The recommended value is 25% of your total machine RAM. You should try some lower and higher values because in some cases we achieve good performance with a setting over 25%. The configuration really depends on your machine and the working data set. If your working set of data can easily fit into your RAM, then you might want to increase the shared_buffer value to contain your entire database, so that the whole working set of data can reside in cache. That said, you obviously do not want to reserve all RAM for PostgreSQL.
How expensive is a join?
It depends! It depends what the join criteria is, what indexes are present, how big the tables are, whether the relations are cached, what hardware is being used, what configuration parameters are set, whether statistics are up-to-date, what other activity is happening on the system, to name a few things.
- But we can still try and get a feel for what a couple simple scenarios look like and see what happens when:
- The number of tables being joined increases
- The number of rows in those tables increases
Indexes are present / not present
It’s interesting that when indexes are being used it almost doesn’t matter how many rows are in the table, as we can see their times are all more or less together.
.. Even with a query that already joins 150 tables w/ 100k rows each, adding another table is only an additional 1.2 ms increase. Cool!
.. Based on the improvement we saw with indexes previously, it’s not too much of a surprise that we get great performance with our million row tables as well. But still, joining 50 tables with 1M rows each, in just 12ms. Wow!
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Mr. Trump is a uniquely dysfunctional chief executive. He contributed to this latest failure of governance with some characteristic misbehavior: erratic, contradictory commitments; confusing tweets; even blowing up a negotiating session by crudely insulting vast swaths of humanity.
As Mitch McConnell, the Senate majority leader, said last week, “As soon as we figure out what he is for, then I would be convinced that we were not just spinning our wheels.”
.. The problem Mr. Trump poses for the rest of the constitutional system is not that he is too strong and overbearing, but that he is too weak and fitful.
For Congress, such a problem might easily present an opportunity. A president unsure of what he wants could be a chance for the legislative branch to put itself in the driver’s seat.
That nothing of the sort has happened suggests that Mr. Trump is far from the whole story of contemporary Washington’s debilitation. His weakness has shed light on Congress’s weakness, and should force legislators to face some tough questions about the state of their own institution.
.. Conservatives are accustomed to blaming that on aggression by the other two branches — an overweening executive and administrative state and a hyperactive judiciary. There is surely truth to that indictment. But we should acknowledge, too, that the aggression of the other two branches has often been invited by the willful weakness of the Congress.
.. Not wishing to take responsibility for making hard choices, members of Congress (particularly when the president is of their party) have long been happy to enact vague legislation at best and to leave big decisions to the executive and judicial branches.
.. Is Congress’s purpose to
- implement the agenda of the majority party most effectively, or is its purpose to
- compel and enable accommodations in a divided country?
Today’s Congress does neither very well. But which failure is a bug and which is a feature?
.. Those two visions of Congress’s purpose (which the political scientist Daniel Stid labels “Wilsonian” and “Madisonian,” respectively) generally point in opposite directions when it comes to strengthening Congress,
.. The Wilsonian vision would have Congress function more like a European parliament, with stronger centralized leadership and fewer choke points and protections of minority prerogatives. It would enable the party that won a majority of seats to enact its agenda and see what voters make of it in the next election.
.. The Madisonian vision would recover the purpose of Congress in our larger constitutional system but would mean slow going, greater cacophony, less centralization and more opportunities for coalitions of strange bedfellows to form. It would have Congress serve as an arena for continuing bargaining and compromise, on the premise that greater social peace is better for the country than either party’s bright ideas.
A more parliamentary Congress has been the dream of progressive reformers for more than a century, but it is a poor fit not only for a system of divided powers but also for a polarized society. We need Congress to pursue and drive accommodations — in fact, as the political scientist Philip Wallach has recently argued, Congress is really the only institution in our system of government that could do that.
.. Too often, members in both parties seem to conceive of their work as performative rather than deliberative and use Congress as a platform to raise their profiles or build their personal brands before a larger audience, rather than letting Congress’s constitutional contours contain, reshape and channel their ambitions.
.. This is also how President Trump conceives of the presidency — and in some key respects how his predecessor did, too. It is how too many judges think of their work, and how too many journalists, professors and other professionals think of theirs. They think of institutions not as formative but as performative, not as molds that shape their character and actions but as platforms for displaying themselves and signaling their virtue.