This acts as a template of what can be achieved with the pluggable
cumulative stats APIs introduced in 7949d9594582 for the
variable-numbered case where stats entries are stored in the pgstats
dshash, while being potentially useful on its own for injection points,
say to add starting and/or stopping conditions based on the statistics
(want to trigger a callback after N calls, for example?).
Currently, the only data gathered is the number of times an injection
point is run. More fields can always be added as required. All the
routines related to the stats are located in their own file, called
injection_stats.c in the test module injection_points, for clarity.
The stats can be used only if the test module is loaded through
shared_preload_libraries. The key of the dshash uses InvalidOid for the
database, and an int4 hash of the injection point name as object ID.
A TAP test is added to provide coverage for the new custom cumulative
stats APIs, showing the persistency of the data across restarts, for
example.
Author: Michael Paquier
Reviewed-by: Dmitry Dolgov, Bertrand Drouvot
Discussion: https://postgr.es/m/Zmqm9j5EO0I4W8dx@paquier.xyz
<!-- doc/src/sgml/README.links -->
Linking within DocBook documents can be confusing, so here is a summary:
Intra-document Linking
----------------------
<xref>
use to get chapter/section number from the title of the target
link, or xreflabel if defined at the target, or refentrytitle if target
is a refentry; has no close tag
http://www.oasis-open.org/docbook/documentation/reference/html/xref.html
linkend=
controls the target of the link/xref, required
endterm=
for <xref>, allows the text of the link/xref to be taken from a
different link target title
<link>
use to supply text for the link, only uses linkend, requires </link>
http://www.oasis-open.org/docbook/documentation/reference/html/link.html
can be embedded inside of <command>, unlike <xref>
External Linking
----------------
<ulink>
like <link>, but uses a URL (not a document target); requires
</ulink>; if no text is specified, the URL appears as the link
text
http://www.oasis-open.org/docbook/documentation/reference/html/ulink.html
url=
used by <ulink> to specify the URL, required
Guidelines
----------
- For an internal link, if you want to supply text, use <link>, else
<xref>.
- Specific nouns like GUC variables, SQL commands, and contrib modules
usually have xreflabels.
- For an external link, use <ulink>, with or without link text.
- xreflabels added to tags prevent the chapter/section for id's from being
referenced; only the xreflabel is accessible. Therefore, use xreflabels
only when linking is common, and chapter/section information is unneeded.
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