Re: Fix memory leak in gist_page_items() of pageinspect

On Mon, Dec 15, 2025 at 4:12 PM Bertrand Drouvot <
bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:

> Hi,
>
> On Sat, Dec 13, 2025 at 10:37:40AM +0800, Chao Li wrote:
> > On Dec 12, 2025, at 18:29, Daniel Gustafsson <daniel(at)yesql(dot)se> wrote:
> >
> > On 12 Dec 2025, at 11:27, Heikki Linnakangas <hlinnaka(at)iki(dot)fi> wrote:
> >
> >
> > If we're going to bother changing this at all, let's consider reusing the
> > buffer. So instead of initStringInfo()+pfree on every tuple, allocate it
> > once and use resetStringInfo().
> >
> >
> > +1
> >
> > As Heikki suggested, I switched to using resetStringInfo() in 0002. One
> > thing I’d like to highlight is that this function only uses the
> StringInfo
> > buffer under certain conditions. If we initialize the StringInfo
> > unconditionally, that feels wasteful; if we initialize it lazily, as in
> > 0002, then we need some extra checks to manage its state.
>
> I think that 0002 works fine.
>
> I'm just wondering if:
>
> + StringInfoData buf = {0}; /* mark as uninitialized */
>
> does not "break" the semantic of "maxlen == 0" means "read-only".
>
> According to the StringInfoData definition comments:
>
> "
> * As a special case, a StringInfoData can be initialized with a read-only
> * string buffer. In this case "data" does not necessarily point at a
> * palloc'd chunk, and management of the buffer storage is the caller's
> * responsibility. maxlen is set to zero to indicate that this is the
> case.
> * Read-only StringInfoDatas cannot be appended to or reset.
> * Also, it is caller's option whether a read-only string buffer has a
> * terminating '\0' or not. This depends on the intended usage."
>
> The patch uses maxlen == 0 to detect "uninitialized", but the documentation
> explicitly says maxlen == 0 indicates "read-only". Maybe adjust the doc a
> bit or
> add a buf_initialized bool in gist_page_items instead?
>
>
Hi Bertrand,

I think your point is valid. Let's not break the current meaning of maxlen.
I added buf_initialized in v3. As 0001 has been pushed, v2-0002 now becomes
v3-0001.

Best regards,
Chao Li (Evan)
---------------------
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