This
* must be >= 2.
*/
#define MAX_PARTITION_BUFFERS 32
/* Stores multi-insert data related to a single relation in CopyFrom. */
@ -550,6 +553,13 @@ CopyMultiInsertInfoFlush(CopyMultiInsertInfo *miinfo, ResultRelInfo *curr_rri,
*/
if (buffer->resultRelInfo == curr_rri)
{
/*
* The code below would misbehave if we were trying to reduce the
* list to less than two items.
*/
StaticAssertDecl(MAX_PARTITION_BUFFERS >= 2,
"MAX_PARTITION_BUFFERS must be >= 2");
miinfo->multiInsertBuffers = list_delete_first(miinfo->multiInsertBuffers);
miinfo->multiInsertBuffers = lappend(miinfo->multiInsertBuffers, buffer);
buffer = (CopyMultiInsertBuffer *) linitial(miinfo->multiInsertBuffers);